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Practice › LeetCode › LeetCode 31xx ›

LeetCode 3158 - Find the XOR of Numbers Which Appear Twice

LeetCode Problem 3158 Difficulty: 🟢 Easy Topics: Array, Hash Table, Bit Manipulation Solution Problem Understanding This problem asks us to find all numbers in the array that appear exactly twice and compute the bitwise XOR of those numbers. The input is an integer array nums . The problem guarantees that every value appears either once or twice, never more than twice. Our task is not to count how many duplicate...

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LeetCode 3774 - Absolute Difference Between Maximum and Minimum K Elements

LeetCode Problem 3774 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem asks us to calculate the absolute difference between the sum of the k largest elements and the sum of the k smallest elements in a given array nums . In other words, we first need to identify the k smallest values, sum them up, then identify the k largest values, sum them, and finally compute the...

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LeetCode 3438 - Find Valid Pair of Adjacent Digits in String

LeetCode Problem 3438 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem gives us a string s containing only digits from '1' to '9' . We need to find the first adjacent pair of digits that satisfies two conditions. First, the two digits in the pair must be different. A pair like "22" or "55" is never valid. Second, each digit in the pair must appear...

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LeetCode 3633 - Earliest Finish Time for Land and Water Rides I

LeetCode Problem 3633 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Binary Search, Greedy, Sorting Solution Problem Understanding The problem asks us to determine the earliest possible time a tourist can finish exactly one land ride and one water ride at a theme park, where rides may be taken in either order. Each ride has a start time , representing when it becomes available, and a duration , representing how long...

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LeetCode 3637 - Trionic Array I

LeetCode Problem 3637 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding We are given an integer array nums and need to determine whether it can be divided into three consecutive segments that follow a very specific pattern: A strictly increasing segment. A strictly decreasing segment. A strictly increasing segment. More formally, we must find two indices p and q such that: 0 < p < q < n - 1...

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LeetCode 3602 - Hexadecimal and Hexatrigesimal Conversion

LeetCode Problem 3602 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The numbers that still fit in standard integer types; the algorithm scales logarithmically with digit count.

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LeetCode 3875 - Construct Uniform Parity Array I

LeetCode Problem 3875 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to determine if it is possible to construct a new array nums2 of the same length as nums1 where all elements are either all odd or all even. For each element nums2[i] , we can either copy the corresponding element from nums1[i] directly, or we can set it as the difference between nums1[i] and...

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LeetCode 3884 - First Matching Character From Both Ends

LeetCode Problem 3884 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution LeetCode 3884 - First Matching Character From Both Ends Problem Understanding This problem gives us a string s of length n consisting of lowercase English letters. For every index i , we compare two characters: The character at position i , which is s[i] The character at the mirrored position from the other end, which is s[n - i...

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LeetCode 3880 - Minimum Absolute Difference Between Two Values

LeetCode Problem 3880 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 3880 - Minimum Absolute Difference Between Two Values Problem Understanding The problem gives us an integer array nums where every element is guaranteed to be one of three values: 0 , 1 , or 2 . A pair of indices (i, j) is considered valid when: nums[i] == 1 nums[j] == 2 For every valid pair, we compute the...

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LeetCode 3870 - Count Commas in Range

LeetCode Problem 3870 Difficulty: 🟢 Easy Topics: Math Solution LeetCode 3870 - Count Commas in Range Problem Understanding The problem asks us to count how many commas appear when writing every integer from 1 through n using standard number formatting. In standard formatting, commas are inserted every three digits from the right side of the number. For example: 999 contains 0 commas. 1,000 contains 1 comma. 12,345 contains 1 comma....

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LeetCode 3866 - First Unique Even Element

LeetCode Problem 3866 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to find the first even integer in an array that appears exactly once . In other words, we need to traverse the array and identify even numbers, count their occurrences, and return the earliest one that occurs only a single time. If there is no such even number, we return -1 ....

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LeetCode 3769 - Sort Integers by Binary Reflection

LeetCode Problem 3769 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding This problem asks us to sort an array of positive integers based on a transformation called binary reflection . The binary reflection of a number is obtained by converting the number to its binary representation, reversing the order of the bits (ignoring leading zeros), and then interpreting the resulting binary string as a decimal integer. For example, the...

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LeetCode 3856 - Trim Trailing Vowels

LeetCode Problem 3856 Difficulty: 🟢 Easy Topics: String Solution LeetCode 3856 - Trim Trailing Vowels Problem Understanding This problem asks us to remove all vowels that appear at the end of a given string. The input is a string s consisting only of lowercase English letters. A vowel is defined as one of the five characters: 'a' , 'e' , 'i' , 'o' , or 'u' . The goal is...

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LeetCode 3852 - Smallest Pair With Different Frequencies

LeetCode Problem 3852 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution LeetCode 3852 - Smallest Pair With Different Frequencies Problem Understanding This problem gives us an integer array nums and asks us to find a pair of distinct values [x, y] that satisfies two conditions: x < y The frequency of x in the array is different from the frequency of y . Among all valid pairs, we must...

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LeetCode 3754 - Concatenate Non-Zero Digits and Multiply by Sum I

LeetCode Problem 3754 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to process an integer n and construct a new number using only its non-zero digits. These digits must remain in the same order in which they originally appear. After constructing this new integer x , we calculate the sum of its digits and then return the product: $$x \times \text{sum of digits of } x$$...

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LeetCode 3750 - Minimum Number of Flips to Reverse Binary String

LeetCode Problem 3750 Difficulty: 🟢 Easy Topics: Math, Two Pointers, String, Bit Manipulation Solution Problem Understanding The problem gives us a positive integer n , and asks us to work with its binary representation. First, we convert n into a binary string s without leading zeros. Then, we compute the reverse of that binary string. Our goal is to determine the minimum number of bit flips required so that s...

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LeetCode 3842 - Toggle Light Bulbs

LeetCode Problem 3842 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Simulation Solution LeetCode 3842 - Toggle Light Bulbs Problem Understanding The problem gives us an array bulbs , where each value represents a light bulb number between 1 and 100 . Initially, there are exactly 100 light bulbs, and every bulb is turned off. We process the array from left to right. For each value bulbs[i] : If that...

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LeetCode 3838 - Weighted Word Mapping

LeetCode Problem 3838 Difficulty: 🟢 Easy Topics: Array, String, Simulation Solution Problem Understanding The problem provides two inputs: words , an array of lowercase English strings. weights , an array of 26 integers where weights[i] represents the weight assigned to the letter corresponding to index i ( 0 -> 'a' , 1 -> 'b' , ..., 25 -> 'z' ). For every word, we must compute its total weight by...

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LeetCode 3833 - Count Dominant Indices

LeetCode Problem 3833 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 3833 - Count Dominant Indices Problem Understanding The problem gives us an integer array nums of length n . For every index i , we must determine whether the element nums[i] is dominant . An index is considered dominant if its value is strictly greater than the average of all elements to its right. In other words, for index...

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LeetCode 3803 - Count Residue Prefixes

LeetCode Problem 3803 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks us to analyze prefixes of a string s and count how many of them satisfy a specific condition. A prefix is any substring that starts at the first character and extends to some point in the string. For a prefix to be a residue , the number of distinct characters in that prefix must...

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LeetCode 3827 - Count Monobit Integers

LeetCode Problem 3827 Difficulty: 🟢 Easy Topics: Bit Manipulation, Enumeration Solution Problem Understanding The problem asks us to count Monobit integers from 0 to n . A Monobit integer is one where all bits in its binary representation are the same. This means there are only two possibilities for a valid Monobit integer: all zeros or all ones. For instance, 0 ( 0b0 ), 1 ( 0b1 ), 3 (...

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LeetCode 3736 - Minimum Moves to Equal Array Elements III

LeetCode Problem 3736 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to determine the minimum number of moves required to make every element in an integer array equal. A move consists of selecting one element and increasing it by exactly 1 . We are not allowed to decrease values, and we can only increment elements. In other words, we need to choose a target value...

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LeetCode 3823 - Reverse Letters Then Special Characters in a String

LeetCode Problem 3823 Difficulty: 🟢 Easy Topics: Two Pointers, String, Simulation Solution LeetCode 3823 - Reverse Letters Then Special Characters in a String Problem Understanding This problem gives us a string s that contains two types of characters: Lowercase English letters ( 'a' to 'z' ) Special characters from the set "!@#$%^&*()" We must perform two independent reversals, in a specific order. First, we extract all lowercase letters from the...

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LeetCode 3731 - Find Missing Elements

LeetCode Problem 3731 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding This problem asks us to reconstruct a missing sequence of integers from a partially incomplete array. We are given an integer array nums containing unique values , and we know an important fact: the array originally contained every integer in a continuous range , but some numbers were removed. Even though some values are missing, the...

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LeetCode 3813 - Vowel-Consonant Score

LeetCode Problem 3813 Difficulty: 🟢 Easy Topics: String, Simulation Solution LeetCode 3813 - Vowel-Consonant Score Problem Understanding The problem asks us to compute a score for a given string s . The string may contain lowercase English letters, spaces, and digits. We need to count two quantities: v , the number of vowels in the string. c , the number of consonants in the string. The vowels are exactly the...

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LeetCode 3712 - Sum of Elements With Frequency Divisible by K

LeetCode Problem 3712 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to compute the sum of all elements in the array whose total frequency is divisible by a given integer k . To understand the requirement clearly, we need to focus on two important details: First, we must determine how many times each number appears in the array. This is the element's frequency...

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LeetCode 3696 - Maximum Distance Between Unequal Words in Array I

LeetCode Problem 3696 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem gives us an array of strings, words , and asks us to find the maximum distance between two indices i and j where the words at those positions are different . More formally, we want to find two indices such that: words[i] != words[j] i < j the value j - i + 1 is as...

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LeetCode 3692 - Majority Frequency Characters

LeetCode Problem 3692 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks us to analyze the frequency distribution of characters in a string and identify a particular group of characters based on how often they appear. We are given a string s containing only lowercase English letters. For every distinct character, we first count how many times it appears. Characters with the same count belong...

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LeetCode 3794 - Reverse String Prefix

LeetCode Problem 3794 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution LeetCode 3794 - Reverse String Prefix Problem Understanding This problem gives us a string s and an integer k . Our task is to reverse only the first k characters of the string while leaving the remaining characters unchanged. In other words, we take the substring consisting of the first k characters, reverse its order, and then append the...

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LeetCode 3718 - Smallest Missing Multiple of K

LeetCode Problem 3718 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to find the smallest positive multiple of k that is not present in a given integer array nums . In other words, if we consider the infinite sequence of numbers k, 2k, 3k, 4k… , we need to identify the first number in this sequence that does not appear in nums . The...

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LeetCode 3550 - Smallest Index With Digit Sum Equal to Index

LeetCode Problem 3550 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem requires us to find the smallest index in an integer array nums such that the sum of the digits of the element at that index is equal to the index itself. In other words, for each index i , we calculate the sum of the digits of nums[i] and check if it equals i . If...

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LeetCode 3502 - Minimum Cost to Reach Every Position

LeetCode Problem 3502 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding We are given an array cost of length n . There are n + 1 positions in a line, numbered from 0 to n . Initially, we are standing at position n , which means we are at the very end of the line. To move forward in the line, we can swap positions with other people. The cost...

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LeetCode 3402 - Minimum Operations to Make Columns Strictly Increasing

LeetCode Problem 3402 Difficulty: 🟢 Easy Topics: Array, Greedy, Matrix Solution Problem Understanding The problem gives us a matrix grid of size m x n containing non-negative integers. Each column must become strictly increasing , meaning for each column j , the condition grid[i][j] < grid[i+1][j] must hold for all 0 <= i < m-1 . We are allowed to perform operations that increment any element by 1 , and...

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LeetCode 3745 - Maximize Expression of Three Elements

LeetCode Problem 3745 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting, Enumeration Solution LeetCode 3745 - Maximize Expression of Three Elements Problem Understanding The problem gives us an integer array nums and asks us to choose three elements a , b , and c from distinct indices such that the expression: $$a + b - c$$ is as large as possible. The important detail is that the three elements must come...

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LeetCode 3726 - Remove Zeros in Decimal Representation

LeetCode Problem 3726 Difficulty: 🟢 Easy Topics: Math, Simulation Solution LeetCode 3726 - Remove Zeros in Decimal Representation Problem Understanding The problem gives us a positive integer n and asks us to remove every digit '0' from its decimal representation. After all zero digits have been removed, we must return the resulting value as an integer. In other words, we first view the number as a sequence of decimal digits....

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LeetCode 3707 - Equal Score Substrings

LeetCode Problem 3707 Difficulty: 🟢 Easy Topics: String, Prefix Sum Solution Problem Understanding The problem asks us to determine if a given string s can be split into two non-empty substrings such that the sum of the alphabetic positions of characters in the left substring is equal to the sum in the right substring. Each character 'a' to 'z' maps to values 1 through 26 respectively. The input is a...

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LeetCode 3697 - Compute Decimal Representation

LeetCode Problem 3697 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding This problem asks us to decompose a positive integer n into the fewest possible base-10 components , where a base-10 component is defined as a single digit (1-9) multiplied by a power of 10. Essentially, we are breaking n down into its decimal place contributions . For example, for n = 537 , the hundreds place contributes 500,...

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LeetCode 3688 - Bitwise OR of Even Numbers in an Array

LeetCode Problem 3688 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation, Simulation Solution Problem Understanding This problem asks us to compute the bitwise OR of all even numbers in a given integer array nums . A number is considered even if it is divisible by 2, meaning its least significant bit is 0. The task is to iterate through the array, select only the even numbers, and combine them using the...

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LeetCode 3683 - Earliest Time to Finish One Task

LeetCode Problem 3683 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 3683 - Earliest Time to Finish One Task Problem Understanding The problem gives us a list of tasks, where each task is represented by two integers: si , the time when the task starts. ti , the amount of time required to complete the task. A task finishes at time: $$\text{finishTime} = s_i + t_i$$ Our goal is to determine...

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LeetCode 3684 - Maximize Sum of At Most K Distinct Elements

LeetCode Problem 3684 Difficulty: 🟢 Easy Topics: Array, Hash Table, Greedy, Sorting Solution Problem Understanding This problem requires selecting at most k distinct elements from a given array of positive integers nums such that their sum is maximized. The result must be returned as a list sorted in strictly descending order . The input nums represents a collection of numbers from which we can pick a subset. Each number can...

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LeetCode 3674 - Minimum Operations to Equalize Array

LeetCode Problem 3674 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation, Brainteaser Solution Let's go step by step and produce a fully detailed, reference-style solution guide for LeetCode 3674 following your requested formatting. Problem Understanding The problem asks us to make all elements of an integer array nums equal using the minimum number of operations. Each operation consists of selecting a contiguous subarray and replacing every element in that subarray with...

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LeetCode 3667 - Sort Array By Absolute Value

LeetCode Problem 3667 Difficulty: 🟢 Easy Topics: Array, Math, Two Pointers, Sorting Solution Problem Understanding The problem asks us to reorder an integer array such that the elements are sorted in non-decreasing order of their absolute values . This means we are not sorting based on the actual numeric value, but rather based on how far each number is from zero on the number line, regardless of sign. In simpler...

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LeetCode 3668 - Restore Finishing Order

LeetCode Problem 3668 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 3668 - Restore Finishing Order Problem Understanding This problem gives us two arrays: order , which represents the finishing order of all participants in a race. friends , which contains the IDs of our friends. The array order is a permutation of the integers from 1 to n , meaning every participant appears exactly once. The position of...

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LeetCode 3662 - Filter Characters by Frequency

LeetCode Problem 3662 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding This problem asks us to filter a string based on character frequency while preserving the original order of characters. We are given a string s consisting only of lowercase English letters and an integer k . The goal is to construct a new string by keeping only those characters whose total frequency in the entire string...

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LeetCode 3663 - Find The Least Frequent Digit

LeetCode Problem 3663 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Counting Solution Problem Understanding The problem asks us to find the least frequent digit in the decimal representation of a given integer n . In other words, we need to count how many times each digit from 0 to 9 appears in the number, and then return the smallest digit that occurs the fewest times. The input is a...

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LeetCode 3658 - GCD of Odd and Even Sums

LeetCode Problem 3658 Difficulty: 🟢 Easy Topics: Math, Number Theory Solution Problem Understanding The problem asks us to calculate the greatest common divisor (GCD) of two specific sums derived from an integer input n . The first sum, sumOdd , is the sum of the first n positive odd numbers, and the second sum, sumEven , is the sum of the first n positive even numbers. The input n is...

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LeetCode 3643 - Flip Square Submatrix Vertically

LeetCode Problem 3643 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Matrix Solution LeetCode 3643 - Flip Square Submatrix Vertically Problem Understanding This problem gives us an m x n matrix called grid and three integers: x , y , and k . The values x and y specify the top-left corner of a square submatrix, while k specifies the side length of that square. Therefore, the submatrix occupies: Problem Understanding...

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LeetCode 3622 - Check Divisibility by Digit Sum and Product

LeetCode Problem 3622 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine if a given positive integer n is divisible by the sum of two specific quantities derived from its digits: the digit sum and the digit product . The digit sum is obtained by adding all the digits of n , and the digit product is obtained by multiplying all the digits of n...

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LeetCode 3606 - Coupon Code Validator

LeetCode Problem 3606 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Sorting Solution Problem Understanding The problem is asking us to validate a set of coupons based on three criteria: the coupon code must be a non-empty string containing only alphanumeric characters or underscores, the business line must belong to a set of four predefined categories, and the coupon must be active. We are given three arrays of equal length,...

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LeetCode 3415 - Find Products with Three Consecutive Digits

LeetCode Problem 3415 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This is a SQL database problem involving pattern matching on strings. We are given a table named Products with two columns: Column Description product_id Unique identifier for each product name Product name string The goal is to return all products whose names contain a sequence of exactly three consecutive digits . The important detail is the word exactly ....

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LeetCode 3591 - Check if Any Element Has Prime Frequency

LeetCode Problem 3591 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Counting, Number Theory Solution Problem Understanding This problem asks us to determine whether any number in an array appears a prime number of times. In other words, for each unique number in the input array nums , we calculate its frequency-the number of occurrences-and check if that frequency is a prime number. If at least one element has a...

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LeetCode 3582 - Generate Tag for Video Caption

LeetCode Problem 3582 Difficulty: 🟢 Easy Topics: String, Simulation Solution Problem Understanding The problem asks us to transform a given caption string into a valid video tag following a strict sequence of rules. The input is a single string caption consisting only of English letters and spaces. These words must be transformed into a single hashtag-style identifier. The transformation has three ordered steps. First, we must merge all words into...

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LeetCode 3571 - Find the Shortest Superstring II

LeetCode Problem 3571 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to construct the shortest string that contains two given strings, s1 and s2 , as substrings. In other words, we are asked to merge s1 and s2 in such a way that no unnecessary characters are added, but both strings appear contiguously somewhere in the resulting string. The inputs, s1 and s2 , are both...

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LeetCode 3570 - Find Books with No Available Copies

LeetCode Problem 3570 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify books in a library system that are both fully unavailable for borrowing and currently have active borrowers who have not returned them yet. We are given two tables. The library_books table contains static information about each book, including how many total physical copies exist in the library. The borrowing_records table captures individual borrow...

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LeetCode 3560 - Find Minimum Log Transportation Cost

LeetCode Problem 3560 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to transport two logs of lengths n and m using three trucks, where each truck can carry a log of length at most k . If a log is longer than k , it must be cut into smaller pieces. Cutting a log of length x into two pieces of lengths len1 and len2 incurs...

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LeetCode 3545 - Minimum Deletions for At Most K Distinct Characters

LeetCode Problem 3545 Difficulty: 🟢 Easy Topics: Hash Table, String, Greedy, Sorting, Counting Solution LeetCode 3545 - Minimum Deletions for At Most K Distinct Characters Problem Understanding The problem gives us a string s containing lowercase English letters and an integer k . We are allowed to delete any characters from the string, including multiple occurrences of the same character. After performing the deletions, the resulting string must contain at...

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LeetCode 3541 - Find Most Frequent Vowel and Consonant

LeetCode Problem 3541 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem requires analyzing a string s composed of lowercase English letters and determining the sum of the maximum frequency of vowels and the maximum frequency of consonants. Vowels are defined as 'a' , 'e' , 'i' , 'o' , and 'u' . All other letters are consonants. The frequency of a character is the number...

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LeetCode 3536 - Maximum Product of Two Digits

LeetCode Problem 3536 Difficulty: 🟢 Easy Topics: Math, Sorting Solution LeetCode 3536 - Maximum Product of Two Digits Problem Understanding The problem gives us a positive integer n and asks us to find the maximum product that can be formed by multiplying any two digits that appear in the number. The input is a single integer. We must examine all of its digits and determine which pair of digits produces...

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LeetCode 3516 - Find Closest Person

LeetCode Problem 3516 Difficulty: 🟢 Easy Topics: Math Solution LeetCode 3516 - Find Closest Person Problem Understanding This problem gives us three integers, x , y , and z , representing the positions of three people on a one-dimensional number line. Person 1 starts at position x , Person 2 starts at position y , and Person 3 remains stationary at position z . Both Person 1 and Person 2...

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LeetCode 3512 - Minimum Operations to Make Array Sum Divisible by K

LeetCode Problem 3512 Difficulty: 🟢 Easy Topics: Array, Math Solution LeetCode 3512 - Minimum Operations to Make Array Sum Divisible by K Problem Understanding The problem gives us an integer array nums and an integer k . We are allowed to repeatedly perform one operation: choose any index i and decrease nums[i] by exactly 1 . Our goal is to determine the minimum number of such operations needed so that...

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LeetCode 3507 - Minimum Pair Removal to Sort Array I

LeetCode Problem 3507 Difficulty: 🟢 Easy Topics: Array, Hash Table, Linked List, Heap (Priority Queue), Simulation, Doubly-Linked List, Ordered Set Solution LeetCode 3507 - Minimum Pair Removal to Sort Array I Problem Understanding We are given an array nums . At any step, we are not free to choose any adjacent pair. Instead, the operation is completely determined by the current state of the array: Find the adjacent pair whose...

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LeetCode 3498 - Reverse Degree of a String

LeetCode Problem 3498 Difficulty: 🟢 Easy Topics: String, Simulation Solution LeetCode 3498 - Reverse Degree of a String Problem Understanding The problem asks us to compute a special value called the reverse degree of a string. Normally, letters are assigned positions in the alphabet as: 'a' = 1 'b' = 2 ... 'z' = 26 However, this problem uses the reversed alphabet order , where: 'a' = 26 'b' =...

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LeetCode 3492 - Maximum Containers on a Ship

LeetCode Problem 3492 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding This problem describes a cargo ship with an n × n deck. Since each cell on the deck can hold exactly one container, the deck has a total capacity of: $$n^2$$ physical container positions. Every container has the same weight, w . The ship also has a maximum total weight limit, maxWeight . Even if the deck has enough...

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LeetCode 3491 - Phone Number Prefix

LeetCode Problem 3491 Difficulty: 🟢 Easy Topics: Array, String, Trie, Sorting Solution Problem Understanding The problem is asking us to determine whether any phone number in a given list is a prefix of another phone number. In simpler terms, if you have a list of strings representing numbers, you need to check that no string starts with another string from the list. If all numbers are independent prefixes, the output...

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LeetCode 3477 - Fruits Into Baskets II

LeetCode Problem 3477 Difficulty: 🟢 Easy Topics: Array, Binary Search, Segment Tree, Simulation, Ordered Set Solution Problem Understanding This problem asks us to simulate the placement of fruits into baskets following very specific rules. We are given two arrays of equal length, fruits and baskets . Each element in fruits represents the quantity of a fruit type, and each element in baskets represents the capacity of a basket. We need...

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LeetCode 3471 - Find the Largest Almost Missing Integer

LeetCode Problem 3471 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 3471 - Find the Largest Almost Missing Integer Problem Understanding The problem gives us an integer array nums and an integer k . We consider every contiguous subarray of length k . An integer is called almost missing if it appears in exactly one of those size- k subarrays. Our goal is to find the largest integer that...

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LeetCode 3461 - Check If Digits Are Equal in String After Operations I

LeetCode Problem 3461 Difficulty: 🟢 Easy Topics: Math, String, Simulation, Combinatorics, Number Theory Solution Problem Understanding This problem asks us to repeatedly transform a string of digits by summing consecutive pairs modulo 10, until only two digits remain, and then check whether those two digits are equal. In other words, we start with a string s of length at least 3 and, at each step, generate a new string where...

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LeetCode 3467 - Transform Array by Parity

LeetCode Problem 3467 Difficulty: 🟢 Easy Topics: Array, Sorting, Counting Solution LeetCode 3467 - Transform Array by Parity Problem Understanding The problem gives us an integer array nums and asks us to transform it using three operations that must be performed in a specific order. First, every even number must be replaced with 0 . Second, every odd number must be replaced with 1 . After this transformation, the array...

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LeetCode 3465 - Find Products with Valid Serial Numbers

LeetCode Problem 3465 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to query a database table called products to identify rows where the description column contains a valid serial number. A valid serial number is defined as a substring that begins with "SN", followed by exactly four digits, a hyphen, and then exactly four more digits. For example, SN1234-5678 is valid, but SN123-4567 or SN12345-6789 are...

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LeetCode 3456 - Find Special Substring of Length K

LeetCode Problem 3456 Difficulty: 🟢 Easy Topics: String Solution LeetCode 3456 - Find Special Substring of Length K Problem Understanding The problem gives us a string s and an integer k . We need to determine whether there exists a substring of length exactly k that satisfies three conditions. First, every character inside the substring must be identical. In other words, the substring must consist of only one distinct character...

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LeetCode 3450 - Maximum Students on a Single Bench

LeetCode Problem 3450 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem provides a list of student-seat assignments, where each entry has the form [student_id, bench_id] . Each pair indicates that a particular student is sitting on a particular bench. The goal is to determine which bench has the largest number of unique students sitting on it and return that count. The important detail is that a...

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LeetCode 3452 - Sum of Good Numbers

LeetCode Problem 3452 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 3452 - Sum of Good Numbers Problem Understanding This problem gives us an integer array nums and an integer k . For every position i , we need to determine whether nums[i] is a good number. A number is considered good if it is strictly greater than the element located k positions to its left, nums[i - k] , when...

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LeetCode 3442 - Maximum Difference Between Even and Odd Frequency I

LeetCode Problem 3442 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding This problem requires analyzing the frequency of characters in a given string and computing a specific difference. You are given a string s consisting only of lowercase English letters. For each character in the string, you can count how many times it appears. Some characters will appear an odd number of times , and some will...

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LeetCode 3436 - Find Valid Emails

LeetCode Problem 3436 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires us to identify valid email addresses from a Users table in a database. Each row contains a user_id and an email string. The definition of a valid email is very specific: it must contain exactly one @ symbol , end with .com , have a local part (before the @ ) composed solely of alphanumeric characters...

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LeetCode 3427 - Sum of Variable Length Subarrays

LeetCode Problem 3427 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution Problem Understanding The problem provides an integer array nums of length n . For each index i , we are asked to consider a subarray that ends at i but starts at start = max(0, i - nums[i]) . This effectively means the subarray has a variable length depending on the value of nums[i] but never extends beyond the...

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LeetCode 3423 - Maximum Difference Between Adjacent Elements in a Circular Array

LeetCode Problem 3423 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 3423 - Maximum Difference Between Adjacent Elements in a Circular Array Problem Understanding This problem gives us an integer array nums and asks us to find the largest absolute difference between any two adjacent elements. The important detail is that the array is circular . In a normal array, element i is adjacent only to elements i - 1 and...

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LeetCode 3417 - Zigzag Grid Traversal With Skip

LeetCode Problem 3417 Difficulty: 🟢 Easy Topics: Array, Matrix, Simulation Solution LeetCode 3417 - Zigzag Grid Traversal With Skip Problem Understanding This problem asks us to traverse a two-dimensional grid in a zigzag order while visiting only every other cell in the traversal sequence. The zigzag traversal follows a very specific pattern: Start at the top-left corner (0, 0) . Traverse the first row from left to right. Move down...

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LeetCode 3411 - Maximum Subarray With Equal Products

LeetCode Problem 3411 Difficulty: 🟢 Easy Topics: Array, Math, Sliding Window, Enumeration, Number Theory Solution LeetCode 3411 - Maximum Subarray With Equal Products Problem Understanding We are given an array nums consisting of positive integers. For any array arr , define: prod(arr) as the product of all elements. gcd(arr) as the greatest common divisor of all elements. lcm(arr) as the least common multiple of all elements. A subarray is called...

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LeetCode 3407 - Substring Matching Pattern

LeetCode Problem 3407 Difficulty: 🟢 Easy Topics: String, String Matching Solution LeetCode 3407. Substring Matching Pattern Problem Understanding The problem gives us two strings: s , the source string. p , a pattern string containing exactly one '*' . The special character '*' can represent any sequence of characters, including an empty sequence. The goal is to determine whether there exists some substring of s that can match the pattern...

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LeetCode 3687 - Library Late Fee Calculator

LeetCode Problem 3687 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Below is,000. This value is well within the limits of standard integer types, and the algorithm still performs only a single pass through the array. ::: This version is formatted as a complete LeetCode editorial-style reference document and includes all requested sections.

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LeetCode 3375 - Minimum Operations to Make Array Values Equal to K

LeetCode Problem 3375 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 3375 - Minimum Operations to Make Array Values Equal to K Problem Understanding The problem gives us an integer array nums and a target value k . Our goal is to transform the entire array so that every element becomes exactly equal to k . However, we cannot arbitrarily change values. Each operation follows a very specific rule....

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LeetCode 3360 - Stone Removal Game

LeetCode Problem 3360 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding In this game, Alice and Bob take turns removing stones from a pile. The rules are very strict because the number of stones removed on each turn is predetermined. Alice always goes first and must remove exactly 10 stones on her first move. After that, each move removes exactly 1 fewer stone than the previous move. This means...

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LeetCode 3270 - Find the Key of the Numbers

LeetCode Problem 3270 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem gives us three positive integers, num1 , num2 , and num3 . We must construct a new number called the key using the digits of these three numbers. The important detail is that every number must first be treated as a four digit number. If a number has fewer than four digits, we pad it with leading...

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LeetCode 3206 - Alternating Groups I

LeetCode Problem 3206 Difficulty: 🟢 Easy Topics: Array, Sliding Window Solution Problem Understanding The problem gives us a circular array called colors , where each element represents the color of a tile: 0 means red 1 means blue Because the tiles form a circle, the first and last tiles are considered adjacent. We need to count how many groups of exactly 3 contiguous tiles form an alternating group. A group...

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LeetCode 3151 - Special Array I

LeetCode Problem 3151 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to determine whether a given integer array is "special". An array is considered special if every pair of adjacent elements has different parity. Parity refers to whether a number is even or odd. Two numbers have different parity if one is even and the other is odd. For example: 2 and 5 have different parity...

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LeetCode 3074 - Apple Redistribution into Boxes

LeetCode Problem 3074 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution Problem Understanding The problem asks us to redistribute a collection of apple packs into boxes while using the minimum number of boxes . Each pack apple[i] contains a certain number of apples, and each box capacity[j] can hold up to a certain number of apples. Apples from a single pack can be split across multiple boxes, so we are...

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LeetCode 1913 - Maximum Product Difference Between Two Pairs

LeetCode Problem 1913 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding This problem asks us to find the maximum product difference between two pairs of numbers from a given array. Specifically, given an array nums , we need to select four distinct indices w, x, y, z to form two pairs (nums[w], nums[x]) and (nums[y], nums[z]) . The goal is to maximize the expression (nums[w] * nums[x]) - (nums[y]...

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LeetCode 1880 - Check if Word Equals Summation of Two Words

LeetCode Problem 1880 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to determine if the sum of the numerical values of two words equals the numerical value of a third word. Each word consists of lowercase letters from 'a' to 'j' . Each letter has a letter value , which is its zero-based position in the alphabet ( 'a' -> 0 , 'b' -> 1 ,...

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LeetCode 1844 - Replace All Digits with Characters

LeetCode Problem 1844 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding In this problem, we are given a string s where characters at even indices are always lowercase English letters, and characters at odd indices are always digits. The goal is to replace every digit with a new character computed from the character immediately before it. The operation is called shift(c, x) , which means: Start from character c Move...

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LeetCode 3432 - Count Partitions with Even Sum Difference

LeetCode Problem 3432 Difficulty: 🟢 Easy Topics: Array, Math, Prefix Sum Solution Problem Understanding The problem gives us an integer array nums and asks us to count how many valid partition points produce an even difference between the sum of the left part and the sum of the right part. A partition is created by choosing an index i such that: The left subarray is nums[0:i+1] The right subarray is...

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LeetCode 2837 - Total Traveled Distance

LeetCode Problem 2837 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires calculating the total distance traveled by each user based on ride data stored in a relational database. We are given two tables: Users and Rides . The Users table contains user_id and name , where user_id is unique. The Rides table contains ride_id , user_id , and distance , where ride_id is unique. Each row in...

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LeetCode 3032 - Count Numbers With Unique Digits II

LeetCode Problem 3032 Difficulty: 🟢 Easy Topics: Hash Table, Math, Dynamic Programming Solution Problem Understanding The problem asks us to count how many integers in the inclusive range [a, b] contain only unique digits . A number has unique digits if no digit appears more than once within that number. For example, the number 123 has unique digits because 1 , 2 , and 3 each appear exactly once. However,...

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LeetCode 2535 - Difference Between Element Sum and Digit Sum of an Array

LeetCode Problem 2535 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem gives us an array of positive integers called nums . We need to compute two different values from this array. The first value is the element sum, which is simply the sum of every number in the array. For example, if the array is [1, 15, 6, 3] , then the element sum is: $$1 +...

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LeetCode 3090 - Maximum Length Substring With Two Occurrences

LeetCode Problem 3090 Difficulty: 🟢 Easy Topics: Hash Table, String, Sliding Window Solution Problem Understanding The problem is asking for the maximum length of a substring in a given string s such that no character occurs more than twice within that substring. In other words, for any valid substring, each character can appear at most two times. You need to return the length of the longest such substring. The input...

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LeetCode 2687 - Bikes Last Time Used

LeetCode Problem 2687 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires us to identify the last time each bike was used based on a table of rides. Each row of the table corresponds to a unique ride and contains the ride_id , bike_number , start_time , and end_time . Our task is to produce a result showing the latest end_time for each bike. Additionally, the results must...

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LeetCode 2057 - Smallest Index With Equal Value

LeetCode Problem 2057 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us a 0-indexed integer array nums . We must find the smallest index i such that: $$i \bmod 10 = nums[i]$$ The expression i mod 10 means the remainder when i is divided by 10 . We are asked to scan the array and determine whether any index satisfies this condition. If multiple indices satisfy it,...

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LeetCode 2148 - Count Elements With Strictly Smaller and Greater Elements

LeetCode Problem 2148 Difficulty: 🟢 Easy Topics: Array, Sorting, Counting Solution Problem Understanding The problem gives us an integer array nums and asks us to count how many elements satisfy a very specific condition. For an element nums[i] to be counted, there must exist: at least one element in the array that is strictly smaller than nums[i] at least one element in the array that is strictly greater than nums[i]...

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LeetCode 2887 - Fill Missing Data

LeetCode Problem 2887 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem provides a Pandas DataFrame named products with three columns: Column Type name object quantity int price int The task is to replace all missing values in the quantity column with 0 . In other words, some products may not have a recorded quantity, represented as None (or equivalently NaN in a Pandas DataFrame). Whenever this happens, we...

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LeetCode 3105 - Longest Strictly Increasing or Strictly Decreasing Subarray

LeetCode Problem 3105 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 3105, Longest Strictly Increasing or Strictly Decreasing Subarray Problem Understanding The problem gives us an integer array nums and asks us to find the length of the longest contiguous subarray that is either strictly increasing or strictly decreasing. A subarray must consist of consecutive elements from the original array. This is important because we cannot skip elements. For example, in...

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LeetCode 2796 - Repeat String

LeetCode Problem 2796 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to extend the behavior of strings so that every string supports a replicate(x) method. The method should return a new string where the original string is repeated exactly x times. For example, if the string is "hello" and x = 2 , the result should be "hellohello" . If the string is "code" and x...

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LeetCode 2595 - Number of Even and Odd Bits

LeetCode Problem 2595 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem asks us to analyze the binary representation of a positive integer n and count how many 1 bits appear at even indices and how many appear at odd indices. Bit positions are counted from right to left , starting at index 0 . This means the least significant bit, the rightmost bit, is at index 0...

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LeetCode 2329 - Product Sales Analysis V

LeetCode Problem 2329 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate how much money each user has spent across all of their purchases. We are given two database tables: The Sales table stores purchase records. Each row represents a transaction involving a specific product bought by a user, along with the quantity purchased. The Product table stores the price of each product. To compute...

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LeetCode 2729 - Check if The Number is Fascinating

LeetCode Problem 2729 Difficulty: 🟢 Easy Topics: Hash Table, Math Solution Problem Understanding The problem gives us a three digit integer n . We must determine whether n is a fascinating number. A number is considered fascinating when we concatenate three values together: n 2 * n 3 * n After concatenation, the resulting number must contain every digit from 1 through 9 exactly once. The digit 0 must not...

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LeetCode 3264 - Final Array State After K Multiplication Operations I

LeetCode Problem 3264 Difficulty: 🟢 Easy Topics: Array, Math, Heap (Priority Queue), Simulation Solution LeetCode 3264 - Final Array State After K Multiplication Operations I Problem Understanding This problem asks us to repeatedly modify an array according to a very specific rule. We are given: An integer array nums An integer k , representing how many operations to perform An integer multiplier For each of the k operations, we must...

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LeetCode 2341 - Maximum Number of Pairs in Array

LeetCode Problem 2341 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to take an array of integers, nums , and repeatedly form pairs of equal numbers until no more pairs can be formed. Each operation removes exactly two identical numbers from the array, and we continue doing this until it is no longer possible. The goal is to return a list of two...

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LeetCode 2475 - Number of Unequal Triplets in Array

LeetCode Problem 2475 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem gives us a 0-indexed integer array nums , and we must count how many triplets (i, j, k) satisfy two conditions. First, the indices must be strictly increasing: 0 <= i < j < k < nums.length Second, the values at those indices must all be different from each other: nums[i] != nums[j] nums[i]...

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LeetCode 2704 - To Be Or Not To Be

LeetCode Problem 2704 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a very small testing utility that mimics the behavior of assertion libraries used in real software development. We need to create a function named expect that accepts any value and returns an object containing two methods: toBe and notToBe . The toBe method checks whether the original value and the provided value are...

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LeetCode 2404 - Most Frequent Even Element

LeetCode Problem 2404 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to identify the most frequent even number in an integer array nums . If multiple even numbers share the highest frequency, we should return the smallest among them. If the array contains no even numbers, the function should return -1 . The input array nums can have up to 2000 elements, each...

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LeetCode 2283 - Check if Number Has Equal Digit Count and Digit Value

LeetCode Problem 2283 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding This problem asks us to verify a self-descriptive property of a string of digits. You are given a string num of length n , where each character is a digit between '0' and '9'. The requirement is that for every index i in the string, the digit i must appear exactly num[i] times in the entire...

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LeetCode 3248 - Snake in Matrix

LeetCode Problem 3248 Difficulty: 🟢 Easy Topics: Array, String, Simulation Solution Problem Understanding The problem describes a snake moving inside an n x n grid. Every cell in the grid is assigned a numeric position using the formula: $$\text{grid}[i][j] = (i \times n) + j$$ This means the grid is numbered row by row, starting from the top-left corner. For example, when n = 3 , the grid looks like...

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LeetCode 2884 - Modify Columns

LeetCode Problem 2884 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem provides a Pandas DataFrame named employees with two columns: Column Type name object salary int Each row represents one employee and their current salary. The task is to modify the salary column so that every salary value becomes twice its original amount. In other words, for every row in the DataFrame, we must replace: $salary = salary...

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LeetCode 3190 - Find Minimum Operations to Make All Elements Divisible by Three

LeetCode Problem 3190 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem gives us an integer array nums . In one operation, we are allowed to either increase or decrease any single element by exactly 1. Our goal is to make every number in the array divisible by 3, while using the smallest possible number of operations. In other words, for each number, we want to determine how...

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LeetCode 2890 - Reshape Data: Melt

LeetCode Problem 2890 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to reshape a dataset from a wide format to a long format , also known as “melting” in data analysis. In the input DataFrame, each row represents a product, and each column beyond the first represents quarterly sales ( quarter_1 to quarter_4 ). The goal is to transform this data so that each row contains...

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LeetCode 2210 - Count Hills and Valleys in an Array

LeetCode Problem 2210 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to identify hills and valleys in an integer array nums . A hill is a position where the closest non-equal neighbors on both sides are smaller than the current value, and a valley is where those neighbors are larger. Consecutive elements with the same value are considered part of the same hill or valley, so...

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LeetCode 2363 - Merge Similar Items

LeetCode Problem 2363 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Ordered Set Solution Problem Understanding The problem gives us two collections of items, items1 and items2 , where every item is represented as a pair: [value, weight] The value acts like a unique identifier for an item, while weight represents that item's associated weight. Within each individual array, values are guaranteed to be unique, meaning no value appears twice...

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LeetCode 2848 - Points That Intersect With Cars

LeetCode Problem 2848 Difficulty: 🟢 Easy Topics: Array, Hash Table, Prefix Sum Solution Problem Understanding The problem asks us to determine how many integer points on a number line are covered by at least one car. Each car is represented as a range [starti, endi] of integers, inclusive. For example, a car [3,6] covers the points 3, 4, 5, and 6. The input nums is a 2D array of these...

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LeetCode 2441 - Largest Positive Integer That Exists With Its Negative

LeetCode Problem 2441 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Sorting Solution Problem Understanding The problem asks us to find the largest positive integer k in a given array nums such that its negative counterpart -k also exists in the array. In other words, for each positive integer in the array, we need to check whether its negative exists. If multiple positive integers satisfy this property, we return...

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LeetCode 2399 - Check Distances Between Same Letters

LeetCode Problem 2399 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding This problem asks us to verify whether a string follows a very specific spacing rule between repeated characters. We are given a string s that contains only lowercase English letters. Every character that appears in the string appears exactly twice. We are also given an integer array distance of size 26 , where each index corresponds...

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LeetCode 2855 - Minimum Right Shifts to Sort the Array

LeetCode Problem 2855 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us a 0-indexed array nums of length n containing distinct positive integers. The goal is to determine the minimum number of right shifts required to sort the array in strictly increasing order. A right shift moves each element at index i to (i + 1) % n , effectively rotating the array one step to the...

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LeetCode 2578 - Split With Minimum Sum

LeetCode Problem 2578 Difficulty: 🟢 Easy Topics: Math, Greedy, Sorting Solution Problem Understanding The problem asks us to take a positive integer num and split its digits into two non-negative integers num1 and num2 such that the sum num1 + num2 is minimized. Importantly, the digits of num must be entirely used between num1 and num2 , but their order can be rearranged, and leading zeros are allowed in both...

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LeetCode 2480 - Form a Chemical Bond

LeetCode Problem 2480 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to identify all valid chemical bonds that can form between elements in a given table. The Elements table contains three columns: symbol , type , and electrons . The type column is an enumeration of 'Metal' , 'Nonmetal' , and 'Noble' . The electrons column indicates how many electrons a metal can give or a...

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LeetCode 3110 - Score of a String

LeetCode Problem 3110 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to compute the score of a string, where the score is defined as the sum of the absolute differences of ASCII values of consecutive characters in the string. In other words, for a string s of length n , the score is calculated as: $$\text{score}(s) = |s[0] - s[1]| + |s[1] - s[2]| + \dots...

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LeetCode 2220 - Minimum Bit Flips to Convert Number

LeetCode Problem 2220 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem asks us to determine the minimum number of bit flips required to transform an integer start into another integer goal . A bit flip is defined as changing a single bit in the binary representation of a number from 0 to 1 or from 1 to 0 . The input consists of two non-negative integers start...

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LeetCode 2553 - Separate the Digits in an Array

LeetCode Problem 2553 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding This problem asks us to take an array of positive integers, nums , and transform it into another array, answer , where each element of nums is broken down into its constituent digits in order. The key requirement is that the order of the digits must reflect the original numbers’ order in the array. For example, if a...

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LeetCode 2239 - Find Closest Number to Zero

LeetCode Problem 2239 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us an integer array nums , and we need to return the number whose value is closest to 0 . The phrase "closest to zero" means we compare numbers using their absolute values. For example: |-2| = 2 |5| = 5 Since 2 < 5 , the number -2 is closer to zero than 5 ....

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LeetCode 3065 - Minimum Operations to Exceed Threshold Value I

LeetCode Problem 3065 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to find the minimum number of operations needed to ensure that every element in an array is at least k . Each operation consists of removing the smallest element from the array. Essentially, we are incrementally deleting the smallest values until all remaining elements are greater than or equal to k . The input is...

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LeetCode 3216 - Lexicographically Smallest String After a Swap

LeetCode Problem 3216 Difficulty: 🟢 Easy Topics: String, Greedy Solution Problem Understanding The problem requires transforming a string of digits into its lexicographically smallest form by performing at most one swap between adjacent digits of the same parity . Here, parity refers to whether a digit is even or odd. Two digits can only be swapped if both are odd or both are even. The input is a string s...

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LeetCode 2269 - Find the K-Beauty of a Number

LeetCode Problem 2269 Difficulty: 🟢 Easy Topics: Math, String, Sliding Window Solution Problem Understanding The problem asks us to calculate the k-beauty of a given integer num . To do this, we treat num as a string and examine every possible contiguous substring of length k . For each substring, we interpret it as an integer and check whether it divides the original number num evenly. The final answer is...

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LeetCode 2695 - Array Wrapper

LeetCode Problem 2695 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a class ArrayWrapper that encapsulates an array of integers and supports two operations in a custom way. First, when two instances of ArrayWrapper are added together using the + operator, the result should be the sum of all elements in both arrays. This is a non-standard behavior because normally adding objects would not...

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LeetCode 3069 - Distribute Elements Into Two Arrays I

LeetCode Problem 3069 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem is asking us to simulate a process where we distribute elements from a 1-indexed array of distinct integers nums into two separate arrays, arr1 and arr2 , following a set of deterministic rules. Initially, the first element of nums goes to arr1 , the second goes to arr2 . Starting from the third element, the placement...

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LeetCode 3046 - Split the Array

LeetCode Problem 3046 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to determine if an even-length array can be split into two equal-sized subarrays, each containing only distinct elements . In other words, we must partition the array nums of length n into nums1 and nums2 of size n/2 such that there are no repeated numbers within either subarray. The function should return...

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LeetCode 2574 - Left and Right Sum Differences

LeetCode Problem 2574 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution Problem Understanding The problem asks us to compute the absolute difference between the sum of elements to the left and the sum of elements to the right for each element in a given array nums . In other words, for every index i , we want to know how different the sums on either side of that index are....

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LeetCode 3304 - Find the K-th Character in String Game I

LeetCode Problem 3304 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation, Recursion, Simulation Solution Problem Understanding The problem defines an infinite string-building process that starts with the string "a" . At every operation, we take the current string and create a transformed version where every character is replaced by the next character in the alphabet. Then we append this transformed string to the original string. For example: "a" becomes "ab" "ab"...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2696 - Minimum String Length After Removing Substrings

LeetCode Problem 2696 Difficulty: 🟢 Easy Topics: String, Stack, Simulation Solution Problem Understanding The problem asks us to determine the minimum possible length of a string after repeatedly removing the substrings "AB" or "CD" . We are given a string s consisting solely of uppercase English letters. Each operation allows us to remove any occurrence of "AB" or "CD" from the string, and after removal, the remaining parts of the...

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LeetCode 2072 - The Winner University

LeetCode Problem 2072 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us two database tables, NewYork and California . Each table contains the exam scores of students from a university. Every row represents a single student, identified by a unique student_id , along with their score . The competition rule is straightforward. A student is considered an excellent student if their score is greater than or equal...

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LeetCode 2591 - Distribute Money to Maximum Children

LeetCode Problem 2591 Difficulty: 🟢 Easy Topics: Math, Greedy Solution Problem Understanding

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2180 - Count Integers With Even Digit Sum

LeetCode Problem 2180 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem asks us to count all positive integers less than or equal to a given number num such that the sum of their digits is even. In other words, we are asked to evaluate each integer 1 through num , compute the sum of its digits, and check whether that sum is divisible by 2. If it...

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LeetCode 3162 - Find the Number of Good Pairs I

LeetCode Problem 3162 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem gives us two integer arrays, nums1 and nums2 , along with a positive integer k . We need to count how many index pairs (i, j) satisfy the following condition: nums1[i] is divisible by nums2[j] * k In mathematical terms, a pair is considered good if: nums1[i] % (nums2[j] * k) == 0 The task...

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LeetCode 1945 - Sum of Digits of String After Convert

LeetCode Problem 1945 Difficulty: 🟢 Easy Topics: String, Simulation Solution Problem Understanding This problem asks us to take a string of lowercase English letters and convert it into a numeric value, then repeatedly transform that number by summing its digits. The first step is a deterministic encoding: each character 'a' through 'z' is mapped to its 1-indexed alphabet position, so 'a' = 1 , 'b' = 2 , ..., 'z'...

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LeetCode 2669 - Count Artist Occurrences On Spotify Ranking List

LeetCode Problem 2669 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Spotify that contains information about songs appearing in a Spotify ranking list. Each row represents one ranked track and contains three columns: id , a unique identifier for the row track_name , the name of the song artist , the name of the artist who performed the track The task is to...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3386 - Button with Longest Push Time

LeetCode Problem 3386 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us a sequence of keyboard button press events. Each event is represented as: [index, time] Here: index is the identifier of the button that was pressed. time is the moment when the press happened. The events are already sorted by increasing time, which is extremely important because it means we can process the presses in chronological...

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LeetCode 2042 - Check if Numbers Are Ascending in a Sentence

LeetCode Problem 2042 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to analyze a sentence represented as a string s and determine whether all numbers embedded in the sentence are strictly increasing from left to right. A sentence here is defined as a sequence of tokens separated by single spaces , where each token is either a word of lowercase English letters or a positive integer...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2726 - Calculator with Method Chaining

LeetCode Problem 2726 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to design a class named Calculator that supports basic arithmetic operations while enabling method chaining . Method chaining means that after calling one method, we can immediately call another method on the same object. For example: new Calculator(10).add(5).subtract(7).getResult() works because each mathematical method returns the same Calculator instance after updating its internal state. The class...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2824 - Count Pairs Whose Sum is Less than Target

LeetCode Problem 2824 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Binary Search, Sorting Solution Problem Understanding This problem asks us to count the number of unique pairs of indices (i, j) in a given integer array nums such that the sum of the two numbers at those indices is strictly less than a given target . The array is 0-indexed, so valid pairs satisfy 0 <= i < j <...

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LeetCode 2833 - Furthest Point From Origin

LeetCode Problem 2833 Difficulty: 🟢 Easy Topics: String, Counting Solution Problem Understanding This problem asks us to determine the maximum possible distance from the origin after performing a sequence of moves on a number line. We start at position 0 , and we are given a string moves , where each character represents one movement instruction. Each move can shift the current position either left ( -1 ) or right...

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LeetCode 2891 - Method Chaining

LeetCode Problem 2891 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem provides a Pandas DataFrame named animals with four columns: Column Type name object species object age int weight int The task is to return a new DataFrame containing only the names of animals whose weight is strictly greater than 100 . In addition to filtering the rows, the result must also be sorted by the weight column...

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LeetCode 3354 - Make Array Elements Equal to Zero

LeetCode Problem 3354 Difficulty: 🟢 Easy Topics: Array, Simulation, Prefix Sum Solution Problem Understanding The problem gives us an integer array nums , where some elements may already be zero and others are positive integers. We must choose a starting index curr such that nums[curr] == 0 , and also choose an initial movement direction, either left or right. Once the process begins, we repeatedly follow a set of movement...

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LeetCode 2937 - Make Three Strings Equal

LeetCode Problem 2937 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to make three strings s1 , s2 , and s3 identical by repeatedly deleting their rightmost characters. Each deletion is counted as one operation. The key restriction is that we cannot completely delete a string , so at least one character must remain in each string. If it is impossible to make all three strings...

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LeetCode 3051 - Find Candidates for Data Scientist Position

LeetCode Problem 3051 Difficulty: 🟢 Easy Topics: Database Solution You included two different LeetCode problems with conflicting templates. The second problem appears to be the one you want covered: LeetCode 3051 - Find Candidates for Data Scientist Position (Database) However, the required sections still reference Python and Go solutions, test cases with assert , and algorithm walkthroughs, which do not apply to a SQL database problem. For a Database problem,...

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LeetCode 3005 - Count Elements With Maximum Frequency

LeetCode Problem 3005 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution LeetCode 3005 - Count Elements With Maximum Frequency Problem Understanding The problem gives us an integer array nums , where every value is positive. We need to determine which elements appear most frequently, then return the total number of occurrences contributed by all such elements. In other words, we first compute the frequency of every distinct number in...

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LeetCode 2942 - Find Words Containing Character

LeetCode Problem 2942 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to process an array of lowercase strings words and a single lowercase character x , and return all indices of the words that contain this character. In simpler terms, for each string in the array, we must check whether x appears anywhere in that string. If it does, we record the index of that...

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LeetCode 2917 - Find the K-or of an Array

LeetCode Problem 2917 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution LeetCode 2917 - Find the K-or of an Array Problem Understanding This problem introduces a generalized version of the bitwise OR operation called the K-or . In a normal bitwise OR, a bit in the result becomes 1 if at least one number has that bit set. The K-or operation changes this rule. Instead of requiring one occurrence, a...

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LeetCode 3364 - Minimum Positive Sum Subarray

LeetCode Problem 3364 Difficulty: 🟢 Easy Topics: Array, Sliding Window, Prefix Sum Solution Problem Understanding The problem asks us to find the smallest positive sum among all subarrays whose lengths fall within a given range [l, r] . A subarray is a contiguous section of the array. We are allowed to choose any non-empty contiguous segment as long as: Its length is between l and r , inclusive. Its sum...

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LeetCode 2665 - Counter II

LeetCode Problem 2665 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to implement a counter object that maintains a mutable integer value, initialized to a given number init . This counter object must provide three operations: increment , decrement , and reset . The increment method increases the current counter value by 1 and returns the updated value. The decrement method decreases the current counter value...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3280 - Convert Date to Binary

LeetCode Problem 3280 Difficulty: 🟢 Easy Topics: Math, String Solution LeetCode 3280, Convert Date to Binary Problem Understanding The problem gives us a date string in the format yyyy-mm-dd . The year always has four digits, while the month and day always have two digits because of zero padding. We need to convert each of the three components, year, month, and day, into their binary representations. The important detail is...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2490 - Circular Sentence

LeetCode Problem 2490 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to determine whether a given sentence is circular . A sentence is defined as a string of words separated by a single space, with no leading or trailing spaces. Words contain only uppercase and lowercase English letters. The key condition for circularity is that each word's last character must match the first character of the...

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LeetCode 3131 - Find the Integer Added to Array I

LeetCode Problem 3131 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 3131 - Find the Integer Added to Array I Problem Understanding The problem gives us two integer arrays, nums1 and nums2 , which have the same length. We are told that every element in nums1 was modified by adding the same integer x , and after this transformation the resulting array became equal to nums2 . The word "equal" here...

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LeetCode 2078 - Two Furthest Houses With Different Colors

LeetCode Problem 2078 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding The problem is asking us to find the maximum distance between two houses that have different colors . You are given a 0-indexed list colors where each element represents the color of a house. The distance between two houses at indices i and j is defined as abs(i - j) - the absolute difference of their indices. The...

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LeetCode 2803 - Factorial Generator

LeetCode Problem 2803 Difficulty: 🟢 Easy Topics: — Solution LeetCode 2803 - Factorial Generator Problem Understanding This problem asks us to implement a generator that produces the factorial sequence up to a given integer n . Recall that the factorial of a positive integer is defined as: $$n! = n \times (n-1) \times (n-2) \times \dots \times 2 \times 1$$ Additionally, by definition: $$0! = 1$$ The generator should not...

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LeetCode 3099 - Harshad Number

LeetCode Problem 3099 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine whether a given integer is a Harshad number. A Harshad number is an integer that is divisible by the sum of its digits. We are given a single integer x , and we must perform two operations: Compute the sum of all digits in x Check whether x is divisible by that digit...

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LeetCode 1893 - Check if All the Integers in a Range Are Covered

LeetCode Problem 1893 Difficulty: 🟢 Easy Topics: Array, Hash Table, Prefix Sum Solution Problem Understanding The problem asks us to determine whether every integer within a given inclusive range [left, right] is covered by at least one of the intervals specified in the ranges array. Each element of ranges is itself an array [starti, endi] representing an inclusive interval, meaning the integers starti and endi are part of the interval....

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LeetCode 2367 - Number of Arithmetic Triplets

LeetCode Problem 2367 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Enumeration Solution Problem Understanding The problem requires us to find the number of arithmetic triplets in a strictly increasing array of integers. An arithmetic triplet (i, j, k) satisfies the conditions i < j < k , nums[j] - nums[i] == diff , and nums[k] - nums[j] == diff . Essentially, we are looking for sequences of three...

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LeetCode 2469 - Convert the Temperature

LeetCode Problem 2469 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem gives us a single floating point value named celsius , representing a temperature measured in degrees Celsius. Our task is to convert this temperature into two other temperature scales, Kelvin and Fahrenheit, and return both converted values in an array. The conversion formulas are provided directly in the statement: Kelvin = Celsius + 273.15 Fahrenheit = Celsius...

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LeetCode 3353 - Minimum Total Operations

LeetCode Problem 3353 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem is asking us to determine the minimum number of operations required to make all elements of an array equal , given a very specific operation. The operation allows choosing a prefix of the array, selecting any integer k , and adding k to every element in that prefix. A prefix is defined as any subarray starting from...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2540 - Minimum Common Value

LeetCode Problem 2540 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Binary Search Solution Problem Understanding The problem gives us two integer arrays, nums1 and nums2 , and both arrays are already sorted in non-decreasing order. Our task is to find the smallest integer that appears in both arrays. If there is no value shared between the two arrays, we must return -1 . In other words, we need...

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LeetCode 2744 - Find Maximum Number of String Pairs

LeetCode Problem 2744 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Simulation Solution LeetCode 2744 - Find Maximum Number of String Pairs Problem Understanding This problem gives us an array words containing distinct strings. Every string has length exactly 2 , and all strings consist of lowercase English letters. We can form a pair between two strings words[i] and words[j] when: i < j One string is exactly the reverse...

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LeetCode 2733 - Neither Minimum nor Maximum

LeetCode Problem 2733 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem asks us to select a number from an array of distinct positive integers such that the chosen number is neither the minimum nor the maximum in the array. In other words, we must return a number that lies strictly between the smallest and largest elements. If all numbers are either the minimum or maximum (for example,...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2614 - Prime In Diagonal

LeetCode Problem 2614 Difficulty: 🟢 Easy Topics: Array, Math, Matrix, Number Theory Solution Problem Understanding The problem gives us a square matrix nums of size n x n . We need to examine the values that appear on the two diagonals of the matrix and return the largest value among them that is prime. There are two diagonals in a square matrix: The primary diagonal contains elements where the row...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3083 - Existence of a Substring in a String and Its Reverse

LeetCode Problem 3083 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem-Type Check This is a Type B, “Prove that” problem. The statement to prove is: Among all triangles determined by 100 points in general position, at most 70% are acute. The proposed proof attempts to establish a universal upper bound on the number of acute triangles. It does not need to characterize equality cases or extremal configurations. However, the...

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LeetCode 2609 - Find the Longest Balanced Substring of a Binary String

LeetCode Problem 2609 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a binary string s , which means the string contains only the characters '0' and '1' . We need to find the length of the longest substring that is considered balanced. A substring is balanced when two conditions are satisfied: All zeroes appear before all ones. The number of zeroes equals the number of ones....

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LeetCode 2682 - Find the Losers of the Circular Game

LeetCode Problem 2682 Difficulty: 🟢 Easy Topics: Array, Hash Table, Simulation Solution Problem Understanding This problem describes a circular passing game among n friends numbered from 1 to n . The ball always starts with friend 1 , and each turn increases the number of clockwise steps by a multiple of k . More specifically: On the first turn, the current player passes the ball 1 * k steps clockwise....

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LeetCode 2485 - Find the Pivot Integer

LeetCode Problem 2485 Difficulty: 🟢 Easy Topics: Math, Prefix Sum Solution LeetCode 2485 - Find the Pivot Integer Problem Understanding The problem gives us a positive integer n and asks us to find a special integer x , called the pivot integer, such that: The sum of all integers from 1 to x is equal to The sum of all integers from x to n The important detail is that...

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LeetCode 2843 - Count Symmetric Integers

LeetCode Problem 2843 Difficulty: 🟢 Easy Topics: Math, Enumeration Solution Problem Understanding The problem asks us to count symmetric integers within a given range [low, high] . A symmetric integer is defined as an integer with an even number of digits , where the sum of the first half of the digits is equal to the sum of the second half. For example, 1221 is symmetric because the sum of...

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LeetCode 2206 - Divide Array Into Equal Pairs

LeetCode Problem 2206 Difficulty: 🟢 Easy Topics: Array, Hash Table, Bit Manipulation, Counting Solution Problem Understanding The problem gives us an integer array nums containing exactly 2 * n elements. Our task is to determine whether it is possible to split the array into n valid pairs, where each pair contains two identical numbers. In simpler terms, every number in the array must be matched with another occurrence of the...

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LeetCode 3142 - Check if Grid Satisfies Conditions

LeetCode Problem 3142 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem gives us a two dimensional matrix called grid with m rows and n columns. We must verify whether every cell satisfies two separate rules. The first rule applies vertically. For every cell, if there is a cell directly below it, both values must be equal. In other words: grid[i][j] == grid[i + 1][j] The second rule...

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LeetCode 1941 - Check if All Characters Have Equal Number of Occurrences

LeetCode Problem 1941 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks us to determine whether a given string s is good , meaning that all characters that appear in the string occur the same number of times . In other words, if you count the frequency of each distinct character, those frequencies should be identical for the string to be considered good. The input...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1897 - Redistribute Characters to Make All Strings Equal

LeetCode Problem 1897 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks whether it is possible to make all strings in the input array words equal by redistributing characters between them. Specifically, in one operation, you can pick any character from one string and move it to another string at any position. The goal is to determine if, after potentially many such operations, every string...

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LeetCode 2335 - Minimum Amount of Time to Fill Cups

LeetCode Problem 2335 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting, Heap (Priority Queue) Solution Problem Understanding The problem gives us an array amount of length 3 . Each index represents the number of cups that need to be filled for a specific water type: amount[0] represents cold water cups amount[1] represents warm water cups amount[2] represents hot water cups Every second, the machine can perform exactly one of these operations:...

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LeetCode 2980 - Check if Bitwise OR Has Trailing Zeros

LeetCode Problem 2980 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem asks us to determine whether we can select two or more elements from a given array of positive integers such that their bitwise OR produces a number whose binary representation ends with at least one zero . In other words, the least significant bit of the OR result should be 0 . The input is...

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LeetCode 2903 - Find Indices With Index and Value Difference I

LeetCode Problem 2903 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding The problem asks us to find two indices i and j in the array such that two conditions are satisfied simultaneously : The indices must be far enough apart: $$|i - j| \geq indexDifference$$ The values at those indices must differ enough: $$|nums[i] - nums[j]| \geq valueDifference$$ We may return any valid pair if multiple answers exist....

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2496 - Maximum Value of a String in an Array

LeetCode Problem 2496 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding This problem asks us to compute the maximum value of strings in an array according to a specific definition of value. Each string can either be entirely numeric or alphanumeric. If a string consists only of digits, its value is the integer it represents. If it contains any letters, its value is the length of the string. We...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2639 - Find the Width of Columns of a Grid

LeetCode Problem 2639 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem gives us a two dimensional integer matrix called grid with m rows and n columns. Our task is to compute the width of every column independently. The width of a column is defined as the maximum string length among all integers appearing in that column. The length calculation follows standard integer string formatting rules: Positive numbers...

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LeetCode 2960 - Count Tested Devices After Test Operations

LeetCode Problem 2960 Difficulty: 🟢 Easy Topics: Array, Simulation, Counting Solution Problem Understanding This problem asks us to simulate a sequence of device tests based on battery percentages. We are given a 0-indexed integer array batteryPercentages , where each element represents the current battery level of a device. We process the devices from left to right, starting at index 0 and ending at index n - 1 . For each...

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LeetCode 2389 - Longest Subsequence With Limited Sum

LeetCode Problem 2389 Difficulty: 🟢 Easy Topics: Array, Binary Search, Greedy, Sorting, Prefix Sum Solution Problem Understanding This problem asks us to determine, for each query, the maximum number of elements we can select from an array nums such that their sum does not exceed a given value. We are not required to maintain consecutive elements, only the relative order for subsequences, but in this problem the relative order does...

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LeetCode 2600 - K Items With the Maximum Sum

LeetCode Problem 2600 Difficulty: 🟢 Easy Topics: Math, Greedy Solution Problem Understanding The problem asks us to determine the maximum possible sum when picking exactly k items from a bag containing items labeled 1 , 0 , or -1 . The bag's composition is given by three non-negative integers: numOnes for the number of 1 s, numZeros for the number of 0 s, and numNegOnes for the number of -1...

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LeetCode 2303 - Calculate Amount Paid in Taxes

LeetCode Problem 2303 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding This problem is asking us to simulate a progressive tax system. We are given a list of tax brackets where each bracket specifies an upper bound of income and a tax percentage. Our task is to compute the total tax owed for a given income, taking into account that each bracket only taxes the portion of income within...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1925 - Count Square Sum Triples

LeetCode Problem 1925 Difficulty: 🟢 Easy Topics: Math, Enumeration Solution Problem Understanding This problem asks us to count all ordered triples (a, b, c) such that: 1 <= a, b, c <= n a² + b² = c² This is the classic Pythagorean theorem relationship. Any triple satisfying this condition is called a square triple in the problem statement. The important detail is that the triples are ordered. This means...

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LeetCode 2529 - Maximum Count of Positive Integer and Negative Integer

LeetCode Problem 2529 Difficulty: 🟢 Easy Topics: Array, Binary Search, Counting Solution LeetCode 2529 - Maximum Count of Positive Integer and Negative Integer Problem Understanding The problem gives us a sorted integer array nums in non-decreasing order. Our task is to count how many numbers are positive and how many numbers are negative, then return the larger of the two counts. A positive integer is any value greater than 0...

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LeetCode 2164 - Sort Even and Odd Indices Independently

LeetCode Problem 2164 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem asks us to take an integer array nums and sort its elements based on their indices in two separate ways: the elements at even indices should be sorted in non-decreasing order, and the elements at odd indices should be sorted in non-increasing order. The array is 0-indexed , so index 0 is considered even, index 1...

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LeetCode 3136 - Valid Word

LeetCode Problem 3136 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to determine whether a given string qualifies as a "valid word" according to four specific rules. First, the word must contain at least 3 characters. Any string shorter than 3 is automatically invalid. Second, every character in the string must be either: A lowercase English letter An uppercase English letter A digit from 0 to...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2331 - Evaluate Boolean Binary Tree

LeetCode Problem 2331 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to evaluate a full binary tree where each node represents either a boolean value or a boolean operation. Leaf nodes have values 0 (False) or 1 (True). Non-leaf nodes have values 2 (OR) or 3 (AND). The goal is to compute the boolean value at the root by recursively evaluating all...

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LeetCode 3318 - Find X-Sum of All K-Long Subarrays I

LeetCode Problem 3318 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sliding Window, Heap (Priority Queue) Solution Problem Understanding The problem asks us to compute a special value called the x-sum for every contiguous subarray of length k . For each window of size k , we first count how many times each number appears. After that, we only keep the contributions of the top x most frequent distinct values. If...

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LeetCode 2990 - Loan Types

LeetCode Problem 2990 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires identifying users who have taken both a "Refinance" loan and a "Mortgage" loan. The input is a table Loans containing loan_id , user_id , and loan_type . Each row represents one loan taken by a user, and loan_id is unique. We are asked to return a list of distinct user_id values who satisfy the condition of...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2797 - Partial Function with Placeholders

LeetCode Problem 2797 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem is asking us to implement a function partial that takes a target function fn and a list of arguments args . Some of these arguments may be placeholders represented by the string "_" . When the returned function partialFn is called with additional arguments restArgs , each placeholder in args should be replaced with elements from restArgs...

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LeetCode 2822 - Inversion of Object

LeetCode Problem 2822 Difficulty: 🟢 Easy Topics: — Solution LeetCode 2822 - Inversion of Object Problem Understanding This problem asks us to invert the relationship between keys and values in a JSON object or array. The input can be either: A JSON object, where keys are strings and values are strings. A JSON array, where indices act as keys and elements are strings. The goal is to create a new...

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LeetCode 1935 - Maximum Number of Words You Can Type

LeetCode Problem 1935 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem is asking us to determine how many words in a given string can be fully typed on a malfunctioning keyboard. The keyboard has some broken letter keys that cannot be used. The input consists of a string text containing words separated by spaces, and a string brokenLetters containing the distinct letters that are broken. The...

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LeetCode 2357 - Make Array Zero by Subtracting Equal Amounts

LeetCode Problem 2357 Difficulty: 🟢 Easy Topics: Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Simulation Solution LeetCode 2357 - Make Array Zero by Subtracting Equal Amounts Problem Understanding This problem gives us an array nums containing non-negative integers. We want to transform the entire array into zeros using a specific operation. In a single operation, we must choose a positive integer x that is less than or equal to...

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LeetCode 1929 - Concatenation of Array

LeetCode Problem 1929 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding This problem asks us to take an input array nums of length n and produce a new array ans of length 2n where the first half of ans is identical to nums and the second half is also identical to nums . In other words, ans is formed by concatenating nums with itself. The input nums is a...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2119 - A Number After a Double Reversal

LeetCode Problem 2119 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine whether a number remains unchanged after performing two digit reversals. A digit reversal means reading the digits of a number from right to left. However, any leading zeros that appear after reversing are removed automatically because integers do not store leading zeros. For example: Reversing 526 gives 625 Reversing 1800 gives 81 ,...

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LeetCode 2432 - The Employee That Worked on the Longest Task

LeetCode Problem 2432 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to identify which employee worked the task with the longest duration given a sequence of tasks completed by employees. Each task is represented in logs[i] = [idi, leaveTimei] , where idi is the employee id and leaveTimei is the time the task was completed. The start time of each task is implicitly defined: the first...

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LeetCode 2886 - Change Data Type

LeetCode Problem 2886 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem provides a Pandas DataFrame named students with four columns: Column Type student_id int name object age int grade float The task is straightforward: the grade column is incorrectly stored as floating-point values, and we must convert it into integer values. In other words, the problem asks us to modify the DataFrame so that the grade column changes...

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LeetCode 2656 - Maximum Sum With Exactly K Elements

LeetCode Problem 2656 Difficulty: 🟢 Easy Topics: Array, Greedy Solution LeetCode 2656 - Maximum Sum With Exactly K Elements Problem Understanding The problem gives us an integer array nums and an integer k . We must perform exactly k operations. During each operation, we choose one element from the array, add its value to our score, remove it from the array, and then insert a new element equal to the...

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LeetCode 2889 - Reshape Data: Pivot

LeetCode Problem 2889 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem gives us a Pandas DataFrame named weather with three columns: city , the name of a city month , the name of a month temperature , the recorded temperature for that city during that month The task is to reshape the table using a pivot operation. Instead of storing each (city, month, temperature) combination as a separate...

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LeetCode 3014 - Minimum Number of Pushes to Type Word I

LeetCode Problem 3014 Difficulty: 🟢 Easy Topics: Math, String, Greedy Solution LeetCode 3014 - Minimum Number of Pushes to Type Word I Problem Understanding We are given a word consisting of distinct lowercase English letters. We are allowed to completely redesign the mapping of letters onto the telephone keypad keys 2 through 9 . There are 8 available keys ( 2 to 9 ). Each letter must be assigned to...

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LeetCode 2423 - Remove Letter To Equalize Frequency

LeetCode Problem 2423 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks us to determine if we can remove exactly one character from a string word such that all remaining characters in the string have the same frequency . The input string consists of lowercase English letters and has a length between 2 and 100. The output is a boolean indicating whether this transformation is...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2626 - Array Reduce Transformation

LeetCode Problem 2626 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem is asking us to simulate a "reduce" operation on an array of integers without using the built-in Array.reduce method. The input consists of three elements: an array nums , a function fn , and an initial value init . The fn function takes two arguments: the accumulator (the result computed so far) and the current element of...

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LeetCode 2689 - Extract Kth Character From The Rope Tree

LeetCode Problem 2689 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Edit LeetCode 2689 - Extract Kth Character From The Rope Tree Problem Understanding This problem asks us to retrieve the k-th character from a string represented by a special binary tree called a rope tree . Instead of storing one large string directly, the string is distributed across the tree structure. Each node in the tree belongs...

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LeetCode 2264 - Largest 3-Same-Digit Number in String

LeetCode Problem 2264 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem requires identifying the largest "good" integer from a given string of digits. A "good" integer is defined as a substring of length 3 where all digits are identical. The input string num represents a large integer but is provided as a string, which allows us to handle leading zeros and lengths up to 1000 without numeric overflow....

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LeetCode 2828 - Check if a String Is an Acronym of Words

LeetCode Problem 2828 Difficulty: 🟢 Easy Topics: Array, String Solution LeetCode 2828 - Check if a String Is an Acronym of Words Problem Understanding This problem asks us to determine whether a given string s is exactly the acronym formed from an array of words. An acronym is created by taking the first character from each word in the words array and concatenating those characters in the same order as...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2377 - Sort the Olympic Table

LeetCode Problem 2377 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to return the rows of the Olympic table in a very specific sorted order. Each row represents a country and the number of gold, silver, and bronze medals that country won in the Olympic games. The table contains four columns: country , the country name gold_medals , the number of gold medals silver_medals , the...

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LeetCode 2287 - Rearrange Characters to Make Target String

LeetCode Problem 2287 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem gives us two strings, s and target . We are allowed to take characters from s and rearrange them in any order to form copies of target . Each character in s can only be used once. The goal is to determine the maximum number of complete copies of target that can be constructed...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2739 - Total Distance Traveled

LeetCode Problem 2739 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding This problem asks us to compute the maximum total distance a truck can travel given fuel stored in two tanks: mainTank , the truck's primary fuel tank. additionalTank , a reserve tank that can transfer fuel into the main tank under specific conditions. The truck consumes fuel at a fixed mileage of 10 kilometers per liter . The...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2562 - Find the Array Concatenation Value

LeetCode Problem 2562 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Simulation Solution Problem Understanding The problem is asking us to compute a special sum over a given array nums by repeatedly concatenating the first and last elements of the array until it is empty. The concatenation operation is not addition; it involves treating numbers as strings, joining them together, and then converting them back to integers. For example, concatenating 15...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3263 - Convert Doubly Linked List to Array I

LeetCode Problem 3263 Difficulty: 🟢 Easy Topics: Array, Linked List, Doubly-Linked List Solution Problem Understanding The problem asks us to convert a doubly linked list into a standard integer array while preserving the order of elements. In a doubly linked list, each node contains a value ( val ) and two pointers: next (pointing to the next node) and prev (pointing to the previous node). The input is a reference...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1876 - Substrings of Size Three with Distinct Characters

LeetCode Problem 1876 Difficulty: 🟢 Easy Topics: Hash Table, String, Sliding Window, Counting Solution Problem Understanding The problem asks us to count how many substrings of length exactly three contain only distinct characters. A substring is a continuous portion of the string, so for every position in the string, we can examine the next three consecutive characters and determine whether all three are different. For example, in the string "xyzzaz"...

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LeetCode 2200 - Find All K-Distant Indices in an Array

LeetCode Problem 2200 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding The problem requires identifying all indices in an array nums that are "k-distant" from at least one occurrence of a given value key . In other words, for each index i , we need to determine whether there exists some index j such that nums[j] == key and the distance between i and j is at most...

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LeetCode 2427 - Number of Common Factors

LeetCode Problem 2427 Difficulty: 🟢 Easy Topics: Math, Enumeration, Number Theory Solution Problem Understanding The problem gives us two positive integers, a and b , and asks us to count how many integers divide both numbers evenly. A number x is considered a common factor if: a % x == 0 b % x == 0 This means x divides both integers without leaving a remainder. For example, if a...

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LeetCode 2255 - Count Prefixes of a Given String

LeetCode Problem 2255 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to determine how many strings in a given array words are prefixes of a target string s . A prefix of a string is defined as any substring that starts at the first character and continues for any length up to the length of the string itself. For example, "ab" is a prefix of...

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LeetCode 2413 - Smallest Even Multiple

LeetCode Problem 2413 Difficulty: 🟢 Easy Topics: Math, Number Theory Solution Problem Understanding The problem asks us to find the smallest positive integer that is a multiple of both 2 and a given positive integer n . In other words, we are looking for the least common multiple (LCM) of 2 and n . The input n is guaranteed to be between 1 and 150 , which is a very...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1853 - Convert Date Format

LeetCode Problem 1853 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Days with a single column called day . Each value in this column is a valid SQL DATE , and every value is unique. The task is to transform each date into a human readable string format: "day_name, month_name day, year" For example: 2022-04-12 should become: Tuesday, April 12, 2022 The output...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2379 - Minimum Recolors to Get K Consecutive Black Blocks

LeetCode Problem 2379 Difficulty: 🟢 Easy Topics: String, Sliding Window Solution Problem Understanding The problem gives us a string called blocks , where each character represents the color of a block. A character 'B' means the block is black, and a character 'W' means the block is white. We are also given an integer k . Our goal is to make sure there exists at least one group of exactly...

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LeetCode 2347 - Best Poker Hand

LeetCode Problem 2347 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem gives us exactly five playing cards. Each card is represented by two pieces of information: ranks[i] represents the numerical rank of the card, from 1 to 13 suits[i] represents the suit of the card, using characters from 'a' to 'd' We need to determine the strongest poker hand that can be formed from these...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2356 - Number of Unique Subjects Taught by Each Teacher

LeetCode Problem 2356 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires calculating the number of unique subjects each teacher teaches in a university, given a table that maps teachers to subjects and departments. Each row in the Teacher table represents a specific combination of a teacher, a subject, and a department. A teacher may teach the same subject in multiple departments, but for this problem, we only...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2728 - Count Houses in a Circular Street

LeetCode Problem 2728 Difficulty: 🟢 Easy Topics: Array, Interactive Solution Problem Understanding The problem asks us to determine the number of houses on a circular street where we can only interact with the street through the provided Street interface. Each house has a door that can either be open or closed. We are initially positioned in front of one house, but we do not know which one, and the street...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2894 - Divisible and Non-divisible Sums Difference

LeetCode Problem 2894 Difficulty: 🟢 Easy Topics: Math Solution LeetCode 2894 - Divisible and Non-divisible Sums Difference Problem Understanding This problem gives us two positive integers, n and m . We need to examine every integer in the inclusive range [1, n] and separate the numbers into two groups based on divisibility by m . The first group contains all numbers that are not divisible by m . The sum...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2455 - Average Value of Even Numbers That Are Divisible by Three

LeetCode Problem 2455 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to calculate the average of all integers in an array nums that satisfy two conditions simultaneously: they must be even and divisible by 3 . In other words, we only consider numbers that are multiples of 6, because a number divisible by both 2 and 3 is divisible by 6. The input is a...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2629 - Function Composition

LeetCode Problem 2629 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement function composition . We are given an array of functions and must return a new function that combines all of them into a single callable function. In mathematics and programming, function composition means taking the output of one function and feeding it into the next. The important detail here is that the functions...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3120 - Count the Number of Special Characters I

LeetCode Problem 3120 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks us to count the number of special characters in a given string word . A character is defined as special if it appears in both lowercase and uppercase forms within the same string. For example, if 'a' appears as both 'a' and 'A' anywhere in word , then 'a' counts as a special character....

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LeetCode 2451 - Odd String Difference

LeetCode Problem 2451 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution LeetCode 2451 - Odd String Difference Problem Understanding The problem gives us an array of strings where every string has the same length. For each string, we construct a difference array by subtracting the alphabet position of consecutive characters. For example, the string "adc" produces: 'd' - 'a' = 3 'c' - 'd' = -1 So its difference...

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LeetCode 2806 - Account Balance After Rounded Purchase

LeetCode Problem 2806 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem is asking us to simulate a simple bank account deduction after making a purchase. You start with an initial balance of 100 dollars. The purchase amount is given as an integer, purchaseAmount , representing the cost of an item in dollars. However, before deducting the amount, the bank rounds the purchaseAmount to the nearest multiple of 10....

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2383 - Minimum Hours of Training to Win a Competition

LeetCode Problem 2383 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding The problem gives us two starting values, initialEnergy and initialExperience , which represent the player's stats before entering a sequence of competitions. We are also given two arrays, energy and experience , where each index corresponds to an opponent. To defeat opponent i , the player must satisfy two strict conditions at the moment the fight begins: Current...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2908 - Minimum Sum of Mountain Triplets I

LeetCode Problem 2908 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to find the minimum possible sum of a "mountain triplet" within a given array of integers. A mountain triplet is defined as three indices (i, j, k) such that i < j < k , nums[i] < nums[j] , and nums[k] < nums[j] . Essentially, the middle element must be strictly larger than both its...

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LeetCode 2339 - All the Matches of the League

LeetCode Problem 2339 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The Teams table contains the names of all teams participating in a league. Each row represents exactly one team, and the team_name column is guaranteed to contain unique values. The problem asks us to generate every possible match in the league under the following rule: Every pair of teams plays twice. In one match, Team A is the home...

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LeetCode 2205 - The Number of Users That Are Eligible for Discount

LeetCode Problem 2205 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a table named Purchases , where each row represents a purchase made by a user. Every record contains three fields: user_id , identifying the customer time_stamp , indicating when the purchase happened amount , representing how much money was spent The pair (user_id, time_stamp) is unique, which means the same user cannot have two purchases...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2506 - Count Pairs Of Similar Strings

LeetCode Problem 2506 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Bit Manipulation, Counting Solution Problem Understanding The problem gives us an array of strings called words . We must count how many pairs of indices (i, j) satisfy two conditions: i < j words[i] and words[j] are similar Two strings are considered similar if they contain exactly the same set of distinct characters, regardless of order or frequency. For...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2082 - The Number of Rich Customers

LeetCode Problem 2082 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Store . Each row in the table represents a single bill issued to a customer. The table contains three columns: bill_id , which uniquely identifies a bill customer_id , which identifies the customer associated with the bill amount , which stores the bill amount We need to determine how many distinct...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2248 - Intersection of Multiple Arrays

LeetCode Problem 2248 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Counting Solution Problem Understanding The problem is asking us to find the intersection of multiple arrays. Specifically, given a 2D array nums , where each nums[i] is a non-empty array of distinct positive integers , we want to identify which integers appear in every array in nums . The result should be sorted in ascending order. In simpler terms,...

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LeetCode 2243 - Calculate Digit Sum of a String

LeetCode Problem 2243 Difficulty: 🟢 Easy Topics: String, Simulation Solution Problem Understanding This problem asks us to repeatedly transform a numeric string until its length becomes less than or equal to a given integer k . We are given two inputs: s , a string consisting only of digit characters ( '0' through '9' ) k , an integer that determines the size of groups used during each transformation round...

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LeetCode 2022 - Convert 1D Array Into 2D Array

LeetCode Problem 2022 Difficulty: 🟢 Easy Topics: Array, Matrix, Simulation Solution Problem Understanding The problem asks us to transform a one-dimensional array, original , into a two-dimensional array with m rows and n columns. The construction is sequential: the first n elements of original form the first row, the next n elements form the second row, and this continues until all rows are filled. If the total number of elements...

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LeetCode 1974 - Minimum Time to Type Word Using Special Typewriter

LeetCode Problem 1974 Difficulty: 🟢 Easy Topics: String, Greedy Solution Problem Understanding The problem describes a circular typewriter containing all lowercase English letters from 'a' to 'z' . A pointer moves around this circular arrangement, and initially the pointer starts at 'a' . To type a character, the pointer must currently point at that character. Every action costs exactly one second. There are only two possible actions: Move the pointer...

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LeetCode 2769 - Find the Maximum Achievable Number

LeetCode Problem 2769 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem gives us two integers, num and t . We are allowed to perform a specific operation at most t times. In one operation, we must simultaneously modify both numbers involved: Increase or decrease x by 1 At the same time, increase or decrease num by 1 The goal is to determine the maximum possible starting value of...

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LeetCode 2278 - Percentage of Letter in String

LeetCode Problem 2278 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to calculate the percentage of a given character, letter , in a string s , and return it as an integer rounded down to the nearest whole percent. Essentially, we need to determine how many times the character occurs, divide by the total number of characters, multiply by 100, and then round down. The input...

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LeetCode 2094 - Finding 3-Digit Even Numbers

LeetCode Problem 2094 Difficulty: 🟢 Easy Topics: Array, Hash Table, Recursion, Sorting, Enumeration Solution Problem Understanding The problem gives us an array named digits , where every element is a single decimal digit from 0 to 9 . We must use exactly three elements from this array to build valid three digit integers. The important detail is that each digit can only be used as many times as it appears...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2194 - Cells in a Range on an Excel Sheet

LeetCode Problem 2194 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem is asking us to generate all the Excel-style cell references within a rectangular range given in string format. Each cell is identified by a column letter and a row number, for example "A1" or "K2" . The input string is formatted as "<col1><row1>:<col2><row2>" , where <col1> and <col2> are uppercase letters indicating the starting and ending columns,...

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LeetCode 2878 - Get the Size of a DataFrame

LeetCode Problem 2878 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to determine the size of a DataFrame named players . Specifically, it requires computing two values: the number of rows and the number of columns. In a DataFrame, rows represent individual records-in this case, players-and columns represent attributes of those records, such as player_id , name , age , position , and so on. The...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2504 - Concatenate the Name and the Profession

LeetCode Problem 2504 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to transform data in a SQL table named Person . Each row represents a person, with three columns: person_id , name , and profession . The profession column is an ENUM containing one of six possible values: 'Doctor' , 'Singer' , 'Actor' , 'Player' , 'Engineer' , or 'Lawyer' . The task is to return...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1971 - Find if Path Exists in Graph

LeetCode Problem 1971 Difficulty: 🟢 Easy Topics: Depth-First Search, Breadth-First Search, Union-Find, Graph Theory Solution Problem Understanding The problem asks us to determine whether a path exists between two nodes in an undirected graph. The graph is defined by n vertices labeled from 0 to n - 1 and a list of edges, where each edge connects two distinct vertices. The key points are that the graph is bi-directional ,...

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LeetCode 2716 - Minimize String Length

LeetCode Problem 2716 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks us to minimize the length of a given string s by repeatedly performing two types of deletion operations. In the first operation, we can pick a character at some index and delete the closest identical character to its left if one exists. In the second operation, we can pick a character and delete the...

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LeetCode 2798 - Number of Employees Who Met the Target

LeetCode Problem 2798 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to determine how many employees in a company have worked at least a minimum number of hours, specified by target . We are given a 0-indexed array hours , where hours[i] represents the total hours worked by employee i . The task is to count all employees whose worked hours are greater than or equal...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2951 - Find the Peaks

LeetCode Problem 2951 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding The problem is asking us to identify all the peaks in a given array mountain . A peak is an element that is strictly greater than its immediate neighbors. Importantly, the first and last elements of the array cannot be peaks because they do not have two neighbors. The input is a zero-indexed array of integers mountain with...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1854 - Maximum Population Year

LeetCode Problem 1854 Difficulty: 🟢 Easy Topics: Array, Counting, Prefix Sum Solution Problem Understanding The problem asks us to determine the year with the highest population given a list of birth and death years. Each element in the input logs is a pair [birthi, deathi] representing the inclusive start of life at birthi and exclusive end at deathi . In other words, a person is considered alive from their birth...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2810 - Faulty Keyboard

LeetCode Problem 2810 Difficulty: 🟢 Easy Topics: String, Simulation Solution Problem Understanding In this problem, we are given a string s that represents characters typed on a faulty keyboard. Most characters behave normally and are appended to the current text on the screen. However, whenever the character 'i' is typed, the keyboard does not insert the character itself. Instead, it immediately reverses the entire string that has already been built....

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LeetCode 2089 - Find Target Indices After Sorting Array

LeetCode Problem 2089 Difficulty: 🟢 Easy Topics: Array, Binary Search, Sorting Solution LeetCode 2089, Find Target Indices After Sorting Array Problem Understanding The problem gives us an integer array nums and an integer target . We must sort the array in non-decreasing order and then return every index where the value equals target . A target index is simply an index i such that: $nums[i] = target$ The important detail...

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LeetCode 2724 - Sort By

LeetCode Problem 2724 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to sort an array using a custom sorting rule. Instead of sorting elements directly by their own value, we are given a function fn that transforms each element into a numeric value, and that numeric value determines the order. In other words, every element in arr is assigned a sort key by calling fn(element) ....

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LeetCode 2697 - Lexicographically Smallest Palindrome

LeetCode Problem 2697 Difficulty: 🟢 Easy Topics: Two Pointers, String, Greedy Solution LeetCode 2697, Lexicographically Smallest Palindrome Problem Understanding The problem gives us a string s consisting only of lowercase English letters. We are allowed to replace characters in the string with other lowercase letters. Our goal is to transform the string into a palindrome. A palindrome is a string that reads the same forward and backward. This means that...

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LeetCode 2053 - Kth Distinct String in an Array

LeetCode Problem 2053 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Counting Solution Problem Understanding The problem asks us to find the kth distinct string in an array of strings. A string is considered distinct if it appears exactly once in the entire array. The important detail is that the order matters. We are not sorting the strings or rearranging them in any way. Instead, we must consider distinct strings...

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LeetCode 2511 - Maximum Enemy Forts That Can Be Captured

LeetCode Problem 2511 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding In this problem, we are given an array called forts , where each position represents one of three possible states: 1 means the fort belongs to us. 0 means there is an enemy fort. -1 means the position is empty. We want to move our army from one of our forts to an empty position. However, the...

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LeetCode 2373 - Largest Local Values in a Matrix

LeetCode Problem 2373 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem gives us an n x n square matrix called grid , where each cell contains an integer value. Our task is to construct a new matrix called maxLocal , whose dimensions are (n - 2) x (n - 2) . For every valid position in the output matrix, we examine a contiguous 3 x 3 submatrix...

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LeetCode 2864 - Maximum Odd Binary Number

LeetCode Problem 2864 Difficulty: 🟢 Easy Topics: Math, String, Greedy Solution LeetCode 2864 - Maximum Odd Binary Number Problem Understanding The problem gives us a binary string s , containing only '0' and '1' characters. We are allowed to rearrange the bits in any order we want, but we must use exactly the same bits that appear in the original string. Our goal is to create the largest possible binary...

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LeetCode 2651 - Calculate Delayed Arrival Time

LeetCode Problem 2651 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to calculate the arrival time of a train given its scheduled arrivalTime and the amount of delayedTime . Both times are expressed in hours using the 24-hour clock format. The goal is to determine the new arrival time after accounting for the delay. For example, if a train was scheduled to arrive at 15:00 and...

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LeetCode 3150 - Invalid Tweets II

LeetCode Problem 3150 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Tweets with two columns: Column Description tweet_id Unique identifier for each tweet content The text content of the tweet We need to identify all tweets that are considered invalid. A tweet becomes invalid if at least one of the following conditions is true: The tweet content length is greater than 140...

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LeetCode 2418 - Sort the People

LeetCode Problem 2418 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Sorting Solution LeetCode 2418, Sort the People Problem Understanding This problem gives us two arrays of equal length: names[i] represents the name of a person heights[i] represents the height of that same person The two arrays are aligned by index, meaning the person at index i has both the name names[i] and the height heights[i] . The goal is...

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LeetCode 2900 - Longest Unequal Adjacent Groups Subsequence I

LeetCode Problem 2900 Difficulty: 🟢 Easy Topics: Array, String, Dynamic Programming, Greedy Solution LeetCode 2900 - Longest Unequal Adjacent Groups Subsequence I Problem Understanding We are given two arrays of the same length: words[i] is a string. groups[i] is either 0 or 1 . We want to select a subsequence of words . A subsequence preserves the original order of elements, but we may skip any number of elements. The...

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LeetCode 2668 - Find Latest Salaries

LeetCode Problem 2668 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 2668 - Find Latest Salaries Problem Understanding This problem gives us a database table named Salary that stores employee salary records. Each employee may appear multiple times because older salary records are still kept in the table. The key observation is that salaries are guaranteed to increase every year, which means the largest salary value for an employee must represent...

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LeetCode 2883 - Drop Missing Data

LeetCode Problem 2883 Difficulty: 🟢 Easy Topics: — Solution LeetCode 2883 - Drop Missing Data Problem Understanding This problem provides a pandas DataFrame named students with three columns: Column Type student_id int name object age int Some rows contain missing values in the name column. In pandas, these missing values are represented as None or other null-like values. The task is to return a DataFrame that contains only the rows...

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LeetCode 2774 - Array Upper Bound

LeetCode Problem 2774 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to enhance JavaScript arrays with a method called upperBound() . Given a sorted array of numbers and a target value, the method should return the last index where the target appears. If the target does not exist in the array, the method should return -1 . The key detail is that the array is sorted...

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LeetCode 2703 - Return Length of Arguments Passed

LeetCode Problem 2703 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks for a function that returns the number of arguments passed to it. Essentially, we need to measure the length of the input in a dynamic, variadic sense. The input is presented as a JSON array in the examples, representing all the arguments passed to the function. The expected output is an integer representing how many distinct...

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LeetCode 3258 - Count Substrings That Satisfy K-Constraint I

LeetCode Problem 3258 Difficulty: 🟢 Easy Topics: String, Sliding Window Solution LeetCode 3258 - Count Substrings That Satisfy K-Constraint I Problem Understanding The problem gives us a binary string s , meaning the string contains only the characters '0' and '1' , along with an integer k . A substring is considered valid if it satisfies the k-constraint . The constraint is unusual because it uses an OR condition rather...

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LeetCode 2000 - Reverse Prefix of Word

LeetCode Problem 2000 Difficulty: 🟢 Easy Topics: Two Pointers, String, Stack Solution Problem Understanding The problem gives us a string word and a character ch . We must locate the first occurrence of ch inside the string. Once we find it, we reverse the substring starting at index 0 and ending at that occurrence, inclusive. After reversing that prefix, the remainder of the string stays exactly the same. For example,...

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LeetCode 2006 - Count Number of Pairs With Absolute Difference K

LeetCode Problem 2006 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem gives us an integer array nums and an integer k . We need to count how many pairs of indices (i, j) satisfy two conditions: i < j |nums[i] - nums[j]| == k The notation |x| represents the absolute value of x , meaning the distance between two numbers regardless of direction. For example,...

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LeetCode 2956 - Find Common Elements Between Two Arrays

LeetCode Problem 2956 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding This problem asks us to compare two integer arrays and count how many elements from one array appear in the other. More specifically, we need to compute two values: answer1 is the number of indices i in nums1 such that nums1[i] appears at least once in nums2 . answer2 is the number of indices i in nums2...

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LeetCode 3349 - Adjacent Increasing Subarrays Detection I

LeetCode Problem 3349 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us an integer array nums and an integer k . We need to determine whether the array contains two adjacent subarrays, each of length k , such that both subarrays are strictly increasing. A subarray is strictly increasing if every element is larger than the one before it. For example, [2, 5, 7] is strictly increasing...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2129 - Capitalize the Title

LeetCode Problem 2129 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to transform the capitalization of every word in a given title string according to a specific rule based on word length. We are given a string called title , which contains one or more words separated by single spaces. Each word contains only English alphabet characters, and there are no leading or trailing spaces. Our...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1909 - Remove One Element to Make the Array Strictly Increasing

LeetCode Problem 1909 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us a 0-indexed integer array nums and asks whether it is possible to make the array strictly increasing after removing exactly one element. A strictly increasing array means that every element must be greater than the previous one. Formally, for every valid index i , the condition nums[i - 1] < nums[i] must hold. The important...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2946 - Matrix Similarity After Cyclic Shifts

LeetCode Problem 2946 Difficulty: 🟢 Easy Topics: Array, Math, Matrix, Simulation Solution Problem Understanding This problem asks us to determine whether a matrix remains identical to its original form after applying a specific cyclic shifting operation exactly k times. We are given an m x n integer matrix mat , where m is the number of rows and n is the number of columns. Each row is processed differently depending...

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LeetCode 1952 - Three Divisors

LeetCode Problem 1952 Difficulty: 🟢 Easy Topics: Math, Enumeration, Number Theory Solution Problem Understanding The problem asks us to determine whether a given integer n has exactly three positive divisors . In other words, we want to check if there are precisely three distinct integers d such that n % d == 0 and d > 0 . For example, the number 4 has divisors 1, 2, and 4, which...

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LeetCode 2351 - First Letter to Appear Twice

LeetCode Problem 2351 Difficulty: 🟢 Easy Topics: Hash Table, String, Bit Manipulation, Counting Solution Problem Understanding The problem gives us a string s containing only lowercase English letters. We need to return the first letter whose second occurrence appears earliest in the string. This detail is extremely important. The problem is not asking for the first character that repeats somewhere later. Instead, it asks which character reaches its second appearance...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2619 - Array Prototype Last

LeetCode Problem 2619 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to enhance all JavaScript arrays so that they have a convenient method, last() , which returns the last element of the array. If the array is empty, it should return -1 . The input array is assumed to be a valid JSON array, meaning it can contain any valid JSON data type including numbers, strings,...

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LeetCode 1978 - Employees Whose Manager Left the Company

LeetCode Problem 1978 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to find employees in a company who meet two specific conditions. First, their salary must be strictly less than $30,000. Second, their manager has left the company, meaning there is no corresponding row for the manager in the Employees table even though the manager_id field in the employee's record still references that manager. The...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3300 - Minimum Element After Replacement With Digit Sum

LeetCode Problem 3300 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to transform an array of integers nums by replacing each element with the sum of its digits . After this transformation, we need to determine the minimum element in the resulting array. The input array nums consists of 1 to 100 elements, and each element ranges from 1 to 10,000. The constraints ensure that...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2230 - The Users That Are Eligible for Discount

LeetCode Problem 2230 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify all users who qualify for a discount based on their purchase history stored in the Purchases table. Each row in the table contains three pieces of information: user_id , the identifier of the user time_stamp , the exact date and time when a purchase occurred amount , the amount paid during that purchase...

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LeetCode 2299 - Strong Password Checker II

LeetCode Problem 2299 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to determine whether a given password string satisfies a set of security requirements. We are given a single string, password , and we must return true if every condition is satisfied, otherwise return false . A password is considered strong only if all of the following are true: The length is at least 8 characters....

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1920 - Build Array from Permutation

LeetCode Problem 1920 Difficulty: 🟢 Easy Topics: Array, Simulation Solution LeetCode 1920, Build Array from Permutation Problem Understanding The problem gives us a zero-based permutation array called nums . A permutation means that every integer from 0 to n - 1 appears exactly once, where n is the length of the array. Since the array contains distinct values and covers the full range, every value in nums is also a...

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LeetCode 2215 - Find the Difference of Two Arrays

LeetCode Problem 2215 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 2215, Find the Difference of Two Arrays Problem Understanding This problem asks us to compare two integer arrays and identify the unique values that appear in one array but not the other. We are given two 0-indexed integer arrays, nums1 and nums2 . The goal is to return a list containing two separate lists: The first list should...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1939 - Users That Actively Request Confirmation Messages

LeetCode Problem 1939 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify users who requested confirmation messages at least twice within a 24 hour time window. We are given two database tables: The Signups table contains one row per user and records when the user signed up. The user_id column is unique. The Confirmations table contains confirmation message requests. Every row represents a confirmation request...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2634 - Filter Elements from Array

LeetCode Problem 2634 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to implement a function that filters an array based on a custom condition defined by another function fn . The input consists of an integer array arr and a filtering function fn that can accept either one argument, the array element itself, or two arguments, the element and its index. The goal is to return...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2144 - Minimum Cost of Buying Candies With Discount

LeetCode Problem 2144 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution Problem Understanding This problem asks us to minimize the total amount of money spent when buying candies under a special discount rule. For every two candies that are purchased, we may take one additional candy for free. However, the free candy must have a cost less than or equal to the cheaper of the two purchased candies. The input...

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LeetCode 2169 - Count Operations to Obtain Zero

LeetCode Problem 2169 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem asks us to count the number of operations required to reduce either of two non-negative integers num1 or num2 to zero. An operation is defined as subtracting the smaller number from the larger one (or subtracting either if they are equal). We continue performing operations until at least one of the numbers becomes zero. The input...

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LeetCode 2108 - Find First Palindromic String in the Array

LeetCode Problem 2108 Difficulty: 🟢 Easy Topics: Array, Two Pointers, String Solution Problem Understanding The problem asks us to examine an array of strings, words , and identify the first string that is a palindrome. A palindrome is a string that reads the same forward and backward. In other words, the first character matches the last, the second matches the second-to-last, and so on. If no string in the array...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2877 - Create a DataFrame from List

LeetCode Problem 2877 Difficulty: 🟢 Easy Topics: — Solution LeetCode 2877 - Create a DataFrame from List Problem Understanding This problem asks us to create a Pandas DataFrame from a given two dimensional list named student_data . Each element of student_data is itself a list containing exactly two values: A student ID The student's age For example: [ [1, 15], [2, 11], [3, 11], [4, 20] ] represents four students....

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LeetCode 2154 - Keep Multiplying Found Values by Two

LeetCode Problem 2154 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Simulation Solution LeetCode 2154 - Keep Multiplying Found Values by Two Problem Understanding This problem asks us to repeatedly search for a value inside an integer array and double that value whenever it is found. We begin with the integer original . If that number exists anywhere in the array nums , we multiply it by two and repeat...

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LeetCode 3226 - Number of Bit Changes to Make Two Integers Equal

LeetCode Problem 3226 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem gives us two positive integers, n and k . We are allowed to perform one specific operation on n : choose any bit that is currently 1 in the binary representation of n and change it to 0 . We are not allowed to: Change a 0 bit into 1 Change bits in k Rearrange bits...

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LeetCode 3172 - Second Day Verification

LeetCode Problem 3172 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires identifying users who verified their signup exactly on the second day after registering. We have two tables: emails and texts . The emails table contains the email_id , the user_id , and the signup_date . The texts table records actions taken by emails, including whether they were verified, along with the action_date . The task is...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2558 - Take Gifts From the Richest Pile

LeetCode Problem 2558 Difficulty: 🟢 Easy Topics: Array, Heap (Priority Queue), Simulation Solution Problem Understanding The problem presents a scenario where we have multiple piles of gifts, represented as an integer array gifts , with each element indicating the number of gifts in that pile. Every second, you must choose the pile with the most gifts and reduce its count to the floor of its square root. The operation is...

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LeetCode 2853 - Highest Salaries Difference

LeetCode Problem 2853 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Salaries with three columns: Column Meaning emp_name Employee name department Employee department salary Employee salary The combination of (emp_name, department) is unique, meaning there are no duplicate employee entries within the same department. The task is to compute the absolute difference between: The highest salary in the Engineering department The highest salary...

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LeetCode 2190 - Most Frequent Number Following Key In an Array

LeetCode Problem 2190 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to find the integer that appears most frequently immediately after a given key value in the array. More specifically, we are given an integer array nums and an integer key , which is guaranteed to exist in the array. We need to examine every occurrence of key in nums . Whenever we...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3345 - Smallest Divisible Digit Product I

LeetCode Problem 3345 Difficulty: 🟢 Easy Topics: Math, Enumeration Solution Problem Understanding The problem gives us two integers, n and t . We must find the smallest integer greater than or equal to n whose digit product is divisible by t . The digit product of a number is obtained by multiplying all of its digits together. For example: The digit product of 16 is 1 × 6 = 6...

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LeetCode 3033 - Modify the Matrix

LeetCode Problem 3033 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem is asking us to take a given m x n matrix, potentially containing -1 values, and produce a modified matrix in which each -1 is replaced by the maximum value in its respective column. The input matrix is guaranteed to have at least one non-negative integer in each column, which ensures that a maximum value can...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2635 - Apply Transform Over Each Element in Array

LeetCode Problem 2635 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a custom version of the array transformation operation, similar to JavaScript’s Array.map , but without using the built in Array.map method. We are given two inputs: An integer array arr A mapping function fn The goal is to return a new array where each element is the result of applying the function fn...

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LeetCode 2727 - Is Object Empty

LeetCode Problem 2727 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to determine if a given object or array is empty. In JavaScript terms, an object is empty if it has no key-value pairs, while an array is empty if it has no elements. The input is guaranteed to be valid JSON parsed into a JavaScript object or array, which could be represented in Python as...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2185 - Counting Words With a Given Prefix

LeetCode Problem 2185 Difficulty: 🟢 Easy Topics: Array, String, String Matching Solution Problem Understanding The problem gives us two inputs: An array of strings called words A string called pref We must count how many strings inside words start with the string pref . A prefix means the beginning portion of a string. For example: "at" is a prefix of "attention" "pay" is a prefix of "pay" "code" is not...

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LeetCode 2873 - Maximum Value of an Ordered Triplet I

LeetCode Problem 2873 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 2873 - Maximum Value of an Ordered Triplet I Problem Understanding You are given an integer array nums and must choose three indices (i, j, k) such that: i < j < k The triplet value is (nums[i] - nums[j]) * nums[k] Among all valid ordered triplets, we want the maximum possible value. If every possible triplet produces a negative...

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LeetCode 3379 - Transformed Array

LeetCode Problem 3379 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem asks us to transform a given integer array nums into a new array result following specific movement rules. Each element in nums determines how many steps to move in a circular manner, either to the right (if positive) or left (if negative). Zero values remain unchanged. The circular array property means that moving past the last...

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LeetCode 3194 - Minimum Average of Smallest and Largest Elements

LeetCode Problem 3194 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Sorting Solution LeetCode 3194 - Minimum Average of Smallest and Largest Elements Problem Understanding The problem gives us an even-length integer array nums . We repeatedly perform the following operation until the array becomes empty: Remove the smallest element. Remove the largest element. Compute their average. Store that average in another array called averages . After all pairs have been...

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LeetCode 2869 - Minimum Operations to Collect Elements

LeetCode Problem 2869 Difficulty: 🟢 Easy Topics: Array, Hash Table, Bit Manipulation Solution LeetCode 2869 - Minimum Operations to Collect Elements Problem Understanding This problem gives us an array nums and an integer k . We repeatedly perform an operation where we remove the last element of the array and add it to our collection. The goal is to determine the minimum number of such operations required so that our...

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LeetCode 2549 - Count Distinct Numbers on Board

LeetCode Problem 2549 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Simulation Solution Problem Understanding The problem starts with a single integer n written on a board. Every day, we examine every number currently on the board. For each number x , we look for all integers i such that: 1 <= i <= n x % i == 1 Whenever such an integer i exists, we add it to...

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LeetCode 3246 - Premier League Table Ranking

LeetCode Problem 3246 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 3246 - Premier League Table Ranking Problem Understanding This problem asks us to generate a league standings table from a database table named TeamStats . Each row in the table represents a football team and stores how many matches the team has played, won, drawn, and lost. The main task is to compute two derived values for every team: points...

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LeetCode 3198 - Find Cities in Each State

LeetCode Problem 3198 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named cities , where each row represents a relationship between a state and one of its cities. The (state, city) pair is guaranteed to be unique because it is the primary key, which means the same city will not appear twice for the same state. The task is to produce a result table...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2114 - Maximum Number of Words Found in Sentences

LeetCode Problem 2114 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding In this problem, we are given an array of strings called sentences . Each string represents a sentence composed of lowercase English words separated by exactly one space. The problem asks us to determine the maximum number of words that appear in any single sentence. A key detail is how words are separated. The problem guarantees that: There...

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LeetCode 3358 - Books with NULL Ratings

LeetCode Problem 3358 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named books . Each row in the table represents a single book and contains information such as the book's ID, title, author, publication year, and rating. The important detail is that the rating column can contain NULL values. In SQL, NULL represents the absence of a value, meaning the book has not been...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2880 - Select Data

LeetCode Problem 2880 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem provides a pandas DataFrame named students with three columns: Column Description student_id Unique identifier for a student name Student name age Student age The task is to return only the name and age columns for the student whose student_id is equal to 101 . In other words, we need to filter the table so that only rows...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2706 - Buy Two Chocolates

LeetCode Problem 2706 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution Problem Understanding The problem is asking us to purchase exactly two chocolates from a store given their individual prices, while ensuring that after buying them we do not end up in debt. The input consists of an array prices , where each element represents the cost of one chocolate, and an integer money , which is the total money...

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LeetCode 3168 - Minimum Number of Chairs in a Waiting Room

LeetCode Problem 3168 Difficulty: 🟢 Easy Topics: String, Simulation Solution LeetCode 3168, Minimum Number of Chairs in a Waiting Room Problem Understanding The problem gives us a string s that represents events happening in a waiting room over time. Each character corresponds to one second. If the character is 'E' , one person enters the room and occupies a chair. If the character is 'L' , one person leaves the...

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LeetCode 2885 - Rename Columns

LeetCode Problem 2885 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to rename the column names of a Pandas DataFrame according to a fixed mapping. We are given a DataFrame named students with four columns: id first last age The goal is to return a DataFrame where these columns have been renamed to more descriptive names: Original Column New Column id student_id first first_name last last_name...

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LeetCode 3000 - Maximum Area of Longest Diagonal Rectangle

LeetCode Problem 3000 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 3000 - Maximum Area of Longest Diagonal Rectangle Problem Understanding The input consists of a 2D array dimensions , where each element represents a rectangle. For a rectangle dimensions[i] , the value dimensions[i][0] is its length and dimensions[i][1] is its width. For every rectangle, we can compute the length of its diagonal using the Pythagorean theorem: $$\text{diagonal} = \sqrt{length^2 +...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2309 - Greatest English Letter in Upper and Lower Case

LeetCode Problem 2309 Difficulty: 🟢 Easy Topics: Hash Table, String, Enumeration Solution Problem Understanding The problem gives us a string s containing only uppercase and lowercase English letters. Our task is to find the greatest English letter that appears in both lowercase and uppercase forms somewhere in the string. The answer must be returned as an uppercase letter. To understand this clearly, consider what "greatest" means in this context. Letters...

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LeetCode 2932 - Maximum Strong Pair XOR I

LeetCode Problem 2932 Difficulty: 🟢 Easy Topics: Array, Hash Table, Bit Manipulation, Trie, Sliding Window Solution Problem Understanding The problem gives us an integer array nums , and we must choose two numbers x and y from the array such that they form a strong pair . A pair is considered strong if: $$|x - y| \leq \min(x, y)$$ Among all valid strong pairs, we must compute the maximum possible...

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LeetCode 1961 - Check If String Is a Prefix of Array

LeetCode Problem 1961 Difficulty: 🟢 Easy Topics: Array, Two Pointers, String Solution Problem Understanding The problem is asking us to determine whether a given string s can be formed by concatenating the first k elements of an array words , where k is some positive integer less than or equal to the length of words . In other words, s must match exactly the prefix of the array when all...

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LeetCode 2236 - Root Equals Sum of Children

LeetCode Problem 2236 Difficulty: 🟢 Easy Topics: Tree, Binary Tree Solution Problem Understanding This problem gives us a binary tree that always contains exactly three nodes. There is one root node, one left child, and one right child. We must determine whether the value stored in the root node is equal to the sum of the values stored in its two children. In other words, if: root.val is the value...

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LeetCode 3274 - Check if Two Chessboard Squares Have the Same Color

LeetCode Problem 3274 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem gives us two chessboard coordinates, such as "a1" or "h8" , and asks whether the two squares have the same color on a standard 8 x 8 chessboard. A chessboard alternates between black and white squares. If one square is black, all horizontally or vertically adjacent squares are white, and vice versa. This alternating pattern means...

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LeetCode 1933 - Check if String Is Decomposable Into Value-Equal Substrings

LeetCode Problem 1933 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to determine if a given string s , consisting solely of digits '0' through '9' , can be split into consecutive value-equal substrings such that exactly one substring has length 2 and all remaining substrings have length 3. A value-equal substring is a sequence of identical characters, like "111" or "22" . The input is...

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LeetCode 3392 - Count Subarrays of Length Three With a Condition

LeetCode Problem 3392 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us an integer array nums and asks us to count how many contiguous subarrays of length exactly 3 satisfy a specific mathematical condition. For every subarray of length 3 , we look at: the first element the second element the third element If: $$\text{first} + \text{third} = \frac{\text{second}}{2}$$ then that subarray contributes 1 to the answer....

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LeetCode 2879 - Display the First Three Rows

LeetCode Problem 2879 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem requires displaying the first three rows of a given DataFrame named employees . The DataFrame contains four columns: employee_id , name , department , and salary . The input represents a table of employee records, and the expected output is a subset of this table containing only the first three rows in their original order. The problem...

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LeetCode 2273 - Find Resultant Array After Removing Anagrams

LeetCode Problem 2273 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Sorting Solution Problem Understanding This problem asks us to repeatedly remove words from an array when two adjacent words are anagrams of each other . We are given a 0-indexed string array words , where every string contains only lowercase English letters. During each operation, we may choose an index i such that the word at words[i] is an...

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LeetCode 2710 - Remove Trailing Zeros From a String

LeetCode Problem 2710 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to remove all trailing zeros from a string representing a positive integer. The input num is a string consisting only of digits with no leading zeros, and the length of the string is between 1 and 1000. The output should be a string representation of the same integer but without any zeros at the end....

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LeetCode 2235 - Add Two Integers

LeetCode Problem 2235 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem is asking for the sum of two integers num1 and num2 . In simpler terms, you are given two numbers, and you need to calculate their total. The input integers can be negative, zero, or positive, and the output should be a single integer representing the sum. The constraints specify that both num1 and num2 are within...

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LeetCode 2758 - Next Day

LeetCode Problem 2758 Difficulty: 🟢 Easy Topics: — Solution LeetCode 2758 - Next Day Problem Understanding This problem asks us to extend JavaScript's built in Date object by adding a new method called nextDay() . Once implemented, any valid Date instance should be able to call this method and receive a string representing the next calendar day in the format YYYY-MM-DD . The input is a valid JavaScript Date object....

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LeetCode 2566 - Maximum Difference by Remapping a Digit

LeetCode Problem 2566 Difficulty: 🟢 Easy Topics: Math, Greedy Solution Problem Understanding The problem asks us to maximize the difference between two numbers that can be created from a given integer num through a specific remapping operation. We are allowed to choose exactly one digit d1 from 0 through 9 , and replace all occurrences of that digit in num with another digit d2 , which can also be any...

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LeetCode 2073 - Time Needed to Buy Tickets

LeetCode Problem 2073 Difficulty: 🟢 Easy Topics: Array, Queue, Simulation Solution Problem Understanding This problem describes a queue of n people, each wanting to buy a certain number of tickets. The input is an array tickets where tickets[i] represents how many tickets the i-th person wants. The process works like a real-life queue: each person buys one ticket at a time , taking exactly 1 second per ticket , and...

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LeetCode 3114 - Latest Time You Can Obtain After Replacing Characters

LeetCode Problem 3114 Difficulty: 🟢 Easy Topics: String, Enumeration Solution Problem Understanding The problem gives us a string representing a time in 12-hour format using the pattern "HH:MM" . Some characters may already be fixed digits, while others are replaced with "?" . Our task is to replace every "?" with a digit so that the resulting time is both valid and as large as possible chronologically. The valid hour...

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LeetCode 1886 - Determine Whether Matrix Can Be Obtained By Rotation

LeetCode Problem 1886 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem gives us two square binary matrices, mat and target , both of size n x n . Each cell contains either 0 or 1 . Our task is to determine whether mat can be transformed into target by rotating it clockwise in 90 degree increments. A rotation can be performed multiple times. Since rotating a square...

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LeetCode 3095 - Shortest Subarray With OR at Least K I

LeetCode Problem 3095 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation, Sliding Window Solution Problem Understanding The problem asks us to find the shortest subarray within a given array nums such that the bitwise OR of all elements in that subarray is at least k . A subarray is any contiguous sequence of elements in nums . The input array consists of non-negative integers , and the integer k is in...

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LeetCode 2621 - Sleep

LeetCode Problem 2621 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to implement an asynchronous function sleep that pauses execution for a given number of milliseconds, specified by the input millis . In other words, when sleep(millis) is called, the function should return a promise that resolves after approximately millis milliseconds have passed. The resolved value can be any value, as the problem does not enforce...

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LeetCode 3184 - Count Pairs That Form a Complete Day I

LeetCode Problem 3184 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem asks us to find all pairs of indices (i, j) in an array hours such that i < j and the sum of hours[i] + hours[j] is an exact multiple of 24, which is considered a "complete day." In simpler terms, we are trying to count all unique pairs of hours that add up...

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LeetCode 3222 - Find the Winning Player in Coin Game

LeetCode Problem 3222 Difficulty: 🟢 Easy Topics: Math, Simulation, Game Theory Solution Problem Understanding The game gives us two types of coins: x coins worth 75 y coins worth 10 Two players, Alice and Bob, take turns. Alice always moves first. On every turn, the current player must select coins whose total value is exactly 115 . If a player cannot make such a move, that player loses immediately. We...

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LeetCode 2996 - Smallest Missing Integer Greater Than Sequential Prefix Sum

LeetCode Problem 2996 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem asks us to find the smallest missing integer in the array that is greater than or equal to the sum of the longest sequential prefix . A sequential prefix means the beginning part of the array where every number increases by exactly 1 compared to the previous number. Formally, for a prefix nums[0..i] ,...

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LeetCode 2124 - Check if All A's Appears Before All B's

LeetCode Problem 2124 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string s that contains only two possible characters, 'a' and 'b' . We must determine whether every 'a' appears before every 'b' . Another way to think about the requirement is this: once we encounter a 'b' , we should never see another 'a' later in the string. If an 'a' appears after a...

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LeetCode 1967 - Number of Strings That Appear as Substrings in Word

LeetCode Problem 1967 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to determine how many strings in the array patterns appear as substrings within a given string word . A substring is defined as a contiguous sequence of characters, meaning the characters must appear in order and without gaps inside word . We are given two inputs. The first input, patterns , is a list...

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LeetCode 2965 - Find Missing and Repeated Values

LeetCode Problem 2965 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Matrix Solution LeetCode 2965 - Find Missing and Repeated Values Problem Understanding The problem gives us an n x n matrix called grid . Every value in the matrix should normally contain all integers from 1 to n² exactly once. However, there is one mistake in the matrix: One number appears twice. One number is completely missing. Our task...

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LeetCode 2605 - Form Smallest Number From Two Digit Arrays

LeetCode Problem 2605 Difficulty: 🟢 Easy Topics: Array, Hash Table, Enumeration Solution Problem Understanding The problem gives us two arrays, nums1 and nums2 , where each array contains unique digits from 1 to 9 . We need to construct the smallest possible number such that the number contains at least one digit from each array. The phrase "contains at least one digit from each array" is the key requirement. A...

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LeetCode 2138 - Divide a String Into Groups of Size k

LeetCode Problem 2138 Difficulty: 🟢 Easy Topics: String, Simulation Solution LeetCode 2138 - Divide a String Into Groups of Size k Problem Understanding The problem asks us to split a string into consecutive groups, where every group must contain exactly k characters. We process the string from left to right. The first k characters form the first group, the next k characters form the second group, and so on. Every...

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LeetCode 2987 - Find Expensive Cities

LeetCode Problem 2987 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 2987 - Find Expensive Cities Problem Understanding This problem provides a database table named Listings that contains information about home listings. Each row represents a single home listing and contains three fields: listing_id , a unique identifier for the listing city , the city where the home is located price , the listed price of the home The task is...

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LeetCode 2325 - Decode the Message

LeetCode Problem 2325 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding This problem is asking us to decode a secret message using a substitution cipher defined by a key string. The key string may include spaces and contains every lowercase letter of the English alphabet at least once. The order in which each letter first appears in the key determines the mapping to the regular alphabet. For example,...

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LeetCode 3174 - Clear Digits

LeetCode Problem 3174 Difficulty: 🟢 Easy Topics: String, Stack, Simulation Solution Problem Understanding In this problem, we are given a string s that contains lowercase English letters and digits. The task is to repeatedly remove digits according to a very specific rule. Whenever we encounter a digit, we must delete two characters: The digit itself The closest non-digit character to its left This process continues until all digits are removed....

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LeetCode 2788 - Split Strings by Separator

LeetCode Problem 2788 Difficulty: 🟢 Easy Topics: Array, String Solution LeetCode 2788 - Split Strings by Separator Problem Understanding This problem asks us to process an array of strings and split each string using a given separator character. After performing all splits, we must collect every resulting substring into a single output array while preserving the original order. More specifically, we are given: words , an array of strings. separator...

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LeetCode 2500 - Delete Greatest Value in Each Row

LeetCode Problem 2500 Difficulty: 🟢 Easy Topics: Array, Sorting, Heap (Priority Queue), Matrix, Simulation Solution Problem Understanding The problem presents an m x n matrix grid of positive integers and asks us to simulate a repeated deletion process on it. In each operation, for every row in the matrix, we remove the greatest element. After deleting these elements, we take the largest of the removed elements from all rows and...

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LeetCode 3146 - Permutation Difference between Two Strings

LeetCode Problem 3146 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks us to compute the permutation difference between two strings, s and t . Both strings contain unique characters, and t is a permutation of s . The permutation difference is calculated by taking each character in s , finding its index in both s and t , and summing the absolute differences of these...

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LeetCode 2570 - Merge Two 2D Arrays by Summing Values

LeetCode Problem 2570 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers Solution Problem Understanding The problem gives us two sorted 2D integer arrays, nums1 and nums2 , where every element is a pair of integers in the form [id, value] . Each id uniquely identifies an entry inside its own array, and the corresponding value represents that id's associated number. Since both arrays are already sorted in ascending order...

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LeetCode 2176 - Count Equal and Divisible Pairs in an Array

LeetCode Problem 2176 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 2176, Count Equal and Divisible Pairs in an Array Problem Understanding The problem gives us a 0-indexed integer array nums and an integer k . We need to count how many pairs of indices (i, j) satisfy all of the following conditions: 0 <= i < j < n nums[i] == nums[j] (i * j) % k == 0 In...

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LeetCode 2899 - Last Visited Integers

LeetCode Problem 2899 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem gives us an integer array nums that contains either positive integers or the value -1 . We process the array from left to right while maintaining two conceptual arrays: seen , which stores previously encountered positive integers ans , which stores the answers for each -1 Whenever we encounter a positive integer, we insert it at...

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LeetCode 2928 - Distribute Candies Among Children I

LeetCode Problem 2928 Difficulty: 🟢 Easy Topics: Math, Combinatorics, Enumeration Solution Problem Understanding The problem asks us to calculate the number of ways to distribute n candies among exactly three children such that no child receives more than a specified limit of candies. In other words, we are looking for all integer triplets (a, b, c) such that a + b + c = n and each of a ,...

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LeetCode 3242 - Design Neighbor Sum Service

LeetCode Problem 3242 Difficulty: 🟢 Easy Topics: Array, Hash Table, Design, Matrix, Simulation Solution Problem Understanding The problem asks us to design a service that works on a square matrix, where every value in the matrix is unique. For any given value, we must efficiently compute two different types of neighbor sums. The first operation, adjacentSum(value) , returns the sum of all directly adjacent cells. These are the four cardinal...

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LeetCode 3063 - Linked List Frequency

LeetCode Problem 3063 Difficulty: 🟢 Easy Topics: Hash Table, Linked List, Counting Solution Problem Understanding This problem asks us to analyze a singly-linked list of integers and produce a new linked list containing the frequencies of each distinct element in the input list. Specifically, given the head of a linked list containing k distinct elements, we are to return another linked list of length k where each node represents the...

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LeetCode 2970 - Count the Number of Incremovable Subarrays I

LeetCode Problem 2970 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Binary Search, Enumeration Solution Problem Understanding The problem asks us to count all subarrays of a given array nums such that if we remove the subarray , the remaining array becomes strictly increasing. A strictly increasing array is one where each element is less than the next element. For example, [1,2,3] is strictly increasing, while [1,2,2] or [3,2,1] are not....

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LeetCode 3173 - Bitwise OR of Adjacent Elements

LeetCode Problem 3173 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem gives us an integer array nums of length n . We must create and return a new array called answer of length n - 1 . For every index i , the value at answer[i] should be the result of applying the bitwise OR operation between two adjacent elements in the original array: $answer[i] =...

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LeetCode 2515 - Shortest Distance to Target String in a Circular Array

LeetCode Problem 2515 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to find the shortest distance from a given starting index in a circular array of strings to a target string. The circular nature of the array means that moving past the end wraps around to the beginning, and moving before the first element wraps around to the last element. This is important because the...

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LeetCode 2586 - Count the Number of Vowel Strings in Range

LeetCode Problem 2586 Difficulty: 🟢 Easy Topics: Array, String, Counting Solution Problem Understanding The problem gives us an array of lowercase strings called words and two integer indices, left and right . We need to count how many strings within the inclusive range [left, right] are considered vowel strings. A string qualifies as a vowel string if both of these conditions are true: The first character is a vowel. The...

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LeetCode 2525 - Categorize Box According to Criteria

LeetCode Problem 2525 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem requires categorizing a box based on its dimensions and mass according to given criteria. We are given four integers: length , width , height , and mass . The output is a string that represents the category of the box: "Bulky" , "Heavy" , "Both" , or "Neither" . A box is "Bulky" if any dimension is...

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LeetCode 2643 - Row With Maximum Ones

LeetCode Problem 2643 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Here is the complete, detailed technical solution guide for LeetCode 2643 - Row With Maximum Ones following your exact formatting requirements. Problem Understanding The problem presents a binary matrix mat of size m x n , where each element is either 0 or 1 . The task is to identify the row that contains the maximum number of ones and...

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LeetCode 3340 - Check Balanced String

LeetCode Problem 3340 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string num that contains only numeric digits from '0' to '9' . We must determine whether the string is "balanced". A string is considered balanced when the sum of digits located at even indices is equal to the sum of digits located at odd indices. Indexing is zero-based, which means: Index 0 is even...

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LeetCode 2923 - Find Champion I

LeetCode Problem 2923 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding This problem describes a tournament of n teams, where every pair of teams has a clear winner. The input is given as a square matrix called grid , where grid[i][j] tells us whether team i is stronger than team j . If grid[i][j] == 1 , then team i defeats team j , meaning i is stronger. Since...

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LeetCode 3199 - Count Triplets with Even XOR Set Bits I

LeetCode Problem 3199 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem gives us three integer arrays, a , b , and c . We must count how many triplets (a[i], b[j], c[k]) produce a bitwise XOR result with an even number of set bits. A set bit is a bit equal to 1 in the binary representation of a number. For example: 5 in binary is...

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LeetCode 2888 - Reshape Data: Concatenate

LeetCode Problem 2888 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem is asking us to vertically concatenate two DataFrames into a single unified DataFrame. In simpler terms, given two tables df1 and df2 with identical columns and types, we need to stack the rows of df2 below the rows of df1 . The input consists of two pandas-like DataFrames, each with columns student_id , name , and age...

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LeetCode 2974 - Minimum Number Game

LeetCode Problem 2974 Difficulty: 🟢 Easy Topics: Array, Sorting, Heap (Priority Queue), Simulation Solution Problem Understanding The problem gives us an integer array nums with an even number of elements. We repeatedly simulate a game between Alice and Bob until the array becomes empty. In each round, the following sequence happens: Alice removes the smallest remaining number. Bob removes the next smallest remaining number. Bob appends his removed number to...

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LeetCode 2047 - Number of Valid Words in a Sentence

LeetCode Problem 2047 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to count the number of valid words in a sentence. The sentence consists of lowercase letters, digits, hyphens, punctuation ( ! , . , , ), and spaces. A word is defined as a token separated by spaces, and it is considered valid if it satisfies three conditions: It contains only lowercase letters, at most...

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LeetCode 2644 - Find the Maximum Divisibility Score

LeetCode Problem 2644 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to identify, from a list of divisors, the integer that has the maximum divisibility score with respect to a given array of numbers. The divisibility score of a divisor is defined as the count of elements in nums that are divisible by that divisor. In simpler terms, for each divisor, we count how many numbers...

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LeetCode 2068 - Check Whether Two Strings are Almost Equivalent

LeetCode Problem 2068 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks us to determine whether two strings are "almost equivalent" based on the frequency of each lowercase English letter. We are given two strings, word1 and word2 , both of the same length. For every character from 'a' to 'z' , we compare how many times that character appears in each string. If the...

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LeetCode 3062 - Winner of the Linked List Game

LeetCode Problem 3062 Difficulty: 🟢 Easy Topics: Linked List Solution Problem Understanding The problem gives us the head of a singly linked list whose length is always even. The nodes are grouped into pairs based on their indices: Nodes at indices (0, 1) form the first pair Nodes at indices (2, 3) form the second pair Nodes at indices (4, 5) form the third pair And so on Within each...

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LeetCode 2748 - Number of Beautiful Pairs

LeetCode Problem 2748 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Counting, Number Theory Solution LeetCode 2748 - Number of Beautiful Pairs Problem Understanding The problem gives us a 0-indexed integer array nums . We must count how many pairs of indices (i, j) satisfy 0 <= i < j < n and have the following property: Take the first digit of nums[i] . Take the last digit of nums[j]...

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LeetCode 2667 - Create Hello World Function

LeetCode Problem 2667 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to implement a function named createHelloWorld that returns another function. The returned function must always produce the string "Hello World" whenever it is called. The important detail is that the returned function may receive any number of arguments, including no arguments at all. Those arguments do not matter and should be completely ignored. Regardless of...

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LeetCode 1991 - Find the Middle Index in Array

LeetCode Problem 1991 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution LeetCode 1991 - Find the Middle Index in Array Problem Understanding The problem gives us a 0-indexed integer array called nums . We need to find an index such that the sum of all elements to the left of that index is equal to the sum of all elements to the right of that index. More formally, for an...

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LeetCode 3178 - Find the Child Who Has the Ball After K Seconds

LeetCode Problem 3178 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem asks us to simulate a game in which n children, numbered from 0 to n - 1 , stand in a straight line. Child 0 starts with a ball, and every second the child holding the ball passes it to the next child in the current direction. The direction is initially to the right, and it...

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LeetCode 2660 - Determine the Winner of a Bowling Game

LeetCode Problem 2660 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem describes a simplified scoring system for a bowling game between two players. Each player has an array representing the number of pins hit in each turn, and there are exactly n turns. Each turn normally scores the number of pins hit, but a bonus rule applies: if the player scored a strike (10 pins) in either...

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LeetCode 3370 - Smallest Number With All Set Bits

LeetCode Problem 3370 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation Solution Problem Understanding The problem asks us to find the smallest integer x such that: x >= n Every bit in the binary representation of x is set to 1 A number whose binary representation contains only set bits looks like this: 1 → binary "1" 3 → binary "11" 7 → binary "111" 15 → binary "1111" These numbers...

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LeetCode 2293 - Min Max Game

LeetCode Problem 2293 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding This problem asks us to repeatedly transform an array until only one number remains. At every round, we reduce the size of the array by half using alternating min and max operations on adjacent pairs. More specifically, we start with a 0-indexed array nums whose length is guaranteed to be a power of 2 . During each iteration,...

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LeetCode 1859 - Sorting the Sentence

LeetCode Problem 1859 Difficulty: 🟢 Easy Topics: String, Sorting Solution Problem Understanding The problem gives us a shuffled sentence , where every word has a number appended to its end. That number represents the word's original position in the sentence, using 1-indexed ordering . For example, the word "This1" means "This" originally appeared in position 1 , while "sentence4" means "sentence" originally appeared in position 4 . The words in...

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LeetCode 2815 - Max Pair Sum in an Array

LeetCode Problem 2815 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 2815 - Max Pair Sum in an Array Problem Understanding The problem gives us an array of integers nums . For every number, we can determine its largest digit . For example: 2536 has digits 2, 5, 3, 6 , so its largest digit is 6 112 has digits 1, 1, 2 , so its largest digit is...

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LeetCode 2725 - Interval Cancellation

LeetCode Problem 2725 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a function cancellable that repeatedly calls a given function fn with a set of arguments args at a fixed interval t milliseconds and allows this repeated execution to be stopped by a cancel function cancelFn . The first call to fn happens immediately (at time 0), and subsequent calls occur every t milliseconds....

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LeetCode 2677 - Chunk Array

LeetCode Problem 2677 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to split an input array into smaller subarrays, commonly called chunks , where each chunk has a fixed maximum size. In other words, given an array arr and an integer size , we need to partition the array into consecutive groups such that each subarray contains at most size elements. Every element from the original...

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LeetCode 2315 - Count Asterisks

LeetCode Problem 2315 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string s containing lowercase English letters, vertical bars '|' , and asterisks '*' . The key rule is that every two consecutive vertical bars form a pair. Any asterisk located between the two bars of a pair must be ignored when counting. Our task is to count only the asterisks that are outside these...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2520 - Count the Digits That Divide a Number

LeetCode Problem 2520 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine, given a positive integer num , how many of its digits evenly divide num . In other words, for each digit d in the number, we check if num % d == 0 . The input is a single integer between 1 and 10^9 , and the number will not contain a zero,...

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LeetCode 2099 - Find Subsequence of Length K With the Largest Sum

LeetCode Problem 2099 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Heap (Priority Queue) Solution Problem Understanding The problem asks us to find a subsequence of length k from a given integer array nums such that the sum of the elements in the subsequence is maximized. A subsequence is defined as a sequence that can be obtained from the original array by deleting zero or more elements without changing the...

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LeetCode 2460 - Apply Operations to an Array

LeetCode Problem 2460 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Simulation Solution LeetCode 2460 - Apply Operations to an Array Problem Understanding This problem gives us a 0-indexed array nums containing non-negative integers. We must perform a sequence of operations on adjacent elements, then rearrange the resulting array by moving all zeros to the end. The first phase consists of processing the array from left to right. For every index...

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LeetCode 2913 - Subarrays Distinct Element Sum of Squares I

LeetCode Problem 2913 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to examine every possible non-empty subarray of the given array nums . For each subarray, we compute how many distinct values appear inside it. After finding this distinct count, we square it and add it to the final answer. A subarray is contiguous, which means the elements must appear next to each other...

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LeetCode 3200 - Maximum Height of a Triangle

LeetCode Problem 3200 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 3200 - Maximum Height of a Triangle Problem Understanding The problem gives us two integers, red and blue , representing the number of red and blue balls available. We want to build a triangle where: Row 1 contains exactly 1 ball Row 2 contains exactly 2 balls Row 3 contains exactly 3 balls And so on There are two...

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LeetCode 3038 - Maximum Number of Operations With the Same Score I

LeetCode Problem 3038 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem asks us to repeatedly perform an operation on an integer array nums . In each operation, we remove the first two elements of the array and compute a score , which is simply the sum of those two removed values. The key restriction is that every operation must have the exact same score . We are...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2544 - Alternating Digit Sum

LeetCode Problem 2544 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to compute an alternating sum of the digits of a positive integer. The alternation starts from the most significant digit, which always has a positive sign. Every following digit flips the sign from the previous one. For example, if the number is 521 , the calculation becomes: +5 -2 +1 The final answer is 4...

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LeetCode 2062 - Count Vowel Substrings of a String

LeetCode Problem 2062 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem requires counting the number of vowel substrings in a given string word . A substring is any contiguous sequence of characters within the string. A vowel substring is defined as a substring that contains only vowels ( 'a' , 'e' , 'i' , 'o' , 'u' ) and must include all five vowels at least...

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LeetCode 3210 - Find the Encrypted String

LeetCode Problem 3210 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to implement a custom string encryption algorithm. We are given a string s and an integer k . For each character in s , we need to replace it with the character that is k positions ahead in the string, in a cyclic manner. "Cyclic" means that if the index goes beyond the end of...

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LeetCode 1979 - Find Greatest Common Divisor of Array

LeetCode Problem 1979 Difficulty: 🟢 Easy Topics: Array, Math, Number Theory Solution Problem Understanding The problem asks us to compute the greatest common divisor (GCD) of two specific values derived from the input array nums : the smallest element in the array and the largest element in the array. In other words, we are not computing the GCD of all elements, nor are we looking for pairwise relationships across the...

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LeetCode 3010 - Divide an Array Into Subarrays With Minimum Cost I

LeetCode Problem 3010 Difficulty: 🟢 Easy Topics: Array, Sorting, Enumeration Solution Problem Understanding The problem asks us to split a given array nums into exactly three disjoint contiguous subarrays and minimize the sum of their costs . The important detail is how cost is defined. The cost of a subarray is simply its first element . For example: [1,2,3] has cost 1 [10,5] has cost 10 Since we must divide...

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LeetCode 1873 - Calculate Special Bonus

LeetCode Problem 1873 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to write an SQL query that calculates a special bonus for every employee in the Employees table. Each row in the table contains three pieces of information: Column Meaning employee_id Unique identifier for the employee name Employee name salary Employee salary The task is to compute a new column called bonus according to two conditions:...

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LeetCode 2859 - Sum of Values at Indices With K Set Bits

LeetCode Problem 2859 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem asks us to compute the sum of elements in an array, but not based on the values themselves. Instead, we decide whether to include an element by examining the binary representation of its index . You are given a 0-indexed integer array nums and an integer k . For each index i in the array,...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2259 - Remove Digit From Number to Maximize Result

LeetCode Problem 2259 Difficulty: 🟢 Easy Topics: String, Greedy, Enumeration Solution LeetCode 2259 - Remove Digit From Number to Maximize Result Problem Understanding The problem gives us a string called number , which represents a positive integer, and a character digit , which is guaranteed to appear at least once inside number . Our task is to remove exactly one occurrence of digit from the string so that the resulting...

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LeetCode 2648 - Generate Fibonacci Sequence

LeetCode Problem 2648 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to implement a generator function that yields numbers from the Fibonacci sequence. The Fibonacci sequence is defined recursively as Xn = Xn-1 + Xn-2 with the starting values X0 = 0 and X1 = 1 . Essentially, each number in the sequence is the sum of the two preceding numbers. The input in this problem...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2160 - Minimum Sum of Four Digit Number After Splitting Digits

LeetCode Problem 2160 Difficulty: 🟢 Easy Topics: Math, Greedy, Sorting Solution Problem Understanding The problem asks us to take a four-digit integer num and split its digits into two new integers such that the sum of these two integers is minimized. We are allowed to use all digits exactly once, and the new integers can have leading zeros . For instance, if the number is 2932 , the digits are...

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LeetCode 2437 - Number of Valid Clock Times

LeetCode Problem 2437 Difficulty: 🟢 Easy Topics: String, Enumeration Solution Problem Understanding The problem asks us to determine the number of valid times that can be formed from a partially known digital clock string of the format "hh:mm" , where unknown digits are represented by '?' . Each '?' can be replaced with any digit from 0 to 9 , but the resulting hour ( hh ) must be in...

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LeetCode 2395 - Find Subarrays With Equal Sum

LeetCode Problem 2395 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to determine whether there exist two contiguous subarrays of length 2 in a given array nums that have the same sum. A subarray of length 2 is simply any consecutive pair of elements in the array. The two subarrays must begin at different indices, which means even if they have identical elements, they...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1965 - Employees With Missing Information

LeetCode Problem 1965 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides two relational tables, one named Employees and another named Salaries , both keyed by employee_id . Each employee may or may not appear in both tables. The Employees table contains the employee’s name, while the Salaries table contains the employee’s salary. The task is to identify all employee_id values for which information is incomplete. An employee...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1890 - The Latest Login in 2020

LeetCode Problem 1890 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table Logins that records user login events, with columns user_id and time_stamp . Each combination of (user_id, time_stamp) is unique, ensuring that every row corresponds to a distinct login. The task is to determine, for each user who logged in at least once during the year 2020, the latest login timestamp in that year...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1863 - Sum of All Subset XOR Totals

LeetCode Problem 1863 Difficulty: 🟢 Easy Topics: Array, Math, Backtracking, Bit Manipulation, Combinatorics, Enumeration Solution LeetCode 1863 - Sum of All Subset XOR Totals Problem Understanding This problem asks us to compute the sum of the XOR values of every possible subset of a given array. A subset is formed by choosing any combination of elements from the array, including the empty subset and the full array itself. Since an...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1903 - Largest Odd Number in String

LeetCode Problem 1903 Difficulty: 🟢 Easy Topics: Math, String, Greedy Solution Problem Understanding The problem asks us to find the largest-valued odd integer substring from a given string num that represents a large integer. Here, a substring is any contiguous sequence of characters in num . We must return the substring itself as a string, or an empty string if no odd number exists in num . For example, if...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2133 - Check if Every Row and Column Contains All Numbers

LeetCode Problem 2133 Difficulty: 🟢 Easy Topics: Array, Hash Table, Matrix Solution Problem Understanding In this problem, we are given an n x n matrix where every value is guaranteed to be between 1 and n . A matrix is considered valid if every row contains all integers from 1 through n exactly once, and every column also contains all integers from 1 through n exactly once. Another way to...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2794 - Create Object from Two Arrays

LeetCode Problem 2794 Difficulty: 🟢 Easy Topics: — Solution LeetCode 2794 - Create Object from Two Arrays Problem Understanding The problem provides two arrays, keysArr and valuesArr , which always have the same length. Each position in the arrays represents a potential key-value pair. The element at index i in keysArr should become the key, and the element at index i in valuesArr should become the corresponding value. The goal...

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LeetCode 1957 - Delete Characters to Make Fancy String

LeetCode Problem 1957 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to transform a given string into a "fancy string". A fancy string is defined as a string that does not contain three consecutive identical characters anywhere in the string. We are allowed to delete characters from the original string, and our goal is to delete as few characters as possible. After performing the minimum deletions,...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2715 - Timeout Cancellation

LeetCode Problem 2715 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a cancellable delayed function execution mechanism. Essentially, you are given a function fn , an array of arguments args , and a timeout t in milliseconds. Your task is to return a cancel function cancelFn that, when invoked, can prevent the execution of fn if it has not already occurred. The function fn...

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LeetCode 2760 - Longest Even Odd Subarray With Threshold

LeetCode Problem 2760 Difficulty: 🟢 Easy Topics: Array, Sliding Window Solution Problem Understanding The problem asks us to find the length of the longest contiguous subarray in a given integer array nums that satisfies three specific conditions. First, the subarray must start with an even number. Second, the subarray must alternate between even and odd numbers throughout its length. Third, every number in the subarray must be less than or...

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LeetCode 1984 - Minimum Difference Between Highest and Lowest of K Scores

LeetCode Problem 1984 Difficulty: 🟢 Easy Topics: Array, Sliding Window, Sorting Solution Problem Understanding The problem asks us to find the minimum possible difference between the highest and lowest scores when selecting exactly k scores from an array of student scores. The input is a 0-indexed integer array nums where each element represents a student's score, and an integer k which is the number of scores to pick. The expected...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2666 - Allow One Function Call

LeetCode Problem 2666 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to create a wrapper around an existing function fn such that the wrapped version can only execute the original function one time. In other words, we are given a function fn , and we must return a new function. This returned function behaves exactly like fn during its first invocation, meaning it accepts the same...

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LeetCode 2778 - Sum of Squares of Special Elements

LeetCode Problem 2778 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding This problem asks us to compute the sum of squares of certain elements in an array, specifically the special elements . The array nums is 1-indexed , meaning the first element is at index 1 (not 0). An element nums[i] is considered special if its 1-based index divides the length of the array n exactly. In other words,...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2103 - Rings and Rods

LeetCode Problem 2103 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem is asking us to determine how many rods, labeled from 0 to 9, have all three colors of rings placed on them. Each ring is described by a two-character string: the first character is the color ( 'R' for red, 'G' for green, 'B' for blue) and the second character is the rod index (...

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LeetCode 2085 - Count Common Words With One Occurrence

LeetCode Problem 2085 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Counting Solution LeetCode 2085, Count Common Words With One Occurrence Problem Understanding This problem gives us two arrays of strings, words1 and words2 . Our task is to count how many strings appear exactly once in both arrays. The key detail is that a word only qualifies if: It appears exactly one time in words1 It appears exactly one...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2409 - Count Days Spent Together

LeetCode Problem 2409 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to calculate the number of days Alice and Bob spend together in Rome based on their respective arrival and departure dates. Each date is represented as a string in the format "MM-DD" . The input consists of four strings: arriveAlice , leaveAlice , arriveBob , and leaveBob . The output should be the total...

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LeetCode 3396 - Minimum Number of Operations to Make Elements in Array Distinct

LeetCode Problem 3396 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem gives us an integer array nums , and our goal is to make all remaining elements distinct. The only allowed operation is removing exactly 3 elements from the beginning of the array. If fewer than 3 elements remain, we remove everything that is left. We need to determine the minimum number of such operations required...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2652 - Sum Multiples

LeetCode Problem 2652 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem requires calculating the sum of all integers from 1 up to a given positive integer n that are divisible by 3, 5, or 7. In simpler terms, we need to consider each number in the range [1, n] and check if it is a multiple of any of these three numbers. If it is, we include it...

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LeetCode 3285 - Find Indices of Stable Mountains

LeetCode Problem 3285 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to find indices of "stable" mountains from a given array of mountain heights. Each element in the array represents the height of a mountain in sequence. A mountain is stable if the mountain immediately before it exists and has a height strictly greater than a given threshold. Notably, the first mountain at index 0 cannot...

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LeetCode 2804 - Array Prototype ForEach

LeetCode Problem 2804 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a custom version of the forEach method for arrays in JavaScript. The goal is to extend the Array.prototype so that any array can call forEach(callback, context) and execute the callback on each element. The callback function receives three parameters: the current element value, its index, and the array itself. Additionally, the optional context...

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LeetCode 2678 - Number of Senior Citizens

LeetCode Problem 2678 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding This problem asks us to count the number of passengers in a list who are strictly older than 60. Each passenger's information is compressed into a fixed-length string of 15 characters. The string is structured as follows: the first ten characters represent the phone number, the eleventh character represents gender, the twelfth and thirteenth characters represent the age,...

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LeetCode 2985 - Calculate Compressed Mean

LeetCode Problem 2985 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the average number of items per order from a compressed representation of order data. Instead of storing every individual order as a separate row, the table groups together orders that contain the same number of items. For each row: item_count represents how many items are in a particular type of order. order_occurrences represents...

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LeetCode 2670 - Find the Distinct Difference Array

LeetCode Problem 2670 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to compute the distinct difference array for a given integer array nums . For each index i in the array, we calculate the difference between the number of distinct elements in the prefix nums[0, ..., i] and the number of distinct elements in the suffix nums[i + 1, ..., n - 1] ....

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LeetCode 3019 - Number of Changing Keys

LeetCode Problem 3019 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to determine how many times a user changes keys while typing a string s . A change of key occurs when the current character typed differs in its lowercase form from the previous character typed. Importantly, differences in case (uppercase vs lowercase) do not count as a key change because modifiers like shift or caps...

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LeetCode 1995 - Count Special Quadruplets

LeetCode Problem 1995 Difficulty: 🟢 Easy Topics: Array, Hash Table, Enumeration Solution Problem Understanding The problem asks us to count the number of distinct quadruplets (a, b, c, d) in a given array nums such that the sum of the first three elements equals the fourth, i.e., nums[a] + nums[b] + nums[c] == nums[d] , and the indices satisfy a < b < c < d . In simpler terms,...

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LeetCode 3079 - Find the Sum of Encrypted Integers

LeetCode Problem 3079 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem provides an array of positive integers nums and asks us to compute a sum based on an encryption transformation. The transformation encrypt(x) replaces every digit in x with the largest digit in x . For example, encrypt(523) results in 555 because the largest digit in 523 is 5 , and every digit is replaced by 5...

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LeetCode 3330 - Find the Original Typed String I

LeetCode Problem 3330 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to determine the number of possible original strings Alice intended to type based on the final string displayed on her screen. Alice might have accidentally pressed a key too long at most once , resulting in one sequence of consecutive repeated characters appearing longer than intended. The input is a string word representing the final...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2784 - Check if Array is Good

LeetCode Problem 2784 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem defines a special type of array called a "good" array. A good array must be a permutation of: $$base[n] = [1, 2, 3, ..., n-1, n, n]$$ This means the array must contain: Every integer from 1 to n - 1 exactly once The integer n exactly twice No other numbers Total length equal...

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LeetCode 2620 - Counter

LeetCode Problem 2620 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem is asking us to implement a simple counter function with a closure-like behavior. Given an integer n , we need to return a function counter() that, when called the first time, returns n , and then increments the returned value by one for every subsequent call. Essentially, each call to the counter() function should produce a sequence...

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LeetCode 3042 - Count Prefix and Suffix Pairs I

LeetCode Problem 3042 Difficulty: 🟢 Easy Topics: Array, String, Trie, Rolling Hash, String Matching, Hash Function Solution LeetCode 3042 - Count Prefix and Suffix Pairs I Problem Understanding The problem gives us an array of strings called words . For every pair of indices (i, j) where i < j , we must determine whether words[i] is both a prefix and a suffix of words[j] . A string is a...

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LeetCode 2839 - Check if Strings Can be Made Equal With Operations I

LeetCode Problem 2839 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us two strings, s1 and s2 , each containing exactly four lowercase English letters. We are allowed to repeatedly perform a very specific swap operation on either string. In one operation, we may choose two indices i and j such that j - i = 2 , then swap the characters at those positions. Because the...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1832 - Check if the Sentence Is Pangram

LeetCode Problem 1832 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding This problem asks us to determine whether a given string is a pangram. A pangram is a sentence that contains every lowercase English letter, from 'a' through 'z' , at least once. The input is a single string named sentence . The problem guarantees that the string contains only lowercase English letters, which simplifies the implementation because...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2446 - Determine if Two Events Have Conflict

LeetCode Problem 2446 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to determine if two events on the same day overlap in time. Each event is given as a pair of strings in HH:MM format representing the start and end times. The output should be a boolean: true if there is any overlap between the two events, and false otherwise. The input guarantees that the...

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LeetCode 3289 - The Two Sneaky Numbers of Digitville

LeetCode Problem 3289 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math Solution Problem Understanding The problem is asking us to identify two numbers that appear twice in an otherwise consecutive list of integers ranging from 0 to n - 1 . In other words, the input nums is almost a permutation of the numbers 0 through n - 1 , except that two numbers are repeated , so the length...

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LeetCode 2765 - Longest Alternating Subarray

LeetCode Problem 2765 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 2765 - Longest Alternating Subarray Problem Understanding This problem asks us to find the longest contiguous subarray that follows a very specific alternating pattern. Given an integer array nums , we need to identify subarrays where: The subarray length is at least 2 . The second element is exactly one greater than the first element. Every subsequent difference alternates...

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LeetCode 1869 - Longer Contiguous Segments of Ones than Zeros

LeetCode Problem 1869 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a binary string s , which means the string contains only the characters '0' and '1' . We need to determine whether the longest contiguous sequence of 1 s is strictly longer than the longest contiguous sequence of 0 s. A contiguous segment means consecutive characters without interruption. For example, in the string "1110011" :...

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LeetCode 2723 - Add Two Promises

LeetCode Problem 2723 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to work with JavaScript promises and asynchronous execution. We are given two promises, promise1 and promise2 , and each promise is guaranteed to eventually resolve to a numeric value. Our task is to return a new promise that resolves to the sum of the two resolved values. In simpler terms, imagine two asynchronous operations are...

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LeetCode 2717 - Semi-Ordered Permutation

LeetCode Problem 2717 Difficulty: 🟢 Easy Topics: Array, Simulation Solution LeetCode 2717 - Semi-Ordered Permutation Problem Understanding The problem gives us a permutation nums of length n . A permutation means the array contains every integer from 1 to n exactly once. A permutation is considered semi-ordered when: The first element is 1 The last element is n We are allowed to repeatedly swap adjacent elements. Each adjacent swap counts...

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LeetCode 2465 - Number of Distinct Averages

LeetCode Problem 2465 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Sorting Solution Problem Understanding The problem requires calculating the number of distinct averages generated from a sequence of numbers using a specific process. The input is an integer array nums of even length. The process repeatedly removes the smallest and largest numbers from the array, calculates their average, and continues until the array is empty. The output is...

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LeetCode 3238 - Find the Number of Winning Players

LeetCode Problem 3238 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution LeetCode 3238 - Find the Number of Winning Players Problem Understanding The problem gives us n players and a list called pick , where each entry is of the form [xi, yi] . This means player xi picked a ball with color yi . A player wins if they have picked strictly more than their player index number...

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LeetCode 2481 - Minimum Cuts to Divide a Circle

LeetCode Problem 2481 Difficulty: 🟢 Easy Topics: Math, Geometry Solution Problem Understanding The problem asks for the minimum number of straight cuts required to divide a circle into n equal slices . A valid cut can either pass through the center and touch two points on the circle, or touch one point on the circle and pass through the center. The input is a single integer n representing the desired...

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LeetCode 2882 - Drop Duplicate Rows

LeetCode Problem 2882 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem asks us to process a DataFrame representing customers and remove rows that have duplicate email addresses. Specifically, if multiple rows share the same email value, only the first occurrence should be kept, and all subsequent duplicates should be discarded. The input is a structured table with columns customer_id , name , and email . Each row represents...

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LeetCode 2690 - Infinite Method Object

LeetCode Problem 2690 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding This problem asks us to implement a function that returns an infinite-method object . The defining property of this object is that any method name can be accessed and called , and when invoked, it should return the exact name of the method. For example, if we create an object like this: const obj = createInfiniteObject(); Then calling: obj.hello()...

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LeetCode 2881 - Create a New Column

LeetCode Problem 2881 Difficulty: 🟢 Easy Topics: — Solution Problem Understanding The problem is asking us to modify a given DataFrame named employees by adding a new column called bonus . Each value in the bonus column should be exactly double the corresponding value in the salary column. The input DataFrame contains at least two columns: name , which is a string representing the employee's name, and salary , which...

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LeetCode 3059 - Find All Unique Email Domains

LeetCode Problem 3059 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to analyze email addresses stored in a database table and determine how many people belong to each unique email domain, but only for domains ending in .com . The Emails table contains two columns: Column Meaning id Unique identifier for each row email Full email address An email address has the general structure: username@domain For...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3314 - Construct the Minimum Bitwise Array I

LeetCode Problem 3314 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem asks us to construct an array ans from a given array nums of prime integers. For each element nums[i] , we need to find the smallest integer ans[i] such that the bitwise OR of ans[i] and ans[i] + 1 equals nums[i] . Formally, ans[i] | (ans[i] + 1) == nums[i] . If no such ans[i]...

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LeetCode 2582 - Pass the Pillow

LeetCode Problem 2582 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem describes a line of n people, numbered sequentially from 1 to n . Initially, person 1 holds a pillow. Every second, the pillow is passed to the adjacent person. The direction of passing changes whenever the pillow reaches either end of the line. In other words, the pillow moves forward from person 1 toward person n...

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LeetCode 3232 - Find if Digit Game Can Be Won

LeetCode Problem 3232 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem presents a simple two-player game between Alice and Bob using an array of positive integers. Each number in the array is either a single-digit number (1 to 9) or a double-digit number (10 to 99). Alice has the choice to select either all single-digit numbers or all double-digit numbers from the array, while Bob automatically gets...

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LeetCode 3127 - Make a Square with the Same Color

LeetCode Problem 3127 Difficulty: 🟢 Easy Topics: Array, Matrix, Enumeration Solution Problem Understanding This problem gives us a fixed 3 x 3 grid containing only two possible characters, 'B' for black and 'W' for white. We are allowed to change the color of at most one cell. The goal is to determine whether, after performing zero or one modification, the grid can contain at least one 2 x 2 subgrid...

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LeetCode 3024 - Type of Triangle

LeetCode Problem 3024 Difficulty: 🟢 Easy Topics: Array, Math, Sorting Solution Problem Understanding The problem gives an integer array nums of length 3 , where each value represents the length of a side of a possible triangle. Our task is to determine what kind of triangle these three sides can form. There are four possible outputs: "equilateral" if all three sides are equal "isosceles" if exactly two sides are equal...

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LeetCode 2319 - Check if Matrix Is X-Matrix

LeetCode Problem 2319 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem gives us a square matrix grid of size n x n . We must determine whether this matrix satisfies the definition of an X-Matrix. An X-Matrix has a very specific structure. The two diagonals of the matrix must contain only non-zero values, and every other position must contain exactly 0 . The two diagonals are: The...

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LeetCode 234 - Palindrome Linked List

LeetCode Problem 234 Difficulty: 🟢 Easy Topics: Linked List, Two Pointers, Stack, Recursion Solution Problem Understanding The problem gives us the head of a singly linked list and asks whether the sequence of values stored in the list forms a palindrome. A palindrome is a sequence that reads the same forward and backward. For example, the array [1,2,2,1] is a palindrome because reversing it produces the same sequence. On the...

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LeetCode 268 - Missing Number

LeetCode Problem 268 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting Solution Problem Understanding The problem gives an array nums containing n distinct integers. Every number is supposed to come from the range [0, n] , which means there are actually n + 1 possible values in total. Since the array only contains n numbers, exactly one value from that range is missing. The task...

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LeetCode 1796 - Second Largest Digit in a String

LeetCode Problem 1796 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem gives us a string s that contains lowercase English letters and numerical digits. Our task is to find the second largest distinct digit that appears anywhere in the string. The important detail is that we care about distinct digits, not frequency. If the string contains "111222333" , the distinct digits are {1, 2, 3} ....

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LeetCode 824 - Goat Latin

LeetCode Problem 824 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to transform a given sentence into a fictional language called Goat Latin , following a specific set of string manipulation rules. The input is a string called sentence , where words are separated by a single space. Every word contains only English alphabetic characters, meaning uppercase and lowercase letters. We must process each word individually...

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LeetCode 1119 - Remove Vowels from a String

LeetCode Problem 1119 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to remove vowels from a given string s . Specifically, the vowels are defined as the lowercase characters 'a' , 'e' , 'i' , 'o' , and 'u' . The input string consists only of lowercase English letters, and its length ranges from 1 to 1000. The expected output is a string that contains all...

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LeetCode 422 - Valid Word Square

LeetCode Problem 422 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem asks us to determine whether a given list of strings forms a valid word square . A word square is a special arrangement of words such that the kth row and the kth column contain the same sequence of letters for every valid index k . Essentially, if you read the words horizontally as rows and...

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LeetCode 1266 - Minimum Time Visiting All Points

LeetCode Problem 1266 Difficulty: 🟢 Easy Topics: Array, Math, Geometry Solution LeetCode 1266 - Minimum Time Visiting All Points Problem Understanding The problem gives a sequence of points on a 2D coordinate plane. Each point is represented as [x, y] , where x and y are integer coordinates. Your task is to determine the minimum number of seconds required to visit every point in the exact order they appear in...

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LeetCode 94 - Binary Tree Inorder Traversal

LeetCode Problem 94 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Tree Solution Binary Tree Inorder Traversal Problem Understanding This problem asks us to perform an inorder traversal on a binary tree and return the values of the visited nodes in the correct order. A binary tree is a hierarchical data structure where each node can have at most two children, a left child and a right child. The...

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LeetCode 2037 - Minimum Number of Moves to Seat Everyone

LeetCode Problem 2037 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting, Counting Sort Solution Problem Understanding This problem asks us to assign students to seats such that every student occupies exactly one seat and no two students share the same seat. Each student can move left or right on a number line, and every movement by one position costs exactly one move. The goal is to minimize the total number of...

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LeetCode 577 - Employee Bonus

LeetCode Problem 577 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding In this problem, we are given two database tables, Employee and Bonus , and we need to produce a result table containing employees who meet one of two conditions: Their bonus is less than 1000 . They do not have a bonus record at all. The output should include only two columns: the employee's name and their bonus ....

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LeetCode 110 - Balanced Binary Tree

LeetCode Problem 110 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to determine whether a given binary tree is height-balanced . A binary tree is considered height-balanced if, for every node in the tree, the height difference between its left and right subtrees is at most 1 . In simpler terms, the tree should not be heavily skewed to one side at...

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LeetCode 1317 - Convert Integer to the Sum of Two No-Zero Integers

LeetCode Problem 1317 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to split a given integer n into two positive integers a and b such that: a + b = n Neither a nor b contains the digit 0 anywhere in their decimal representation Such integers are called No-Zero integers . The input is a single integer n , and the output should be a list...

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LeetCode 1150 - Check If a Number Is Majority Element in a Sorted Array

LeetCode Problem 1150 Difficulty: 🟢 Easy Topics: Array, Binary Search Solution Problem Understanding This problem asks us to determine if a given target integer is a majority element in a sorted array nums . A majority element is defined as an element that appears more than half of the array's length . In other words, if nums.length is n , a majority element occurs strictly more than n / 2...

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LeetCode 492 - Construct the Rectangle

LeetCode Problem 492 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem gives us a single integer, area , which represents the area of a rectangle. Our task is to find two integers: L , the length W , the width such that: L * W == area L >= W L - W is as small as possible In other words, among all valid factor pairs of area...

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LeetCode 1640 - Check Array Formation Through Concatenation

LeetCode Problem 1640 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 1640 - Check Array Formation Through Concatenation Problem Understanding This problem gives us two inputs: arr , a one-dimensional array of distinct integers pieces , a collection of smaller integer arrays The goal is to determine whether we can recreate arr by concatenating the arrays inside pieces in any order. The important restriction is that we are not...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 495 - Teemo Attacking

LeetCode Problem 495 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem asks us to calculate the total duration that Ashe is poisoned by Teemo's attacks. Each attack at a given second t causes Ashe to be poisoned for exactly duration seconds, and the poisoning time is inclusive , meaning that the poison effect lasts from time t to t + duration - 1 . If Teemo attacks...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1141 - User Activity for the Past 30 Days I

LeetCode Problem 1141 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 1141 - User Activity for the Past 30 Days I Problem Understanding This problem asks us to compute the number of distinct active users for each day within a fixed 30 day window. The window ends on 2019-07-27 , inclusive, which means we only consider activity dates from 2019-06-28 through 2019-07-27 . The Activity table records user interactions on a...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1142 - User Activity for the Past 30 Days II

LeetCode Problem 1142 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the average number of sessions per user over a specific 30-day period ending on 2019-07-27 . Each row in the Activity table represents an activity a user performed in a session on a particular date. A single session can have multiple activities, and the table may contain duplicate rows. A session counts for...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1633 - Percentage of Users Attended a Contest

LeetCode Problem 1633 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the percentage of users who attended each contest . We are given two tables: Users and Register . The Users table contains all users, each with a unique user_id . The Register table contains records of which user registered for which contest, using contest_id and user_id . The goal is to compute the...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1550 - Three Consecutive Odds

LeetCode Problem 1550 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding This problem asks us to examine a list of integers, arr , and determine whether there exists a sequence of three consecutive odd numbers anywhere in the array. In simpler terms, we need to scan the array from left to right and check if at any point three numbers in a row are all odd. If such a sequence...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1805 - Number of Different Integers in a String

LeetCode Problem 1805 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem requires us to process a string word that contains both lowercase English letters and digits. We are asked to extract all the sequences of digits as integers, ignoring any non-digit characters. After extracting these sequences, we need to count how many unique integers exist, considering that integers with leading zeros are equivalent to their non-zero...

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LeetCode 905 - Sort Array By Parity

LeetCode Problem 905 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Sorting Solution Problem Understanding The problem asks us to rearrange an array so that all even numbers appear before all odd numbers. The relative ordering among even numbers does not matter, and the relative ordering among odd numbers also does not matter. The problem explicitly states that any valid arrangement is acceptable. We are given an integer array nums ....

Practice › LeetCode › LeetCode 02xx ›

LeetCode 243 - Shortest Word Distance

LeetCode Problem 243 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem gives us an array of strings called wordsDict , along with two distinct target words, word1 and word2 . Both target words are guaranteed to exist somewhere in the array. Our goal is to compute the smallest distance between any occurrence of word1 and any occurrence of word2 . The distance between two words is defined...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 604 - Design Compressed String Iterator

LeetCode Problem 604 Difficulty: 🟢 Easy Topics: Array, String, Design, Iterator Solution Problem Understanding This problem asks us to implement a compressed string iterator . We are given a string where each character is immediately followed by a number representing how many times that character appears consecutively in the uncompressed version. For example, "a3b2" represents "aaabb" . We are required to implement a class StringIterator with two methods: next() ,...

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LeetCode 1528 - Shuffle String

LeetCode Problem 1528 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to take a string s and an integer array indices of the same length, and produce a new string where each character in s is moved to the position specified by indices . In other words, for each index i in s , the character s[i] should be placed at position indices[i] in the...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1732 - Find the Highest Altitude

LeetCode Problem 1732 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution Problem Understanding In this problem, a biker starts at altitude 0 and travels through a sequence of roads. The input array gain describes how the biker's altitude changes between consecutive points on the trip. If gain[i] is positive, the biker climbs upward between point i and point i + 1 . If it is negative, the biker descends. The...

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LeetCode 1784 - Check if Binary String Has at Most One Segment of Ones

LeetCode Problem 1784 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding In this problem, we are given a binary string s that contains only the characters '0' and '1' . The string is guaranteed to begin with '1' , which means there are no leading zeros. The task is to determine whether the string contains at most one contiguous segment of ones. A contiguous segment of ones means a sequence...

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LeetCode 1175 - Prime Arrangements

LeetCode Problem 1175 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to count how many permutations of numbers from 1 to n satisfy a specific condition: all prime numbers must appear at prime-numbered indices (1-indexed). For instance, in the permutation [1,2,5,4,3] for n = 5 , the primes 2, 3, and 5 appear at indices 2, 3, and 5 respectively, all of which are prime positions,...

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LeetCode 1213 - Intersection of Three Sorted Arrays

LeetCode Problem 1213 Difficulty: 🟢 Easy Topics: Array, Hash Table, Binary Search, Counting Solution Problem Understanding The problem gives us three integer arrays, arr1 , arr2 , and arr3 . Each array is already sorted in strictly increasing order. Strictly increasing means there are no duplicate values inside the same array, and every next element is larger than the previous one. Our task is to return a new sorted array...

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LeetCode 1252 - Cells with Odd Values in a Matrix

LeetCode Problem 1252 Difficulty: 🟢 Easy Topics: Array, Math, Simulation Solution Problem Understanding The problem gives us an m x n matrix where every cell initially contains 0 . We are also given a list called indices , where each element is a pair [ri, ci] . For every pair [ri, ci] , we must perform two operations: Increment every value in row ri by 1 Increment every value in...

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LeetCode 387 - First Unique Character in a String

LeetCode Problem 387 Difficulty: 🟢 Easy Topics: Hash Table, String, Queue, Counting Solution Problem Understanding The problem gives us a string s consisting only of lowercase English letters. We must find the index of the first character that appears exactly once in the entire string. If every character appears more than once, we return -1 . The key detail is that we are looking for the first non-repeating character based...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 733 - Flood Fill

LeetCode Problem 733 Difficulty: 🟢 Easy Topics: Array, Depth-First Search, Breadth-First Search, Matrix Solution Problem Understanding The problem is asking us to simulate a flood fill operation on a 2D grid that represents an image. Each cell in the grid contains an integer representing a pixel color. You are given a starting pixel (sr, sc) and a target color color . The goal is to change the color of the...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 645 - Set Mismatch

LeetCode Problem 645 Difficulty: 🟢 Easy Topics: Array, Hash Table, Bit Manipulation, Sorting Solution Problem Understanding The problem describes a corrupted set of integers. Originally, the set contained every number from 1 through n exactly once. Because of an error, one number was duplicated, which means one other number disappeared. The input array nums represents this corrupted version of the set. Since one number appears twice and another is missing,...

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LeetCode 706 - Design HashMap

LeetCode Problem 706 Difficulty: 🟢 Easy Topics: Array, Hash Table, Linked List, Design, Hash Function Solution Problem Understanding The problem requires us to implement a HashMap from scratch without using any built-in hash table libraries. In other words, we need to create a data structure that can store key-value pairs, allow efficient insertion, retrieval, and deletion of values based on their keys. The input operations consist of put , get...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1009 - Complement of Base 10 Integer

LeetCode Problem 1009 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding This problem asks us to compute the complement of a base-10 integer by flipping every bit in its binary representation. For instance, if the input n is 5, its binary form is 101 . Flipping each 0 to 1 and each 1 to 0 produces 010 , which equals 2 in decimal. The input is guaranteed to be...

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LeetCode 349 - Intersection of Two Arrays

LeetCode Problem 349 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Binary Search, Sorting Solution Problem Understanding The problem gives us two integer arrays, nums1 and nums2 , and asks us to return their intersection. The intersection consists of all values that appear in both arrays. However, the result must contain only unique elements, even if a number appears many times in either array. For example, if nums1 =...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 896 - Monotonic Array

LeetCode Problem 896 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding This problem asks us to determine whether a given array of integers is monotonic. An array is considered monotonic if it is entirely non-decreasing (monotone increasing) or entirely non-increasing (monotone decreasing). In simpler terms, as we traverse the array from left to right, the elements should either never decrease or never increase. The input is a single list of...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 566 - Reshape the Matrix

LeetCode Problem 566 Difficulty: 🟢 Easy Topics: Array, Matrix, Simulation Solution Problem Understanding The problem is asking us to take an existing m x n matrix and "reshape" it into a new matrix with r rows and c columns. Reshaping means rearranging the elements in the matrix in row-major order (left-to-right, top-to-bottom) without changing the order of the elements themselves. If the number of elements in the original matrix (...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1527 - Patients With a Condition

LeetCode Problem 1527 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to query a database table Patients and return the records of patients who have Type I Diabetes. Each patient record includes a patient_id , patient_name , and a conditions column. The conditions column may contain zero or more condition codes separated by spaces. A patient has Type I Diabetes if any of their condition codes...

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LeetCode 543 - Diameter of Binary Tree

LeetCode Problem 543 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to compute the diameter of a binary tree. The diameter is defined as the length of the longest path between any two nodes , measured in number of edges. Importantly, this path does not need to pass through the root of the tree. In other words, the path can lie entirely...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 914 - X of a Kind in a Deck of Cards

LeetCode Problem 914 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Counting, Number Theory Solution Problem Understanding The problem asks whether it is possible to partition a deck of cards, represented as an integer array deck , into groups such that each group contains exactly x cards, all of which have the same integer value, and x is greater than 1. Essentially, we need to find a number x that...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 401 - Binary Watch

LeetCode Problem 401 Difficulty: 🟢 Easy Topics: Backtracking, Bit Manipulation Solution Problem Understanding The problem describes a binary watch that uses LEDs to represent time. The watch has two sections. The top section contains 4 LEDs for the hour, and the bottom section contains 6 LEDs for the minutes. Each LED represents a binary digit. If an LED is on, it contributes its corresponding binary value. The hour LEDs can...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 551 - Student Attendance Record I

LeetCode Problem 551 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string s where each character represents a student's attendance record for one day. There are only three possible characters: 'A' means the student was absent. 'L' means the student was late. 'P' means the student was present. We must determine whether the student qualifies for an attendance award. The student is eligible only if...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 977 - Squares of a Sorted Array

LeetCode Problem 977 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Sorting Solution Problem Understanding The problem asks us to take an array of integers nums that is already sorted in non-decreasing order and return a new array containing the squares of each number , also sorted in non-decreasing order. In simpler terms, we first transform every number x in the array to x * x , and then we produce...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2026 - Low-Quality Problems

LeetCode Problem 2026 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Problems . Each row represents a LeetCode problem and contains three columns: Column Meaning problem_id Unique identifier for the problem likes Number of users who liked the problem dislikes Number of users who disliked the problem We must identify all problems whose like percentage is strictly less than 60% . The...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 246 - Strobogrammatic Number

LeetCode Problem 246 Difficulty: 🟢 Easy Topics: Hash Table, Two Pointers, String Solution Problem Understanding The problem asks us to determine whether a given numeric string remains valid and unchanged when rotated 180 degrees. This property is called being "strobogrammatic". A strobogrammatic number is formed only by digits that still represent valid digits after rotation. The valid transformations are: 0 -> 0 1 -> 1 6 -> 9 8 ->...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1221 - Split a String in Balanced Strings

LeetCode Problem 1221 Difficulty: 🟢 Easy Topics: String, Greedy, Counting Solution LeetCode 1221 - Split a String in Balanced Strings Problem Understanding This problem gives us a string s that contains only the characters 'L' and 'R' . The string is guaranteed to already be balanced overall, meaning the total number of 'L' characters equals the total number of 'R' characters. Our task is to split this string into the...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 603 - Consecutive Available Seats

LeetCode Problem 603 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Cinema with two columns: Column Meaning seat_id Unique identifier for a seat free Whether the seat is available, where 1 means free and 0 means occupied We need to find all seats that are part of at least one consecutive sequence of free seats. Two seats are consecutive if their seat_id...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1071 - Greatest Common Divisor of Strings

LeetCode Problem 1071 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to find the greatest common divisor (GCD) of two strings. In this context, a string t divides another string s if s can be formed by concatenating t multiple times. The goal is to find the largest string x that divides both str1 and str2 . The input consists of two non-empty strings, str1...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1408 - String Matching in an Array

LeetCode Problem 1408 Difficulty: 🟢 Easy Topics: Array, String, String Matching Solution You included two different problems in one message, and the second problem (LeetCode 1408) appears to replace the first one while repeating the formatting instructions. I will proceed with LeetCode 1408 - String Matching in an Array . Problem Understanding The problem gives us an array of unique strings called words . We need to find every string...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 290 - Word Pattern

LeetCode Problem 290 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem gives two inputs: a pattern string and a space-separated string of words. We need to determine whether the sequence of words follows the same structure as the sequence of characters in the pattern. A valid match requires a bijection between pattern characters and words. A bijection means the mapping works in both directions: Each character...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1581 - Customer Who Visited but Did Not Make Any Transactions

LeetCode Problem 1581 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us two database tables, Visits and Transactions . The Visits table records every time a customer visited the mall. Each row contains a unique visit_id and the customer_id associated with that visit. The Transactions table records purchases made during a visit. Each transaction references a visit_id , meaning that a single visit can have zero, one,...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1076 - Project Employees II

LeetCode Problem 1076 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify the project or projects that have the largest number of employees assigned to them. We are given two database tables. The Project table stores relationships between projects and employees. Each row means that a particular employee is working on a particular project. The pair (project_id, employee_id) is unique, which guarantees that the same...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1757 - Recyclable and Low Fat Products

LeetCode Problem 1757 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem gives us a database table named Products . Each row represents a product and contains three columns: Column Meaning product_id Unique identifier for the product low_fats 'Y' if the product is low fat, otherwise 'N' recyclable 'Y' if the product is recyclable, otherwise 'N' The task is to return the IDs of products that satisfy both conditions...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1763 - Longest Nice Substring

LeetCode Problem 1763 Difficulty: 🟢 Easy Topics: Hash Table, String, Divide and Conquer, Bit Manipulation, Sliding Window Solution Problem Understanding The problem asks us to find the longest "nice" substring within a given string s . A substring is considered nice if for every letter it contains, both its lowercase and uppercase forms appear. For example, "aAa" is nice because it contains 'a' and 'A' . Conversely, "abA" is not...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 806 - Number of Lines To Write String

LeetCode Problem 806 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding This problem is asking us to determine how to write a string s on multiple lines when each character has a specific pixel width and no line can exceed 100 pixels. We are given an array widths of length 26, where each index corresponds to a lowercase English letter, and its value indicates how many pixels wide that...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 219 - Contains Duplicate II

LeetCode Problem 219 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sliding Window Solution Problem Understanding The problem asks us to determine whether an array contains two equal values whose indices are close to each other. More specifically, we need to check if there exist two distinct indices i and j such that: nums[i] == nums[j] abs(i - j) <= k The array nums contains integers, and k defines the maximum...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1637 - Widest Vertical Area Between Two Points Containing No Points

LeetCode Problem 1637 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding This problem gives us a list of points on a 2D plane, where each point is represented as [x, y] . We need to find the widest vertical area that contains no points strictly inside it. A vertical area is defined by two vertical lines. Since the area extends infinitely along the y-axis, only the x-coordinates matter. The...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 455 - Assign Cookies

LeetCode Problem 455 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Greedy, Sorting Solution LeetCode 455, Assign Cookies Problem Understanding This problem asks us to maximize the number of children who can be satisfied with the available cookies. Each child has a greed factor, and each cookie has a size. A child becomes content only if they receive a cookie whose size is greater than or equal to their greed factor....

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1290 - Convert Binary Number in a Linked List to Integer

LeetCode Problem 1290 Difficulty: 🟢 Easy Topics: Linked List, Math Solution Problem Understanding The problem gives us the head of a singly linked list where every node contains either 0 or 1 . These values together represent a binary number. The head of the list stores the most significant bit, meaning the binary digits appear in the same order that we normally write binary numbers from left to right. Our...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1332 - Remove Palindromic Subsequences

LeetCode Problem 1332 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem gives us a string s that contains only the characters 'a' and 'b' . In one operation, we are allowed to remove any subsequence of the string, as long as that subsequence forms a palindrome. A subsequence is different from a substring. A substring must be contiguous, but a subsequence can skip characters while preserving...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 709 - To Lower Case

LeetCode Problem 709 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to convert every uppercase English letter in a string into its lowercase equivalent. Any character that is already lowercase, or is not an alphabetic character at all, should remain unchanged. The input is a string s containing printable ASCII characters. Printable ASCII includes uppercase letters, lowercase letters, digits, punctuation, spaces, and symbols. The task is...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3053 - Classifying Triangles by Lengths

LeetCode Problem 3053 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires classifying triangles based on the lengths of their three sides, represented by the columns A , B , and C in the Triangles table. Each row in the table represents a potential triangle. The output should identify each triangle as one of four types: Equilateral , Isosceles , Scalene , or Not A Triangle . A...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 511 - Game Play Analysis I

LeetCode Problem 511 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to determine the first day each player logged into a game based on a table called Activity . Each row of this table contains a player_id , the device_id used, the event_date on which the player logged in, and the number of games_played during that session. The player_id and event_date combination is unique, so no...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1736 - Latest Time by Replacing Hidden Digits

LeetCode Problem 1736 Difficulty: 🟢 Easy Topics: String, Greedy Solution Problem Understanding The problem presents a string time formatted as hh:mm , where h and m are digits representing hours and minutes, respectively. Some digits may be hidden and are represented by a question mark ? . The goal is to replace the ? characters with digits such that the resulting time is the latest valid time possible , considering...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2027 - Minimum Moves to Convert String

LeetCode Problem 2027 Difficulty: 🟢 Easy Topics: String, Greedy Solution Problem Understanding The problem asks us to transform a string s containing only characters 'X' and 'O' so that all characters become 'O' . A move consists of selecting three consecutive characters and converting them to 'O' . If a character is already 'O' , it remains unchanged. The goal is to determine the minimum number of moves required to...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 867 - Transpose Matrix

LeetCode Problem 867 Difficulty: 🟢 Easy Topics: Array, Matrix, Simulation Solution LeetCode 867, Transpose Matrix Problem Understanding This problem asks us to compute the transpose of a given two dimensional matrix. A transpose operation flips a matrix across its main diagonal. In practical terms, every element at position (row, column) in the original matrix becomes the element at position (column, row) in the transposed matrix. If the input matrix has...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 182 - Duplicate Emails

LeetCode Problem 182 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Person with two columns: Column Description id A unique integer identifier for each row email The email address associated with that row The goal is to find all email addresses that appear more than once in the table. In other words, we need to identify duplicate email values. The output should...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 350 - Intersection of Two Arrays II

LeetCode Problem 350 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Binary Search, Sorting Solution Problem Understanding The problem asks us to find the intersection of two integer arrays, but with an important detail: duplicates matter. If a number appears multiple times in both arrays, it must appear in the result as many times as it appears in both. For example, if 2 appears twice in nums1 and three...

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LeetCode 1507 - Reformat Date

LeetCode Problem 1507 Difficulty: 🟢 Easy Topics: String Solution LeetCode 1507 - Reformat Date Problem Understanding The problem gives a date string in a human readable format such as "20th Oct 2052" and asks us to convert it into the standardized ISO style format YYYY-MM-DD . The input string always contains exactly three parts: A day value with an ordinal suffix such as "1st" , "2nd" , "3rd" , "4th"...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 697 - Degree of an Array

LeetCode Problem 697 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to find the shortest contiguous subarray of an array nums that has the same degree as the original array. The degree of an array is defined as the maximum frequency of any element in that array. In other words, if the element that appears the most appears k times, then k is the...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 724 - Find Pivot Index

LeetCode Problem 724 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution Problem Understanding The problem asks us to find an index in the array such that the sum of all elements strictly to the left of that index is equal to the sum of all elements strictly to the right of that index. More formally, for an index i : Left sum = nums[0] + nums[1] + ... + nums[i...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1748 - Sum of Unique Elements

LeetCode Problem 1748 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem gives us an integer array nums and asks us to compute the sum of all elements that appear exactly once in the array. An element is considered unique only if its frequency is exactly one. If a value appears two or more times, it must not contribute to the final sum at all. For...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1539 - Kth Missing Positive Number

LeetCode Problem 1539 Difficulty: 🟢 Easy Topics: Array, Binary Search Solution Problem Understanding The problem gives us a strictly increasing array of positive integers, arr , and an integer k . The array does not necessarily contain every positive integer. Some numbers are missing from the natural sequence starting at 1 . Our task is to determine the kth positive integer that does not appear in the array. For example,...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 66 - Plus One

LeetCode Problem 66 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem gives us a non-empty array of digits that together represent a large integer. Each element in the array is a single decimal digit, and the digits are stored in left-to-right order from the most significant digit to the least significant digit. For example: [1,2,3] represents the number 123 [4,3,2,1] represents the number 4321 [9] represents the...

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LeetCode 1566 - Detect Pattern of Length M Repeated K or More Times

LeetCode Problem 1566 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding The problem gives us an integer array arr and two integers, m and k . We need to determine whether there exists a contiguous subarray of length m that repeats consecutively at least k times. A pattern is considered valid only if: The repeated segments are consecutive Each repeated segment has exactly length m The repetitions do not...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1436 - Destination City

LeetCode Problem 1436 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding In this problem, we are given a list of directed paths between cities. Each entry in paths has the form [cityA, cityB] , which means there is a one way path from cityA to cityB . The graph formed by these paths is guaranteed to represent a straight travel chain with no cycles. This guarantee is...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 637 - Average of Levels in Binary Tree

LeetCode Problem 637 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding In this problem, we are given the root node of a binary tree, and we need to compute the average value of all nodes at each depth level of the tree. A binary tree is organized into levels. The root node is at level 0 , its children are at level 1 ,...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1374 - Generate a String With Characters That Have Odd Counts

LeetCode Problem 1374 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to generate a string of length n such that each character in the string occurs an odd number of times . The string must consist only of lowercase English letters. The input n is a positive integer ranging from 1 to 500, so the algorithm needs to handle small and moderately large strings efficiently. The...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1322 - Ads Performance

LeetCode Problem 1322 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the Click-Through Rate, abbreviated as CTR, for every advertisement stored in the Ads table. The table contains three columns: Column Meaning ad_id Identifier of the advertisement user_id Identifier of the user interacting with the ad action The interaction type, either Clicked , Viewed , or Ignored The CTR formula is: $$CTR = \frac{\text{number...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 999 - Available Captures for Rook

LeetCode Problem 999 Difficulty: 🟢 Easy Topics: Array, Matrix, Simulation Solution Problem Understanding The problem gives us an 8 x 8 chessboard represented as a matrix of characters. Each cell contains one of four possible values: 'R' represents the white rook 'p' represents a black pawn 'B' represents a white bishop '.' represents an empty square There is exactly one rook on the board. The task is to determine how...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1360 - Number of Days Between Two Dates

LeetCode Problem 1360 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem gives two dates in the format YYYY-MM-DD and asks us to compute the absolute number of days between them. Each input string represents a valid calendar date. The year, month, and day are separated by hyphens. For example: "2019-06-29" means June 29, 2019 "2020-01-15" means January 15, 2020 The expected output is a single integer representing...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 993 - Cousins in Binary Tree

LeetCode Problem 993 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether two nodes in a binary tree are cousins. Two nodes are considered cousins if they satisfy two conditions simultaneously: They are located at the same depth in the tree. They have different parents. The input consists of: root , which is the root node of a...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 496 - Next Greater Element I

LeetCode Problem 496 Difficulty: 🟢 Easy Topics: Array, Hash Table, Stack, Monotonic Stack Solution Problem Understanding The problem is asking us to find the next greater element for each element in nums1 within another array nums2 . Formally, for each element in nums1 , we need to locate its position in nums2 and then find the first element to its right in nums2 that is greater than itself . If...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1128 - Number of Equivalent Domino Pairs

LeetCode Problem 1128 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding The problem is asking us to count all pairs of dominoes in a list that are equivalent, where two dominoes [a, b] and [c, d] are considered equivalent if one is a rotation of the other, meaning either (a == c and b == d) or (a == d and b == c) . In other...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 953 - Verifying an Alien Dictionary

LeetCode Problem 953 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding This problem asks us to verify whether a list of words is sorted according to a custom alphabet order, instead of the normal English alphabetical order. In normal lexicographical ordering, characters are compared from left to right using the standard alphabet. Here, the alien language still uses lowercase English letters, but the relative order of those...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 596 - Classes With at Least 5 Students

LeetCode Problem 596 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem is asking us to find classes in a school database that have at least five students enrolled. The input is a table named Courses with two columns: student and class . Each row represents one student being enrolled in one class. The primary key of this table is the combination of (student, class) , so there are...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1118 - Number of Days in a Month

LeetCode Problem 1118 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine the number of days in a specific month of a given year. The inputs are two integers: year , which ranges from 1583 to 2100, and month , which ranges from 1 (January) to 12 (December). The output is a single integer representing the total number of days in that month for that...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1677 - Product's Worth Over Invoices

LeetCode Problem 1677 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to calculate aggregate monetary information for each product based on invoices. We have two tables: Product and Invoice . The Product table contains a unique product_id and the name of the product. The Invoice table contains individual invoices for products, including amounts for rest (amount left to pay), paid , canceled , and refunded ....

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1741 - Find Total Time Spent by Each Employee

LeetCode Problem 1741 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to calculate the total time each employee spends in the office per day based on a table of their in and out times. Each row in the Employees table represents a single period that an employee was in the office, with columns for emp_id , event_day , in_time , and out_time . The in_time and...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 512 - Game Play Analysis II

LeetCode Problem 512 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Activity . Each row represents one login session for a player on a specific date. The table contains four columns: Column Meaning player_id The unique identifier for a player device_id The device used during that login session event_date The date of the login games_played Number of games played during that session The...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 141 - Linked List Cycle

LeetCode Problem 141 Difficulty: 🟢 Easy Topics: Hash Table, Linked List, Two Pointers Solution LeetCode 141, Linked List Cycle Problem Understanding This problem asks us to determine whether a singly linked list contains a cycle. A cycle exists when following the next pointers eventually leads back to a node that has already been visited, instead of reaching None . The input is the head node of a singly linked list....

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1337 - The K Weakest Rows in a Matrix

LeetCode Problem 1337 Difficulty: 🟢 Easy Topics: Array, Binary Search, Sorting, Heap (Priority Queue), Matrix Solution Here is a comprehensive, detailed solution guide for LeetCode 1337 following your exact instructions. Problem Understanding The problem provides a binary m x n matrix mat , where each element is either 1 (representing a soldier) or 0 (representing a civilian). In each row, soldiers are always positioned before civilians, meaning all 1 s...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 976 - Largest Perimeter Triangle

LeetCode Problem 976 Difficulty: 🟢 Easy Topics: Array, Math, Greedy, Sorting Solution Problem Understanding The problem gives us an array of integers called nums , where each integer represents a possible side length. Our goal is to select exactly three lengths that can form a valid triangle with a non-zero area, and among all valid triangles, return the maximum possible perimeter. A triangle is only valid if the sum of...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1486 - XOR Operation in an Array

LeetCode Problem 1486 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation Solution Problem Understanding The problem gives us two integers, n and start . We must construct an array named nums of length n , where each element is defined by the formula: $$nums[i] = start + 2 \times i$$ This means the array begins at start and increases by 2 for every next position. After constructing the array, we must...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1176 - Diet Plan Performance

LeetCode Problem 1176 Difficulty: 🟢 Easy Topics: Array, Sliding Window Solution Problem Understanding The problem is asking us to simulate a dieter’s performance over a sequence of days based on their calorie consumption. The input is an array calories where calories[i] represents the number of calories consumed on day i . We are also given three integers: k , lower , and upper . For every consecutive sequence of k...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 67 - Add Binary

LeetCode Problem 67 Difficulty: 🟢 Easy Topics: Math, String, Bit Manipulation, Simulation Solution LeetCode 67, Add Binary Problem Statement You are given two strings, a and b , where each string represents a binary number. A binary number contains only the characters '0' and '1' . The task is to add these two binary numbers together and return the result as another binary string. Unlike normal decimal addition, binary addition...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 599 - Minimum Index Sum of Two Lists

LeetCode Problem 599 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding This problem is asking us to find the common elements between two lists of strings, but not just any common elements. We want the ones where the sum of their indices in both lists is the smallest. In other words, if a string appears at index i in list1 and index j in list2 , we...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1002 - Find Common Characters

LeetCode Problem 1002 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding The problem gives us an array of lowercase strings called words . We must return all characters that appear in every string in the array, including duplicate occurrences. The important detail is that duplicates matter. If a character appears multiple times in every word, then it must appear multiple times in the answer as well. For...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 292 - Nim Game

LeetCode Problem 292 Difficulty: 🟢 Easy Topics: Math, Brainteaser, Game Theory Solution Problem Understanding The problem describes a two-player game involving a single heap of stones. There are n stones initially on the table, and players alternate turns removing stones. On each turn, a player may remove either 1, 2, or 3 stones. The player who removes the final stone wins the game. You always move first, and both players...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 892 - Surface Area of 3D Shapes

LeetCode Problem 892 Difficulty: 🟢 Easy Topics: Array, Math, Geometry, Matrix Solution Problem Understanding The problem gives us an n x n matrix called grid , where each cell contains a non-negative integer. The value grid[i][j] represents how many 1 x 1 x 1 cubes are stacked vertically at position (i, j) . Each cube contributes surface area through its exposed faces. A single cube has 6 faces, but when...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1403 - Minimum Subsequence in Non-Increasing Order

LeetCode Problem 1403 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution Problem Understanding The problem gives an integer array nums and asks us to build a subsequence whose sum is strictly greater than the sum of all elements that are not included in the subsequence. A subsequence means we are allowed to remove elements from the array while preserving the remaining elements. However, the final answer must be returned in...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1661 - Average Time of Process per Machine

LeetCode Problem 1661 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Activity , which stores information about processes executed on different machines. Each process has exactly two records: A "start" record, indicating when the process began An "end" record, indicating when the process finished Each row contains four columns: Column Meaning machine_id The machine executing the process process_id The specific process running on...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1484 - Group Sold Products By The Date

LeetCode Problem 1484 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Activities with two columns: Column Meaning sell_date The date a product was sold product The name of the product The table does not contain a primary key, which means duplicate rows may exist. For example, the same product could appear multiple times on the same date. We need to generate a...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1065 - Index Pairs of a String

LeetCode Problem 1065 Difficulty: 🟢 Easy Topics: Array, String, Trie, Sorting Solution Problem Understanding The problem gives us a string called text and a list of dictionary words called words . We must find every substring inside text that exactly matches one of the words in the dictionary. For every valid match, we return the pair [i, j] , where: i is the starting index of the substring j is...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 231 - Power of Two

LeetCode Problem 231 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation, Recursion Solution Problem Understanding The problem asks us to determine whether a given integer n is a power of two. A number is considered a power of two if it can be written in the form: $$n = 2^x$$ where x is a non-negative integer. Some examples of powers of two are: 1 = 2^0 2 = 2^1 4 =...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1684 - Count the Number of Consistent Strings

LeetCode Problem 1684 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Bit Manipulation, Counting Solution Problem Understanding This problem asks us to determine how many strings in the words array are consistent with a given set of allowed characters. You are given two inputs: allowed , a string containing distinct lowercase English letters. words , an array of lowercase strings. A word is considered consistent if every character in that...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1480 - Running Sum of 1d Array

LeetCode Problem 1480 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution LeetCode 1480 - Running Sum of 1d Array Problem Understanding The problem asks us to compute the running sum, also called the prefix sum, of a one dimensional integer array. For every index i , the result at position i should equal the sum of all elements from index 0 through index i in the original array. In other...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1619 - Mean of Array After Removing Some Elements

LeetCode Problem 1619 Difficulty: 🟢 Easy Topics: Array, Sorting Solution LeetCode 1619, Mean of Array After Removing Some Elements Problem Understanding The problem gives us an integer array arr and asks us to compute the average value after removing the smallest 5% and the largest 5% of the elements. The important detail is that the removal is based on the sorted order of the array. We are not simply removing...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 696 - Count Binary Substrings

LeetCode Problem 696 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem gives us a binary string, meaning the string contains only the characters '0' and '1' . We need to count how many substrings satisfy two conditions simultaneously: The substring contains the same number of 0 s and 1 s. All 0 s are grouped together and all 1 s are grouped together. The second condition...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 170 - Two Sum III - Data structure design

LeetCode Problem 170 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Design, Data Stream Solution Problem Understanding The problem asks us to design a data structure that supports two operations efficiently over a stream of integers. The first operation, add(number) , inserts a number into the data structure. Numbers may appear multiple times, so duplicates must be handled correctly. The second operation, find(value) , checks whether there exists any...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1089 - Duplicate Zeros

LeetCode Problem 1089 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding The problem asks us to modify a fixed-length integer array in-place by duplicating each zero and shifting the subsequent elements to the right. The critical part of the problem is that the array has a fixed length, so any elements that would go beyond the original size are discarded. For example, if duplicating a zero would push...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2016 - Maximum Difference Between Increasing Elements

LeetCode Problem 2016 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem is asking us to find the maximum difference between two elements in an array, with the condition that the smaller element appears before the larger element. Formally, given a 0-indexed array nums of length n , we need to find the largest value of nums[j] - nums[i] where i < j and nums[i] < nums[j] . If...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 703 - Kth Largest Element in a Stream

LeetCode Problem 703 Difficulty: 🟢 Easy Topics: Tree, Design, Binary Search Tree, Heap (Priority Queue), Binary Tree, Data Stream Solution Problem Understanding The problem asks us to design a data structure that continuously tracks the kth largest element in a stream of integers. We are given an integer k and an initial list of numbers called nums . After initialization, new numbers are added one at a time using the...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 145 - Binary Tree Postorder Traversal

LeetCode Problem 145 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to return the postorder traversal of a binary tree. A binary tree is made of nodes, where each node contains: A value A pointer to a left child A pointer to a right child In postorder traversal, we must visit nodes in this exact order: Traverse the left subtree Traverse...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1790 - Check if One String Swap Can Make Strings Equal

LeetCode Problem 1790 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks us to determine if two strings of equal length, s1 and s2 , can be made identical by performing at most one string swap on exactly one of the strings . A string swap allows exchanging any two characters at different or same indices. The task is not to perform multiple swaps or...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 228 - Summary Ranges

LeetCode Problem 228 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 228, Summary Ranges Problem Understanding The problem gives us a sorted array of unique integers and asks us to summarize consecutive values into compact range strings. A range represents a continuous sequence of integers. For example, the numbers [4,5,6] can be represented as "4->6" because every integer between 4 and 6 exists in the array. A single isolated value such...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1512 - Number of Good Pairs

LeetCode Problem 1512 Difficulty: 🟢 Easy Topics: Array, Hash Table, Math, Counting Solution LeetCode 1512 - Number of Good Pairs Problem Understanding The problem gives us an integer array nums and asks us to count how many pairs of indices (i, j) satisfy two conditions: nums[i] == nums[j] i < j Such pairs are called "good pairs". In simpler terms, we need to count how many times the same value...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 501 - Find Mode in Binary Search Tree

LeetCode Problem 501 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to find the mode(s) in a Binary Search Tree (BST). A mode is the value that appears most frequently in the tree. Since duplicates are allowed in this BST definition, a value may occur multiple times. The input is the root node of a BST. Every node contains...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1086 - High Five

LeetCode Problem 1086 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Heap (Priority Queue) Solution Problem Understanding The problem asks us to compute the top five average score for each student given a list of [ID, score] pairs. Each ID represents a unique student, and score represents a single score they received. The goal is to return a list of [ID, topFiveAverage] pairs, where topFiveAverage is calculated by taking the...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 530 - Minimum Absolute Difference in BST

LeetCode Problem 530 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root node of a Binary Search Tree, abbreviated as BST, and asks us to find the minimum absolute difference between the values of any two distinct nodes in the tree. A Binary Search Tree has a very important property: Every value in the left subtree...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 383 - Ransom Note

LeetCode Problem 383 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding This problem asks whether it is possible to construct the string ransomNote using characters taken from the string magazine . Each character in magazine can only be used once, which means character frequency matters. If ransomNote requires more occurrences of a letter than magazine contains, the answer must be false . In other words, we need...

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LeetCode 541 - Reverse String II

LeetCode Problem 541 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem requires us to manipulate a string s in a structured way. Specifically, we need to reverse the first k characters for every consecutive block of 2k characters in the string. If a block has fewer than k characters, we reverse all of them. If a block has between k and 2k characters, we reverse the...

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LeetCode 1078 - Occurrences After Bigram

LeetCode Problem 1078 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string called text and two target words, first and second . We must find every occurrence where the words appear consecutively in the exact order: first second third For every such occurrence, we return the value of third . The important detail is that the words must appear immediately next to each other in...

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LeetCode 832 - Flipping an Image

LeetCode Problem 832 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Bit Manipulation, Matrix, Simulation Solution Problem Understanding The problem requires transforming an n x n binary matrix in two steps: first flipping it horizontally, then inverting it. Horizontally flipping a row means reversing the order of elements in that row, so the first element becomes last, the second becomes second-to-last, and so on. Inverting a row means changing all 0...

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LeetCode 812 - Largest Triangle Area

LeetCode Problem 812 Difficulty: 🟢 Easy Topics: Array, Math, Geometry Solution LeetCode 812, Largest Triangle Area Problem Understanding The problem gives us a list of unique points on a 2D X-Y plane. Each point is represented as a pair of integers [x, y] . Our task is to choose any three distinct points and compute the area of the triangle formed by those points. Among all possible triangles, we must...

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LeetCode 760 - Find Anagram Mappings

LeetCode Problem 760 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to build an index mapping from nums1 to nums2 , where nums2 is guaranteed to be an anagram of nums1 . Since an anagram means the same elements appear in both arrays, but possibly in a different order, every value in nums1 must appear somewhere in nums2 . For each element nums1[i] ,...

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LeetCode 1491 - Average Salary Excluding the Minimum and Maximum Salary

LeetCode Problem 1491 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem gives us an array called salary , where each element represents the salary of an employee. Every salary value is unique, meaning no two employees have the same salary. Our task is to compute the average salary after excluding exactly one minimum salary and one maximum salary from the array. In other words, we must: Find...

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LeetCode 1789 - Primary Department for Each Employee

LeetCode Problem 1789 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Employee that stores information about which departments employees belong to. Each row contains three values: Column Meaning employee_id The employee identifier department_id A department the employee belongs to primary_flag Whether this department is the employee's primary department The combination (employee_id, department_id) is unique, meaning the same employee cannot appear twice for the...

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LeetCode 1474 - Delete N Nodes After M Nodes of a Linked List

LeetCode Problem 1474 Difficulty: 🟢 Easy Topics: Linked List Solution LeetCode 1474, Delete N Nodes After M Nodes of a Linked List Problem Understanding This problem gives us the head of a singly linked list and two integers, m and n . We must traverse the linked list while repeatedly applying a fixed pattern: Keep the next m nodes. Delete the following n nodes. Continue repeating this process until the...

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LeetCode 222 - Count Complete Tree Nodes

LeetCode Problem 222 Difficulty: 🟢 Easy Topics: Binary Search, Bit Manipulation, Tree, Binary Tree Solution Problem Understanding The problem asks us to count how many nodes exist in a complete binary tree. A complete binary tree has a very specific structure. Every level except possibly the last one is completely filled, and the nodes on the final level appear as far left as possible. The input is the root node...

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LeetCode 1710 - Maximum Units on a Truck

LeetCode Problem 1710 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution LeetCode 1710 - Maximum Units on a Truck Problem Understanding The problem gives us several types of boxes, where each box type contains two values: The number of boxes available for that type The number of units inside each box of that type We also have a truck that can carry at most truckSize boxes total, regardless of type....

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LeetCode 1777 - Product's Price for Each Store

LeetCode Problem 1777 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a table named Products , where each row represents the price of a specific product in a specific store. Every row contains three values: product_id , identifying the product store , identifying which store sells the product price , representing the price of that product in that store The (product_id, store) pair is guaranteed to be...

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LeetCode 441 - Arranging Coins

LeetCode Problem 441 Difficulty: 🟢 Easy Topics: Math, Binary Search Solution Problem Understanding The problem asks us to determine how many complete rows of a coin staircase can be formed using exactly n coins. A staircase arrangement follows a very specific structure: The first row contains 1 coin The second row contains 2 coins The third row contains 3 coins Continuing in this pattern, the kth row contains exactly k...

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LeetCode 1426 - Counting Elements

LeetCode Problem 1426 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to count the number of elements in an array arr for which the value plus one also exists in the array. In other words, for every element x in the array, we check whether x + 1 is also present. If it is, we include x in our count. If duplicates exist, each...

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LeetCode 804 - Unique Morse Code Words

LeetCode Problem 804 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding The problem asks us to determine how many unique Morse code transformations exist among a list of words. Each lowercase English letter maps to a specific Morse code representation. A word can be transformed into Morse code by replacing each character with its Morse equivalent and concatenating the results together into a single string. For example,...

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LeetCode 1085 - Sum of Digits in the Minimum Number

LeetCode Problem 1085 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding This problem asks us to examine the smallest number in the input array and determine whether the sum of its digits is odd or even. We are given an integer array nums . The task consists of three clear steps: Find the minimum integer in the array. Compute the sum of its digits . Return: 1 if the...

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LeetCode 766 - Toeplitz Matrix

LeetCode Problem 766 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem asks us to determine whether a given matrix satisfies the Toeplitz property. A matrix is considered Toeplitz if every diagonal running from the top-left corner toward the bottom-right corner contains identical values. More formally, for every valid position (row, col) in the matrix, the value at that position must match the value diagonally down and to...

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LeetCode 1470 - Shuffle the Array

LeetCode Problem 1470 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 1470 - Shuffle the Array Problem Understanding The problem gives us an array nums with exactly 2n elements. The structure of the array is guaranteed to follow a very specific pattern: [x1, x2, ..., xn, y1, y2, ..., yn] This means the first half of the array contains all the x values, and the second half contains all the y...

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LeetCode 1047 - Remove All Adjacent Duplicates In String

LeetCode Problem 1047 Difficulty: 🟢 Easy Topics: String, Stack Solution Problem Understanding The problem gives us a string s containing only lowercase English letters. We repeatedly look for two adjacent characters that are equal, remove both of them, and continue this process until no such adjacent duplicate pair exists. The important detail is that removals can create new adjacent duplicates that were not adjacent before. For example, in the string...

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LeetCode 242 - Valid Anagram

LeetCode Problem 242 Difficulty: 🟢 Easy Topics: Hash Table, String, Sorting Solution Problem Understanding The problem asks us to determine whether two strings are anagrams of each other. Two strings are considered anagrams if they contain exactly the same characters with exactly the same frequencies , but possibly in a different order. In other words, one string can be rearranged to form the other. For example, "anagram" and "nagaram" are...

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LeetCode 933 - Number of Recent Calls

LeetCode Problem 933 Difficulty: 🟢 Easy Topics: Design, Queue, Data Stream Solution Problem Understanding The problem asks us to implement a class RecentCounter that tracks the number of requests (or pings) made in the last 3000 milliseconds. Every time the ping(t) method is called with a time t , we are asked to return how many requests occurred within the time interval [t - 3000, t] . The class starts...

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LeetCode 58 - Length of Last Word

LeetCode Problem 58 Difficulty: 🟢 Easy Topics: String Solution LeetCode 58, Length of Last Word Problem Understanding The problem gives us a string s that contains English letters and spaces. Inside this string, words are separated by spaces, and there may also be extra spaces at the beginning or end of the string. Our task is to return the length of the last word in the string. A word is...

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LeetCode 293 - Flip Game

LeetCode Problem 293 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem is asking us to simulate a single move in a simple two-player game. The input is a string currentState consisting only of '+' and '-' characters. Each '+' represents a spot that can be flipped, and the rules allow a player to flip two consecutive '+' characters into '--' . The task is to generate all possible...

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LeetCode 2032 - Two Out of Three

LeetCode Problem 2032 Difficulty: 🟢 Easy Topics: Array, Hash Table, Bit Manipulation Solution Problem Understanding The problem asks us to identify all distinct integers that appear in at least two out of three given integer arrays . The input consists of three arrays nums1 , nums2 , and nums3 , each containing integers in the range [1, 100] . The output is an array of integers that occur in at...

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LeetCode 1511 - Customer Order Frequency

LeetCode Problem 1511 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify customers who consistently spend at least $100 in each of two consecutive months, June and July of 2020. We have three tables: Customers , which lists customer details; Product , which lists products and their prices; and Orders , which logs all purchases by customers with the quantity and date. The input represents...

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LeetCode 925 - Long Pressed Name

LeetCode Problem 925 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding In this problem, we are given two strings, name and typed . The string name represents the intended sequence of characters your friend wanted to type. The string typed represents the actual characters that appeared on the screen. The complication is that some keys may have been long pressed. A long press means that when a character...

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LeetCode 101 - Symmetric Tree

LeetCode Problem 101 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether a binary tree is symmetric around its center. A tree is symmetric if the left subtree is a mirror reflection of the right subtree. In a mirror relationship, the following conditions must hold: The values of the corresponding nodes must be equal. The left child of...

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LeetCode 1294 - Weather Type in Each Country

LeetCode Problem 1294 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to determine the weather type for each country during November 2019 , based on the average weather_state recorded in that month. We are given two database tables: The Countries table stores information about countries. Each row contains a unique country_id and its corresponding country_name . The Weather table stores daily weather information for countries. Each...

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LeetCode 28 - Find the Index of the First Occurrence in a String

LeetCode Problem 28 Difficulty: 🟢 Easy Topics: Two Pointers, String, String Matching Solution Problem Understanding This problem asks us to locate the first occurrence of one string inside another string. The string we are searching for is called needle , and the larger string we search inside is called haystack . More formally, we need to determine whether needle appears as a contiguous substring inside haystack . If it does,...

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LeetCode 345 - Reverse Vowels of a String

LeetCode Problem 345 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem asks us to reverse only the vowels in a string while leaving all non-vowel characters in their original positions. A vowel is defined as one of the following characters: a e i o u The problem also states that vowels may appear in both lowercase and uppercase forms. This means characters like A , E...

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LeetCode 819 - Most Common Word

LeetCode Problem 819 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Counting Solution Problem Understanding The problem asks us to process a paragraph of text and determine which word appears most frequently, while ignoring a given list of banned words. The final answer must be returned in lowercase. Several important details make this problem slightly more involved than simple word counting. First, the paragraph may contain punctuation such as commas,...

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LeetCode 169 - Majority Element

LeetCode Problem 169 Difficulty: 🟢 Easy Topics: Array, Hash Table, Divide and Conquer, Sorting, Counting Solution Problem Understanding The problem asks us to identify the majority element in a given array of integers nums . The majority element is defined as the number that appears more than half of the times in the array, i.e., more than ⌊n / 2⌋ times where n is the length of the array. The...

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LeetCode 1495 - Friendly Movies Streamed Last Month

LeetCode Problem 1495 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to find the titles of movies that satisfy three separate conditions at the same time. First, the content must be marked as kid-friendly. In the Content table, this is represented by the column Kids_content = 'Y' . Second, the content must actually be a movie. The content_type column tells us whether a piece of content...

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LeetCode 108 - Convert Sorted Array to Binary Search Tree

LeetCode Problem 108 Difficulty: 🟢 Easy Topics: Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us a sorted integer array nums in strictly increasing order and asks us to convert it into a height-balanced binary search tree (BST) . A binary search tree is a binary tree where: Every node in the left subtree contains values smaller than the current node. Every...

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LeetCode 1200 - Minimum Absolute Difference

LeetCode Problem 1200 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem asks us to find all pairs of numbers in an array that have the smallest absolute difference. In other words, given a list of distinct integers, we want to identify every pair [a, b] such that the difference b - a is minimized across all possible pairs in the array, and we always list the smaller...

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LeetCode 1556 - Thousand Separator

LeetCode Problem 1556 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to format a non-negative integer so that every group of three digits is separated by a dot ( . ), starting from the right side of the number. For example, the number 1234567 should become "1.234.567" because the digits are grouped as: 1 234 567 The input is a single integer n , and the...

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LeetCode 1455 - Check If a Word Occurs As a Prefix of Any Word in a Sentence

LeetCode Problem 1455 Difficulty: 🟢 Easy Topics: Two Pointers, String, String Matching Solution Problem Understanding The problem asks us to determine whether a given searchWord occurs as a prefix of any word within a sentence. A sentence is defined as a string of lowercase English letters separated by single spaces, and a prefix is any contiguous leading substring of a word. We are asked to return the 1-indexed position of...

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LeetCode 619 - Biggest Single Number

LeetCode Problem 619 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named MyNumbers that contains a single column, num . The table may contain duplicate values because there is no primary key restriction. Our task is to find the largest number that appears exactly once in the table. A number is considered a "single number" if its frequency in the table is exactly...

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LeetCode 1603 - Design Parking System

LeetCode Problem 1603 Difficulty: 🟢 Easy Topics: Design, Simulation, Counting Solution Problem Understanding This problem asks us to design a very small parking lot management system. The parking lot contains exactly three types of parking spaces: Big parking spaces Medium parking spaces Small parking spaces The constructor receives the number of available spaces for each type. After initialization, cars arrive one at a time, and for every arriving car we...

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LeetCode 746 - Min Cost Climbing Stairs

LeetCode Problem 746 Difficulty: 🟢 Easy Topics: Array, Dynamic Programming Solution LeetCode 746 - Min Cost Climbing Stairs Problem Understanding This problem gives us an array named cost , where each element represents the cost of stepping onto a particular stair. If cost[i] equals 10 , that means stepping on stair i requires paying 10 . From any stair, we are allowed to move either one step or two steps...

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LeetCode 1280 - Students and Examinations

LeetCode Problem 1280 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to generate a complete report showing how many times every student attended every subject examination. We are given three database tables: Students , which stores each student's ID and name. Subjects , which stores every subject offered in the school. Examinations , which records every exam attendance entry. The important detail is that the Examinations...

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LeetCode 1422 - Maximum Score After Splitting a String

LeetCode Problem 1422 Difficulty: 🟢 Easy Topics: String, Prefix Sum Solution Problem Understanding The problem gives us a binary string s , meaning the string contains only the characters '0' and '1' . We must split this string into two non-empty parts, a left substring and a right substring. For every possible split position, we calculate a score defined as: the number of '0' characters in the left substring plus...

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LeetCode 1464 - Maximum Product of Two Elements in an Array

LeetCode Problem 1464 Difficulty: 🟢 Easy Topics: Array, Sorting, Heap (Priority Queue) Solution Problem Understanding The problem gives an integer array nums , and asks us to choose two different indices i and j . For those two elements, we compute the expression: $(nums[i]-1)(nums[j]-1)$ Our goal is to return the maximum possible value of this expression. In simpler terms, we need to find the two numbers in the array that...

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LeetCode 359 - Logger Rate Limiter

LeetCode Problem 359 Difficulty: 🟢 Easy Topics: Hash Table, Design, Data Stream Solution Problem Understanding The problem asks us to design a logging system that controls how frequently identical messages can be printed. Each message is associated with a timestamp, and the same message is only allowed to be printed once every 10 seconds. More specifically, when a message is printed at timestamp t , the next time the exact...

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LeetCode 1576 - Replace All ?'s to Avoid Consecutive Repeating Characters

LeetCode Problem 1576 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to take a string s consisting of lowercase English letters and the character '?' and replace every '?' with a lowercase letter so that no two consecutive characters in the resulting string are the same . Importantly, we are not allowed to change any existing letters in the string. The input string can be of...

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LeetCode 594 - Longest Harmonious Subsequence

LeetCode Problem 594 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sliding Window, Sorting, Counting Solution Problem Understanding The problem asks us to find the length of the longest harmonious subsequence in an integer array. A harmonious array is defined as one where the difference between the maximum and minimum values is exactly 1 . In simpler terms, given an array nums , we are searching for the longest collection of...

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LeetCode 232 - Implement Queue using Stacks

LeetCode Problem 232 Difficulty: 🟢 Easy Topics: Stack, Design, Queue Solution Problem Understanding The problem asks us to implement a queue using only stack operations. A queue follows the FIFO, First In First Out, principle. The first element inserted into the queue must be the first element removed. In contrast, a stack follows the LIFO, Last In First Out, principle, where the most recently inserted element is removed first. We...

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LeetCode 2231 - Largest Number After Digit Swaps by Parity

LeetCode Problem 2231 Difficulty: 🟢 Easy Topics: Sorting, Heap (Priority Queue) Solution Problem Understanding The problem gives us a positive integer num and allows us to swap digits only if the two digits have the same parity. In other words, an odd digit can only be swapped with another odd digit, and an even digit can only be swapped with another even digit. The goal is to return the largest...

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LeetCode 157 - Read N Characters Given Read4

LeetCode Problem 157 Difficulty: 🟢 Easy Topics: Array, Simulation, Interactive Solution Problem Understanding This problem asks us to implement a read function using a restricted API called read4 . The file itself is hidden from us, and the only way to access its contents is by repeatedly calling read4 . The read4 API reads up to 4 consecutive characters from the file into a temporary buffer called buf4 . It...

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LeetCode 1693 - Daily Leads and Partners

LeetCode Problem 1693 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named DailySales , where each row represents a sale event involving a product manufacturer ( make_name ), a lead ( lead_id ), and a partner ( partner_id ) on a specific date ( date_id ). The goal is to compute, for every unique combination of date_id and make_name , two values: The number...

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LeetCode 1082 - Sales Analysis I

LeetCode Problem 1082 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify the seller or sellers who generated the highest total sales revenue. We are given two database tables: Product and Sales . The Product table contains information about products, including their IDs, names, and unit prices. The Sales table records transactions, where each row represents a sale and includes details such as the seller...

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LeetCode 104 - Maximum Depth of Binary Tree

LeetCode Problem 104 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine the maximum depth of a binary tree. A binary tree consists of nodes where each node can have up to two children, a left child and a right child. The depth of a tree is defined as the number of nodes along the longest path from the...

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LeetCode 1636 - Sort Array by Increasing Frequency

LeetCode Problem 1636 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem asks us to reorder an array of integers based on the frequency of each value. Specifically, elements with lower frequency should appear before elements with higher frequency. If two elements have the same frequency, the one with the larger value should appear first. In other words, the sort is primary by increasing frequency and...

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LeetCode 509 - Fibonacci Number

LeetCode Problem 509 Difficulty: 🟢 Easy Topics: Math, Dynamic Programming, Recursion, Memoization Solution Problem Understanding This problem asks us to compute the n th Fibonacci number. The Fibonacci sequence is defined recursively. The first two numbers are fixed: F(0) = 0 F(1) = 1 Every value after that is calculated as the sum of the previous two values: F(n) = F(n - 1) + F(n - 2) Given an integer...

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LeetCode 500 - Keyboard Row

LeetCode Problem 500 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding This problem asks us to determine which words in a given list can be typed using letters from only one row of an American keyboard. The input is an array of strings, words , where each string represents a word consisting only of English alphabet characters. The task is to return only those words where every...

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LeetCode 88 - Merge Sorted Array

LeetCode Problem 88 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Sorting Solution LeetCode 88 - Merge Sorted Array Problem Understanding This problem gives us two arrays, nums1 and nums2 , where both arrays are already sorted in non-decreasing order. We are also given two integers, m and n , which tell us how many valid elements exist in each array. The important detail is that nums1 has extra space at...

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LeetCode 1407 - Top Travellers

LeetCode Problem 1407 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 1407 - Top Travellers Problem Understanding This problem gives us two database tables, Users and Rides . The Users table contains information about each user. Every user has a unique id and a corresponding name . The Rides table contains ride records. Each ride has its own unique id , a user_id indicating which user took the ride, and a...

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LeetCode 771 - Jewels and Stones

LeetCode Problem 771 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding In this problem, we are given two strings, jewels and stones . The string jewels represents all stone types that are considered jewels. Each character is a unique jewel type. For example, if jewels = "aA" , then both lowercase 'a' and uppercase 'A' are jewel types. The string stones represents all stones we currently own. Every...

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LeetCode 1030 - Matrix Cells in Distance Order

LeetCode Problem 1030 Difficulty: 🟢 Easy Topics: Array, Math, Geometry, Sorting, Matrix Solution Problem Understanding This problem asks us to return every cell in a matrix, ordered by its Manhattan distance from a given center cell. We are given four integers: rows , the number of rows in the matrix cols , the number of columns in the matrix rCenter , the row index of the reference cell cCenter ,...

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LeetCode 1241 - Number of Comments per Post

LeetCode Problem 1241 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to analyze a database table named Submissions and determine how many unique comments belong to each post. The table contains two columns: Column Meaning sub_id The ID of the current submission parent_id The parent submission ID A row represents either a post or a comment: If parent_id is NULL , the row is a post....

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LeetCode 1037 - Valid Boomerang

LeetCode Problem 1037 Difficulty: 🟢 Easy Topics: Array, Math, Geometry Solution Problem Understanding This problem asks us to determine whether three given points in a 2D Cartesian plane form a valid boomerang. A boomerang is defined as a set of three points that are all distinct and not in a straight line . In other words, the points must not coincide and must not be collinear. The input is always...

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LeetCode 1614 - Maximum Nesting Depth of the Parentheses

LeetCode Problem 1614 Difficulty: 🟢 Easy Topics: String, Stack Solution LeetCode 1614, Maximum Nesting Depth of the Parentheses Problem Understanding This problem asks us to compute the maximum nesting depth of parentheses in a valid parentheses string. A valid parentheses string, often abbreviated as VPS, is a string where every opening parenthesis '(' has a matching closing parenthesis ')' , and the parentheses are properly balanced. The string may also...

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LeetCode 1025 - Divisor Game

LeetCode Problem 1025 Difficulty: 🟢 Easy Topics: Math, Dynamic Programming, Brainteaser, Game Theory Solution Problem Understanding The problem describes a two-player turn-based game between Alice and Bob. The game starts with a single integer n written on a chalkboard. Alice always takes the first turn. On each turn, the current player must choose a positive integer x such that: 0 < x < n x divides n evenly, meaning n...

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LeetCode 1046 - Last Stone Weight

LeetCode Problem 1046 Difficulty: 🟢 Easy Topics: Array, Heap (Priority Queue) Solution Problem Understanding This problem asks us to repeatedly simulate a process involving stones with different weights. At every turn, we must select the two heaviest stones , smash them together, and update the collection based on the result. If the two heaviest stones have the same weight, both are destroyed and disappear from the collection. If the stones...

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LeetCode 1379 - Find a Corresponding Node of a Binary Tree in a Clone of That Tree

LeetCode Problem 1379 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The traversal is by reference, not value.

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LeetCode 1624 - Largest Substring Between Two Equal Characters

LeetCode Problem 1624 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks us to find the length of the longest substring that lies between two identical characters in a given string s . The substring does not include the two identical characters themselves. If no character occurs at least twice, we must return -1 . In other words, we are looking for pairs of identical characters...

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LeetCode 584 - Find Customer Referee

LeetCode Problem 584 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a Customer table with three columns: id , name , and referee_id . Each row represents a customer, their unique identifier ( id ), their name, and optionally the id of the customer who referred them. A null value in referee_id indicates that the customer was not referred by anyone. The task is to identify all...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 459 - Repeated Substring Pattern

LeetCode Problem 459 Difficulty: 🟢 Easy Topics: String, String Matching Solution Problem Understanding The problem asks us to determine whether a given string can be formed by repeating one of its substrings multiple times. In other words, we want to know if there exists some substring pattern such that concatenating that pattern repeatedly recreates the entire string exactly. For example, consider the string "abab" : The substring "ab" repeated twice...

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LeetCode 409 - Longest Palindrome

LeetCode Problem 409 Difficulty: 🟢 Easy Topics: Hash Table, String, Greedy Solution Problem Understanding The problem asks us to find the length of the longest palindrome that can be constructed using the characters of a given string s . A palindrome is a string that reads the same forwards and backwards. The input string s contains only lowercase and uppercase English letters, and letter case matters, so 'A' and 'a'...

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LeetCode 1113 - Reported Posts

LeetCode Problem 1113 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to determine the number of posts that were reported yesterday grouped by the reason for the report. We are given an Actions table where each row represents a user performing an action on a post, with the action type recorded in the action column and optional extra information in the extra column. In this...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 175 - Combine Two Tables

LeetCode Problem 175 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to combine two relational database tables, Person and Address , in such a way that we report each person's first name, last name, city, and state. The Person table contains identifiers and names of people, while the Address table contains identifiers, the corresponding personId , and the city and state of that person. Importantly,...

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LeetCode 744 - Find Smallest Letter Greater Than Target

LeetCode Problem 744 Difficulty: 🟢 Easy Topics: Array, Binary Search Solution Problem Understanding The problem gives us a sorted array of lowercase English letters and a target character. Our task is to find the smallest character in the array that is strictly greater than the target character in lexicographical order. Lexicographical order for characters is simply alphabetical order. For example, 'f' is greater than 'c' , and 'x' is greater...

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LeetCode 1323 - Maximum 69 Number

LeetCode Problem 1323 Difficulty: 🟢 Easy Topics: Math, Greedy Solution Problem Understanding The problem gives us a positive integer num that contains only the digits 6 and 9 . We are allowed to change at most one digit , where a 6 can become a 9 , or a 9 can become a 6 . Our goal is to return the largest possible number after making zero or one modification....

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LeetCode 263 - Ugly Number

LeetCode Problem 263 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine whether a given integer n is an ugly number. An ugly number is defined as a positive integer whose prime factors are limited to only 2 , 3 , and 5 . This means that after completely factoring the number into primes, every prime factor must belong to the set {2, 3, 5}...

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LeetCode 1812 - Determine Color of a Chessboard Square

LeetCode Problem 1812 Difficulty: 🟢 Easy Topics: Math, String Solution LeetCode 1812 - Determine Color of a Chessboard Square Problem Understanding This problem asks us to determine whether a given chessboard square is white or black based on its coordinate. The input is a string of length two, where the first character is a lowercase letter from 'a' to 'h' , representing the column, and the second character is a...

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LeetCode 897 - Increasing Order Search Tree

LeetCode Problem 897 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root of a Binary Search Tree, abbreviated as BST, and asks us to rearrange the tree into a very specific form. A Binary Search Tree has the property that for every node: All values in the left subtree are smaller All values in the right subtree...

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LeetCode 1592 - Rearrange Spaces Between Words

LeetCode Problem 1592 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem requires rearranging spaces in a given string text so that all words are separated by the maximum possible equal number of spaces , and any leftover spaces are placed at the end of the string. The input text consists of lowercase English letters and spaces, and it is guaranteed to contain at least one word , which...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 607 - Sales Person

LeetCode Problem 607 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to find the names of all salespeople who have never handled an order for the company named "RED" . We are given three database tables: SalesPerson contains information about each salesperson, including their unique sales_id and name . Company contains company information, including com_id and company name . Orders records every order, linking a salesperson...

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LeetCode 1716 - Calculate Money in Leetcode Bank

LeetCode Problem 1716 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem describes a repeating weekly saving pattern. Hercy deposits money into the LeetCode bank every day, and the amount increases in a structured way. On the very first Monday, he deposits 1 dollar. Each following day in the same week increases by 1 . That means the first week looks like this: Monday: 1 Tuesday: 2 Wednesday: 3...

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LeetCode 800 - Similar RGB Color

LeetCode Problem 800 Difficulty: 🟢 Easy Topics: Math, String, Enumeration Solution Problem Understanding The problem is asking us to find the shorthand RGB color that is most similar to a given full-length RGB color string. An RGB color is represented as a hexadecimal string of the form "#RRGGBB" , where each pair of characters ( RR , GG , BB ) represents the red, green, and blue components, respectively, using...

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LeetCode 1460 - Make Two Arrays Equal by Reversing Subarrays

LeetCode Problem 1460 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding This problem asks whether one integer array, arr , can be transformed into another array, target , by repeatedly reversing any non-empty contiguous subarray. A subarray reversal means choosing a continuous segment of the array and reversing the order of its elements. For example, reversing [2,4,1] changes it into [1,4,2] . The key detail is that...

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LeetCode 1572 - Matrix Diagonal Sum

LeetCode Problem 1572 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem gives us a square matrix mat of size n x n . A square matrix means the number of rows and columns are the same. We must calculate the sum of all elements that belong to either of the two diagonals. The primary diagonal contains elements where the row index and column index are equal: mat[i][i]...

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LeetCode 1742 - Maximum Number of Balls in a Box

LeetCode Problem 1742 Difficulty: 🟢 Easy Topics: Hash Table, Math, Counting Solution Problem Understanding The problem describes a scenario in which you have a sequence of balls numbered consecutively from lowLimit to highLimit , inclusive. Each ball must be placed into a box, where the box number is determined by the sum of the digits of the ball’s number. For example, ball 321 goes into box 3 + 2 +...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 613 - Shortest Distance in a Line

LeetCode Problem 613 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 613, Shortest Distance in a Line Problem Understanding This problem gives us a database table named Point that contains integer coordinates on the X-axis. Each row represents one point, and the column x is unique because it is the primary key. The task is to compute the smallest absolute distance between any two points in the table. Mathematically, for every...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1385 - Find the Distance Value Between Two Arrays

LeetCode Problem 1385 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Binary Search, Sorting Solution Problem Understanding The problem is asking us to compute the distance value between two arrays arr1 and arr2 given a threshold d . Specifically, the distance value is defined as the count of elements in arr1 for which no element in arr2 is within a distance of d , i.e., there is no arr2[j] such that...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1084 - Sales Analysis III

LeetCode Problem 1084 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to identify products that were sold only during the first quarter of 2019, meaning between 2019-01-01 and 2019-03-31 , inclusive. We are provided with two tables: Product and Sales . The Product table lists all products along with their IDs and unit prices, while the Sales table lists individual sales transactions with the product_id ,...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1431 - Kids With the Greatest Number of Candies

LeetCode Problem 1431 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding This problem asks us to determine which children could potentially have the greatest number of candies if we distribute a fixed number of extra candies to any single child. The input is an array candies where each element represents the number of candies a particular child has, and an integer extraCandies that represents additional candies that can be given....

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LeetCode 1779 - Find Nearest Point That Has the Same X or Y Coordinate

LeetCode Problem 1779 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives your current position on a 2D Cartesian grid as (x, y) and a list of other points. Each point is represented as [ai, bi] . A point is considered valid if it shares either: the same x-coordinate as your location, meaning ai == x the same y-coordinate as your location, meaning bi == y Among all...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 21 - Merge Two Sorted Lists

LeetCode Problem 21 Difficulty: 🟢 Easy Topics: Linked List, Recursion Solution Problem Understanding This problem asks us to merge two already sorted singly linked lists into one new sorted linked list. The important detail is that we are not creating entirely new nodes for the merged result. Instead, we reuse the existing nodes by reconnecting their next pointers. Each input list is sorted in non-decreasing order. That means values can...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 944 - Delete Columns to Make Sorted

LeetCode Problem 944 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem gives us an array of strings where every string has exactly the same length. If we place all strings vertically, character by character, the strings form a rectangular grid. For example, given: ["abc", "bce", "cae"] the grid becomes: abc bce cae Each column is formed by taking characters from the same index across all rows. The...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 653 - Two Sum IV - Input is a BST

LeetCode Problem 653 Difficulty: 🟢 Easy Topics: Hash Table, Two Pointers, Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution LeetCode 653, Two Sum IV - Input is a BST Problem Understanding This problem gives us the root of a Binary Search Tree (BST) and an integer k . We must determine whether there are two distinct nodes in the tree whose values add up to k ....

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LeetCode 628 - Maximum Product of Three Numbers

LeetCode Problem 628 Difficulty: 🟢 Easy Topics: Array, Math, Sorting Solution Problem Understanding The problem gives an integer array nums and asks us to select exactly three numbers whose product is as large as possible. We must return that maximum product value. In simpler terms, among all possible combinations of three elements in the array, we need to determine which combination produces the greatest multiplication result. The input is an...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1303 - Find the Team Size

LeetCode Problem 1303 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Employee , where every row represents a single employee and the team they belong to. The table contains two columns: Column Meaning employee_id Unique identifier for an employee team_id Identifier of the team the employee belongs to The task is to compute the size of each employee's team. In other words, for...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1069 - Product Sales Analysis II

LeetCode Problem 1069 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the total quantity sold for each product based on records in the Sales table. The Sales table contains transaction level information. Each row represents a sale of a specific product in a given year, along with the quantity sold and the unit price. Since a product can appear in multiple rows, potentially across...

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LeetCode 922 - Sort Array By Parity II

LeetCode Problem 922 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Sorting Solution Problem Understanding The problem gives an integer array nums where exactly half of the elements are even numbers and the other half are odd numbers. The task is to rearrange the array so that every even index contains an even number and every odd index contains an odd number. In other words: If an index i is even,...

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LeetCode 1502 - Can Make Arithmetic Progression From Sequence

LeetCode Problem 1502 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem asks us to determine whether the elements of a given array can be rearranged so that they form an arithmetic progression. An arithmetic progression is a sequence where the difference between every pair of consecutive elements is the same. For example, [1, 3, 5, 7] is an arithmetic progression because every adjacent difference is 2 ....

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LeetCode 226 - Invert Binary Tree

LeetCode Problem 226 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives the root node of a binary tree and asks us to invert the tree. Inverting a binary tree means swapping the left and right child of every node in the tree. For example, if a node originally has: left child = 2 right child = 7 after inversion it becomes:...

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LeetCode 183 - Customers Who Never Order

LeetCode Problem 183 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem is asking us to identify all customers from a Customers table who have never placed an order according to the Orders table. In other words, we are looking for entries in Customers that do not have a corresponding customerId in the Orders table. The input consists of two tables: Customers and Orders . Customers has an id...

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LeetCode 1228 - Missing Number In Arithmetic Progression

LeetCode Problem 1228 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to find a missing value from an array that originally formed an arithmetic progression (AP). An arithmetic progression is a sequence where the difference between consecutive terms is constant, i.e., arr[i + 1] - arr[i] is the same for every consecutive pair. We are given an array arr where one element has been removed...

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LeetCode 671 - Second Minimum Node In a Binary Tree

LeetCode Problem 671 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem provides a special binary tree where each node either has zero or two children, and every internal node has a value equal to the smaller value among its two children. This property guarantees that the root contains the minimum value in the tree , since the root is always the smallest among its...

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LeetCode 1389 - Create Target Array in the Given Order

LeetCode Problem 1389 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding This problem asks us to build a new array called target by following a sequence of insertion operations. We are given two arrays, nums and index , where both arrays have the same length. At each position i , the value nums[i] must be inserted into the target array at position index[i] . The important detail is that...

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LeetCode 1370 - Increasing Decreasing String

LeetCode Problem 1370 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem requires us to reorder a string s by repeatedly picking characters in a specific increasing and decreasing pattern. In other words, we need to simulate a process where, at each iteration, we first pick the smallest character and keep picking increasingly larger characters until we cannot pick anymore. Then, we switch directions: we pick...

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LeetCode 1417 - Reformat The String

LeetCode Problem 1417 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us an alphanumeric string s that contains only lowercase English letters and digits. Our task is to rearrange the characters so that no two adjacent characters belong to the same category. In other words, every letter must be next to a digit, and every digit must be next to a letter. The important detail is that...

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LeetCode 1251 - Average Selling Price

LeetCode Problem 1251 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the average selling price for every product based on two tables: Prices and UnitsSold . The Prices table tells us how much a product costs during a specific date range. Each row contains a product_id , a start_date , an end_date , and the price for that period. A product may have multiple...

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LeetCode 1196 - How Many Apples Can You Put into the Basket

LeetCode Problem 1196 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution Problem Understanding This problem is asking us to determine how many apples we can fit into a basket with a maximum carrying capacity of 5000 units of weight. We are given an array weight where each element represents the weight of a single apple. The goal is to maximize the number of apples placed into the basket without exceeding...

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LeetCode 1629 - Slowest Key

LeetCode Problem 1629 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding This problem asks us to determine which key on a keypad was pressed for the longest duration during a test sequence. We are given two pieces of information: a list of releaseTimes indicating when each key was released, and a string keysPressed representing the keys pressed in order. The first key is considered pressed at time 0, and...

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LeetCode 520 - Detect Capital

LeetCode Problem 520 Difficulty: 🟢 Easy Topics: String Solution only conditions are satisfied.

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LeetCode 1018 - Binary Prefix Divisible By 5

LeetCode Problem 1018 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem presents a binary array nums , where each element is either 0 or 1 . We are asked to compute the sequence of numbers formed by interpreting the subarray nums[0..i] as a binary number, denoted as xi . The task is to return a boolean array indicating, for each i , whether xi is divisible...

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LeetCode 342 - Power of Four

LeetCode Problem 342 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation, Recursion Solution LeetCode 342 - Power of Four Problem Understanding This problem asks us to determine whether a given integer n is an exact power of four. In other words, we need to check whether there exists some integer x such that: n = 4^x Examples of powers of four are: 1 = 4^0 4 = 4^1 16 = 4^2...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 989 - Add to Array-Form of Integer

LeetCode Problem 989 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem is asking us to perform addition between a number represented as an array of digits, num , and an integer k . The array-form of a number represents each digit in left-to-right order, so the first element corresponds to the most significant digit. For example, [1, 2, 0, 0] represents the number 1200 . Given num...

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LeetCode 1413 - Minimum Value to Get Positive Step by Step Sum

LeetCode Problem 1413 Difficulty: 🟢 Easy Topics: Array, Prefix Sum Solution Problem Understanding The problem gives us an integer array nums and asks us to determine the minimum positive starting value such that when we repeatedly add elements from nums to this starting value, the running total never drops below 1 . In other words, imagine we begin with some number called startValue . We process the array from left...

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LeetCode 1022 - Sum of Root To Leaf Binary Numbers

LeetCode Problem 1022 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem gives us the root of a binary tree where every node contains either 0 or 1 . Each path from the root node to a leaf node represents a binary number, where the root contributes the most significant bit and each child adds another bit to the right. For example, consider a path:...

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LeetCode 1646 - Get Maximum in Generated Array

LeetCode Problem 1646 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem asks us to generate an array called nums using a specific set of rules, then return the maximum value that appears in that array. The array has length n + 1 , meaning its valid indices range from 0 to n . The generation rules define how each element is computed based on previously computed elements....

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LeetCode 507 - Perfect Number

LeetCode Problem 507 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding This problem asks us to determine whether a given positive integer num is a perfect number . A perfect number is defined as a number whose sum of positive divisors, excluding the number itself , equals the number. In other words, we must find all integers that divide num evenly, excluding num , sum them up, and check whether...

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LeetCode 598 - Range Addition II

LeetCode Problem 598 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem presents an m x n matrix M initialized with all zeros. You are also given an array of operations ops , where each operation ops[i] = [ai, bi] instructs you to increment by one all elements in the submatrix defined by the top-left corner (0,0) and the bottom-right corner (ai-1, bi-1) . After applying all operations,...

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LeetCode 1160 - Find Words That Can Be Formed by Characters

LeetCode Problem 1160 Difficulty: 🟢 Easy Topics: Array, Hash Table, String, Counting Solution Problem Understanding This problem asks us to determine which words from a given list can be constructed using the characters available in another string, chars . A word is considered good if every character it needs exists in chars in sufficient quantity. Importantly, characters in chars can only be used once per word , meaning repeated letters...

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LeetCode 1450 - Number of Students Doing Homework at a Given Time

LeetCode Problem 1450 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding This problem asks us to determine how many students are doing homework at a specific point in time, given arrays representing when each student starts and finishes their homework. More concretely, we have two arrays startTime and endTime of the same length. Each index i represents one student: startTime[i] is when they begin, and endTime[i] is when they finish....

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LeetCode 20 - Valid Parentheses

LeetCode Problem 20 Difficulty: 🟢 Easy Topics: String, Stack Solution Problem Understanding The problem gives a string containing only six possible characters: ( , ) , { , } , [ and ] . Each opening bracket must eventually be matched with the correct closing bracket, and the order of matching matters. A string is considered valid only if every opening bracket is closed by the same type of bracket...

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LeetCode 1725 - Number Of Rectangles That Can Form The Largest Square

LeetCode Problem 1725 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 1725 - Number Of Rectangles That Can Form The Largest Square Problem Understanding The problem gives us a list of rectangles, where each rectangle is represented as [li, wi] . Here, li is the rectangle's length and wi is its width. From each rectangle, we want to determine the largest square that can be cut from it. A square requires...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 762 - Prime Number of Set Bits in Binary Representation

LeetCode Problem 762 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation Solution Problem Understanding The problem requires counting the numbers within a given inclusive range [left, right] that have a prime number of set bits in their binary representation. The set bits of a number refer to the number of 1 s in its binary representation. For example, the number 6 in binary is 110 , which has 2 set bits....

Practice › LeetCode › LeetCode 01xx ›

LeetCode 171 - Excel Sheet Column Number

LeetCode Problem 171 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding This problem asks us to convert an Excel-style column title into its corresponding numerical index. In Excel spreadsheets, columns are labeled alphabetically: A -> 1 B -> 2 ... Z -> 26 AA -> 27 AB -> 28 The labeling system works similarly to a positional number system, except instead of digits 0-9 , it uses letters A-Z...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 872 - Leaf-Similar Trees

LeetCode Problem 872 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to compare two binary trees based only on their leaf nodes. A leaf node is a node that has no left child and no right child. For each tree, we must collect the leaf values in left to right order, then determine whether the two resulting sequences are identical. The important...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 136 - Single Number

LeetCode Problem 136 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem gives an integer array nums where every value appears exactly twice except for one value that appears only once. The task is to find and return that unique value. The important part of the problem is not just finding the unique number, but doing so under strict constraints. The solution must run in linear time,...

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LeetCode 1327 - List the Products Ordered in a Period

LeetCode Problem 1327 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to list all products that have been ordered in February 2020 with a total quantity of at least 100 units. We are given two tables: Products and Orders . The Products table contains metadata about each product including its unique product_id and product_name . The Orders table records every order of products with the product_id...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1122 - Relative Sort Array

LeetCode Problem 1122 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Counting Sort Solution Problem Understanding This problem asks us to sort arr1 , but not in ordinary ascending or descending order. Instead, the sorting order is partially dictated by another array, arr2 . The key requirement is that every number appearing in arr2 must appear in arr1 in exactly the same relative order. If a number appears multiple times...

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LeetCode 1795 - Rearrange Products Table

LeetCode Problem 1795 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The Products table stores product prices across three different stores. Each row represents one product, identified by product_id , and each store column contains the product's price in that specific store. The table has this structure: Column Meaning product_id Unique identifier for the product store1 Price of the product in store1 store2 Price of the product in store2 store3...

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LeetCode 1103 - Distribute Candies to People

LeetCode Problem 1103 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem describes a sequential candy distribution process across a row of people. We are given two integers, candies and num_people . The goal is to simulate distributing candies in increasing order until all candies are exhausted. The distribution pattern follows a strict sequence. The first person receives 1 candy, the second person receives 2 candies, the third...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 876 - Middle of the Linked List

LeetCode Problem 876 Difficulty: 🟢 Easy Topics: Linked List, Two Pointers Solution Problem Understanding The problem gives us the head of a singly linked list and asks us to return the middle node. A singly linked list is a sequence of nodes where each node contains a value and a pointer to the next node. Unlike arrays, linked lists do not support direct indexing, so we cannot instantly jump to...

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LeetCode 1154 - Day of the Year

LeetCode Problem 1154 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to compute the ordinal day number of a year given a date in the format YYYY-MM-DD . For example, January 1st is always day 1, January 2nd is day 2, and December 31st is either day 365 or 366 depending on whether the year is a leap year. The input is a string that...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 217 - Contains Duplicate

LeetCode Problem 217 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem gives an integer array nums and asks whether any number appears more than once. If at least one value is repeated, we return true . If every value appears exactly once, we return false . The input is a list of integers. The output is a boolean value that answers a simple question: does...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1165 - Single-Row Keyboard

LeetCode Problem 1165 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem describes a single-row keyboard where each key is positioned at a unique index from 0 to 25. You are given a string keyboard of length 26 that specifies the layout of all lowercase English letters. The initial finger position is at index 0, and moving the finger from index i to index j takes |i...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1173 - Immediate Food Delivery I

LeetCode Problem 1173 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking to calculate the percentage of immediate food deliveries from a delivery table. An immediate delivery is defined as one where the customer_pref_delivery_date matches the order_date . The input is a table named Delivery with columns delivery_id , customer_id , order_date , and customer_pref_delivery_date . Each row represents a single delivery order with its preferred delivery...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1475 - Final Prices With a Special Discount in a Shop

LeetCode Problem 1475 Difficulty: 🟢 Easy Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem presents a scenario where you are buying items in a shop, each with a given price stored in an array prices . For each item at index i , there may exist a discount based on the next item j (where j > i ) such that prices[j] <= prices[i] . If such a...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 589 - N-ary Tree Preorder Traversal

LeetCode Problem 589 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search Solution Problem Understanding The problem asks for a preorder traversal of an n-ary tree. In a preorder traversal, the order of visiting nodes is: first the root node, then recursively all the children from left to right. The input is given as the root node of an n-ary tree, where each node has a value and a list of...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2229 - Check if an Array Is Consecutive

LeetCode Problem 2229 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem asks us to determine whether an integer array forms a perfect sequence of consecutive numbers without gaps or duplicates. More formally, if the array has length n and its minimum value is x , then the array is considered consecutive if it contains every integer in the range: $$[x, x + n - 1]$$...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1313 - Decompress Run-Length Encoded List

LeetCode Problem 1313 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 1313, Decompress Run-Length Encoded List Problem Understanding This problem asks us to reconstruct an array that was compressed using a simple run-length encoding format. The input array nums always contains an even number of elements. Every two consecutive elements form a pair: The first value represents a frequency, called freq The second value represents a number, called val For every...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1114 - Print in Order

LeetCode Problem 1114 Difficulty: 🟢 Easy Topics: Concurrency Solution Problem Understanding This problem asks us to coordinate three independent threads so that they execute in a strict order, regardless of how the operating system schedules them. We are given a class with three methods, first() , second() , and third() . Each method is called by a different thread, and the threads may start in any order. The goal is...

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LeetCode 1351 - Count Negative Numbers in a Sorted Matrix

LeetCode Problem 1351 Difficulty: 🟢 Easy Topics: Array, Binary Search, Matrix Solution Problem Understanding The problem asks us to count all the negative numbers in a 2D matrix grid where each row and column is sorted in non-increasing order . In other words, values decrease or stay the same as you move to the right in a row and downward in a column. The input is a matrix of integers,...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1672 - Richest Customer Wealth

LeetCode Problem 1672 Difficulty: 🟢 Easy Topics: Array, Matrix Solution LeetCode 1672 - Richest Customer Wealth Problem Understanding This problem gives us a two dimensional integer array called accounts . Each row represents a customer, and each column represents one of that customer's bank accounts. The value accounts[i][j] represents how much money the i-th customer has in the j-th bank account. Our task is to compute the total wealth of...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 225 - Implement Stack using Queues

LeetCode Problem 225 Difficulty: 🟢 Easy Topics: Stack, Design, Queue Solution Problem Understanding The problem asks us to implement a stack data structure while using only queue operations internally. A stack follows the Last-In-First-Out, or LIFO, principle. This means the most recently inserted element must be removed first. In contrast, a queue follows the First-In-First-Out, or FIFO, principle, where elements leave in the same order they entered. We must design...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 412 - Fizz Buzz

LeetCode Problem 412 Difficulty: 🟢 Easy Topics: Math, String, Simulation Solution LeetCode 412, Fizz Buzz Problem Understanding The problem asks us to generate a list of strings for all integers from 1 to n . For each number, we apply a set of divisibility rules: If the number is divisible by both 3 and 5 , we append "FizzBuzz" . If the number is divisible only by 3 , we...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1356 - Sort Integers by The Number of 1 Bits

LeetCode Problem 1356 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation, Sorting, Counting Solution Problem Understanding The problem asks us to sort an integer array arr based on the number of 1 bits in the binary representation of each element. This means that we are not sorting by the integer value itself but by the count of 1 s in its binary form. If two numbers have the same number of...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1394 - Find Lucky Integer in an Array

LeetCode Problem 1394 Difficulty: 🟢 Easy Topics: Array, Hash Table, Counting Solution Problem Understanding This problem asks us to identify a special number in an array called a lucky integer . A lucky integer is defined as an integer in the array whose frequency exactly matches its value. For example, if the number 3 appears exactly 3 times in the array, it is considered lucky. Our task is to find...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 283 - Move Zeroes

LeetCode Problem 283 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding The problem gives us an integer array nums and asks us to move every 0 element to the end of the array while preserving the relative order of all non-zero elements. The phrase "relative order" is extremely important. It means that if the non-zero numbers originally appear in a certain sequence, they must remain in that same...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1005 - Maximize Sum Of Array After K Negations

LeetCode Problem 1005 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting Solution Problem Understanding The problem is asking us to maximize the sum of an integer array after performing exactly k negations. A negation operation consists of picking an index i and replacing nums[i] with -nums[i] . This operation can be applied to the same element multiple times. The input consists of an array of integers nums and an integer k...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1075 - Project Employees I

LeetCode Problem 1075 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 1075, Project Employees I Problem Understanding This problem provides two database tables, Project and Employee . The Project table represents which employees are assigned to which projects. Each row contains a project_id and an employee_id . Since the pair (project_id, employee_id) is the primary key, the same employee cannot appear more than once for the same project. The Employee table...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1656 - Design an Ordered Stream

LeetCode Problem 1656 Difficulty: 🟢 Easy Topics: Array, Hash Table, Design, Data Stream Solution Problem Understanding This problem asks us to simulate a data stream where each element arrives with a unique ID in arbitrary order. Each element consists of an integer idKey (between 1 and n ) and a string value . The goal is to design a stream that, after every insertion, returns the largest contiguous chunk of...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1598 - Crawler Log Folder

LeetCode Problem 1598 Difficulty: 🟢 Easy Topics: Array, String, Stack Solution Problem Understanding In this problem, we are simulating navigation inside a file system. The system starts at the main folder, and we are given a sequence of folder navigation operations. Each operation changes the current directory in one of three ways. The operation "../" means moving up to the parent directory. However, if we are already at the main...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1758 - Minimum Changes To Make Alternating Binary String

LeetCode Problem 1758 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a binary string s , which means the string contains only the characters '0' and '1' . In one operation, we are allowed to flip a character, meaning we can change '0' into '1' or '1' into '0' . Our goal is to transform the string into an alternating binary string using the minimum number...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 657 - Robot Return to Origin

LeetCode Problem 657 Difficulty: 🟢 Easy Topics: String, Simulation Solution Problem Understanding This problem asks us to determine whether a robot, starting at the origin (0, 0) on a 2D plane, returns to the origin after executing a sequence of moves. Each move is represented by a character in a string: 'R' moves right, 'L' moves left, 'U' moves up, and 'D' moves down. The robot always moves exactly one...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 929 - Unique Email Addresses

LeetCode Problem 929 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding The problem gives us a list of email addresses and asks how many unique destinations actually receive emails after applying Gmail-like normalization rules. Each email consists of two parts separated by the '@' symbol: The local name, which appears before '@' The domain name, which appears after '@' The domain name is always preserved exactly as...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1791 - Find Center of Star Graph

LeetCode Problem 1791 Difficulty: 🟢 Easy Topics: Graph Theory Solution Problem Understanding The problem is asking us to identify the center node of a star graph. A star graph is a very specific type of graph with n nodes: there is one node called the center , and it is connected to all other n-1 nodes. Every other node in the graph has exactly one connection , which is to...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1560 - Most Visited Sector in a Circular Track

LeetCode Problem 1560 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding In this problem, we are given a circular track divided into n sectors, numbered from 1 to n . A marathon runner moves around this track in increasing numerical order, and after sector n , the runner wraps back to sector 1 . The input array rounds describes the sequence of rounds in the marathon. Each consecutive pair...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1064 - Fixed Point

LeetCode Problem 1064 Difficulty: 🟢 Easy Topics: Array, Binary Search Solution Problem Understanding The problem is asking us to find a "fixed point" in a sorted array of distinct integers . A fixed point is an index i such that the value at that index equals the index itself, i.e., arr[i] == i . The input is an array arr of integers sorted in ascending order , and we need...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 859 - Buddy Strings

LeetCode Problem 859 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks whether it is possible to make two strings equal by performing exactly one swap operation on the first string s . A swap operation means choosing two different indices i and j in s and exchanging the characters at those positions. After performing that single swap, the resulting string must match goal . The...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 965 - Univalued Binary Tree

LeetCode Problem 965 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution LeetCode 965 - Univalued Binary Tree Problem Understanding The problem gives us the root node of a binary tree and asks whether the tree is "uni-valued". A binary tree is considered uni-valued if every node in the tree contains exactly the same integer value. In simpler terms, we need to examine every node in the...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1683 - Invalid Tweets

LeetCode Problem 1683 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem gives us a database table named Tweets with two columns: Column Description tweet_id Unique identifier for each tweet content The text content of the tweet The task is to return the IDs of all invalid tweets. A tweet is considered invalid if the number of characters in its content is strictly greater than 15 . In other...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1304 - Find N Unique Integers Sum up to Zero

LeetCode Problem 1304 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to construct an array containing exactly n unique integers whose total sum is equal to 0 . The keyword any is important here because the problem does not require a specific arrangement or a lexicographically smallest answer. As long as the integers are unique and their sum equals zero, the solution is valid. The...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 747 - Largest Number At Least Twice of Others

LeetCode Problem 747 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem gives us an integer array nums in which the largest value is guaranteed to be unique. Our task is to determine whether this largest number is at least twice as large as every other number in the array. If that condition is satisfied, we return the index of the largest element. Otherwise, we return -1 ....

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1565 - Unique Orders and Customers Per Month

LeetCode Problem 1565 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem requires analyzing a table of orders to calculate monthly statistics. Specifically, for each unique month present in the Orders table, we need to determine two metrics: the number of unique orders and the number of unique customers whose orders have an invoice greater than 20. The input consists of a table with four columns: order_id (unique identifier),...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1217 - Minimum Cost to Move Chips to The Same Position

LeetCode Problem 1217 Difficulty: 🟢 Easy Topics: Array, Math, Greedy Solution Problem Understanding The problem asks us to move n chips located at various positions along a one-dimensional line so that they all end up at the same position. Each chip can be moved either by 2 units at zero cost or by 1 unit at a cost of 1. The input is an array of integers, position , where...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1608 - Special Array With X Elements Greater Than or Equal X

LeetCode Problem 1608 Difficulty: 🟢 Easy Topics: Array, Binary Search, Sorting Solution Problem Understanding The problem gives us an array nums containing non-negative integers. We need to determine whether there exists an integer x such that exactly x elements in the array are greater than or equal to x . The important detail is that x does not need to appear inside the array itself. We are only concerned with...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1571 - Warehouse Manager

LeetCode Problem 1571 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the total storage volume occupied by products inside each warehouse. We are given two database tables: The Warehouse table tells us which products are stored in each warehouse and how many units of each product exist there. Warehouse(name, product_id, units) The Products table stores the physical dimensions of every product. Products(product_id, product_name, Width,...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 14 - Longest Common Prefix

LeetCode Problem 14 Difficulty: 🟢 Easy Topics: Array, String, Trie Solution LeetCode 14, Longest Common Prefix Problem Understanding The problem gives an array of strings and asks us to find the longest prefix shared by every string in the array. A prefix is a sequence of characters that appears at the beginning of a string. For example, "fl" is a prefix of "flower" and "flow" because both strings start with...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1346 - Check If N and Its Double Exist

LeetCode Problem 1346 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Binary Search, Sorting Solution Problem Understanding The problem gives an integer array arr and asks whether there exist two different indices i and j such that: arr[i] == 2 * arr[j] In simpler terms, we need to determine whether one number in the array is exactly double another number in the same array. The indices must be different,...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1133 - Largest Unique Number

LeetCode Problem 1133 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem is asking us to identify the largest integer in an array that occurs exactly once. In other words, among all integers that are unique (appear only one time), we need to find the maximum. If no such integer exists, the output should be -1 . The input nums is a list of integers, each...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1800 - Maximum Ascending Subarray Sum

LeetCode Problem 1800 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives an array of positive integers called nums . We must find the contiguous subarray that is strictly increasing and has the largest possible sum. A subarray is contiguous, which means the elements must appear next to each other in the original array. We are not allowed to skip elements. The phrase "strictly increasing" means every element...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1652 - Defuse the Bomb

LeetCode Problem 1652 Difficulty: 🟢 Easy Topics: Array, Sliding Window Solution Problem Understanding The problem gives us a circular array called code and an integer k . We must produce a new array where each element is replaced according to the value of k . If k > 0 , each element becomes the sum of the next k elements in the circular array. If k < 0 , each...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1588 - Sum of All Odd Length Subarrays

LeetCode Problem 1588 Difficulty: 🟢 Easy Topics: Array, Math, Prefix Sum Solution Problem Understanding The problem asks us to calculate the sum of all odd-length subarrays of a given array of positive integers. A subarray is any contiguous sequence of elements from the original array. For example, in an array [1, 2, 3] , the subarrays of length 1 are [1] , [2] , [3] , and the subarray of...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1083 - Sales Analysis II

LeetCode Problem 1083 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify all buyers who purchased the product named S8 but never purchased the product named iPhone . We are given two tables: The Product table stores information about products. Each row contains a unique product_id , the product name, and its unit price. The Sales table stores sales transactions. Each row represents a purchase...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 414 - Third Maximum Number

LeetCode Problem 414 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem asks us to find the third distinct maximum number in an integer array. The key word is distinct. Duplicate values should only be counted once when determining rankings. For example, in the array [2,2,3,1] , the distinct values are {3,2,1} . Even though 2 appears twice, it only counts as one distinct number. The third distinct...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1729 - Find Followers Count

LeetCode Problem 1729 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to determine, for each user in a social media application, how many followers they have. The input is a table called Followers with two columns: user_id and follower_id . Each row represents a relationship where follower_id follows user_id . The combination (user_id, follower_id) is unique, so there are no duplicate follower entries for a...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1184 - Distance Between Bus Stops

LeetCode Problem 1184 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding In this problem, we are given a circular bus route with n stops numbered from 0 to n - 1 . The array distance describes the distance between neighboring stops. Specifically, distance[i] represents the distance from stop i to stop (i + 1) % n . Because the route is circular, the bus can travel in two possible directions...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 389 - Find the Difference

LeetCode Problem 389 Difficulty: 🟢 Easy Topics: Hash Table, String, Bit Manipulation, Sorting Solution Problem Understanding This problem gives us two strings, s and t . The string t is created by taking all characters from s , shuffling them into a different order, and then inserting exactly one additional character somewhere in the string. Our task is to identify and return that extra character. In other words, every character...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 734 - Sentence Similarity

LeetCode Problem 734 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding The problem gives us two sentences, where each sentence is represented as an array of words. We are also given a list of word pairs that define which words are considered similar. Our task is to determine whether the two sentences are similar according to the following rules: The sentences must contain the same number of...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1380 - Lucky Numbers in a Matrix

LeetCode Problem 1380 Difficulty: 🟢 Easy Topics: Array, Matrix Solution LeetCode 1380 - Lucky Numbers in a Matrix Problem Understanding This problem asks us to identify all lucky numbers in a given matrix. A lucky number is defined as a value that satisfies two conditions simultaneously : It must be the minimum value in its row It must be the maximum value in its column We are given an m...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1752 - Check if Array Is Sorted and Rotated

LeetCode Problem 1752 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem is asking us to determine whether a given array nums could be the result of taking a sorted array in non-decreasing order and then rotating it by some number of positions. A non-decreasing array is one where each element is greater than or equal to the previous one. Rotating an array means taking some prefix of elements...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 883 - Projection Area of 3D Shapes

LeetCode Problem 883 Difficulty: 🟢 Easy Topics: Array, Math, Geometry, Matrix Solution Problem Understanding The problem gives us an n x n matrix called grid . Each cell grid[i][j] represents how many 1 x 1 x 1 cubes are stacked vertically at position (i, j) on a flat surface. We must calculate the total area of the projections of this 3D structure onto three planes: The xy plane, which is...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 941 - Valid Mountain Array

LeetCode Problem 941 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to determine whether a given integer array forms a valid mountain array. A mountain array has a very specific structure. The values must first strictly increase until they reach a single peak, then strictly decrease after the peak. More formally, there must exist an index i such that: Everything before i is strictly increasing Everything...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 405 - Convert a Number to Hexadecimal

LeetCode Problem 405 Difficulty: 🟢 Easy Topics: Math, String, Bit Manipulation Solution Problem Understanding The problem asks us to convert a given 32-bit integer num into its hexadecimal representation as a string. Hexadecimal, or base-16, uses digits 0-9 and letters a-f to represent values 0-15 . For positive numbers, the conversion is straightforward: repeatedly divide the number by 16 and map remainders to the hexadecimal digits. For negative numbers, the...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 163 - Missing Ranges

LeetCode Problem 163 Difficulty: 🟢 Easy Topics: Array Solution LeetCode 163 - Missing Ranges Problem Understanding This problem gives us three inputs: A sorted array nums A lower bound lower An upper bound upper The array contains unique integers, and every number in the array lies within the inclusive range [lower, upper] . We must find every number in that range that does not appear in nums . Instead of...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 844 - Backspace String Compare

LeetCode Problem 844 Difficulty: 🟢 Easy Topics: Two Pointers, String, Stack, Simulation Solution LeetCode 844 - Backspace String Compare Problem Understanding This problem asks us to determine whether two strings become identical after processing backspace operations. Each string represents characters typed into a text editor, where the '#' character means "delete the previous character", similar to pressing the backspace key on a keyboard. We are given two input strings, s...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1837 - Sum of Digits in Base K

LeetCode Problem 1837 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem is asking us to convert a given integer n from base 10 into another base k , then compute the sum of its digits in that base. For example, if n is 34 and k is 6, first we convert 34 into base 6, which yields 54 , and then sum the digits: 5 + 4 =...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1281 - Subtract the Product and Sum of Digits of an Integer

LeetCode Problem 1281 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to compute a simple mathematical transformation on the digits of an integer. Given an integer n , we are required to find the product of its digits and the sum of its digits, then return the difference: product - sum . In other words, for a number like 234 , the digits are 2 ,...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1350 - Students With Invalid Departments

LeetCode Problem 1350 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify students who are enrolled in university departments that no longer exist in the department registry. We are given two database tables. The Departments table stores valid university departments, where each department has a unique id and a name . The Students table stores student records, where each student has a unique id ,...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 258 - Add Digits

LeetCode Problem 258 Difficulty: 🟢 Easy Topics: Math, Simulation, Number Theory Solution Problem Understanding The problem asks us to repeatedly transform a number by summing its digits until only a single digit remains. The final single digit should then be returned. For example, if the input is 38 , we first compute 3 + 8 = 11 . Since 11 still has more than one digit, we repeat the process...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1179 - Reformat Department Table

LeetCode Problem 1179 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to take a table Department that records revenue per department per month in a vertical format and convert it into a horizontal format, often called a "pivot" table. In the input, each row contains a department id , a revenue value, and a month . The primary key ensures there is at most one...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1299 - Replace Elements with Greatest Element on Right Side

LeetCode Problem 1299 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us an integer array arr and asks us to replace every element with the greatest value that appears somewhere to its right. The final element in the array has no elements to its right, so it must always become -1 . In other words, for every index i , we want to compute: the maximum value...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 783 - Minimum Distance Between BST Nodes

LeetCode Problem 783 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to find the minimum difference between values of any two nodes in a Binary Search Tree (BST). In other words, given a BST, we need to calculate the smallest absolute difference |a - b| where a and b are values of two distinct nodes. The input...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1518 - Water Bottles

LeetCode Problem 1518 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem is asking us to determine the maximum number of water bottles a person can drink given two integers: numBottles , the initial number of full bottles, and numExchange , the number of empty bottles that can be exchanged for one full bottle. Every time a full bottle is consumed, it becomes an empty bottle that can...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 643 - Maximum Average Subarray I

LeetCode Problem 643 Difficulty: 🟢 Easy Topics: Array, Sliding Window Solution Problem Understanding The problem asks us to find the maximum average value among all contiguous subarrays of a fixed length k . In other words, given an integer array nums , we must examine every possible subarray whose size is exactly k , compute its average, and return the largest average found. A key detail is that the subarray...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1809 - Ad-Free Sessions

LeetCode Problem 1809 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to identify all playback sessions during which no advertisements were shown. We are given two tables: Playback and Ads . The Playback table lists sessions for each customer, with the start and end times of each session. Each session is guaranteed to be non-overlapping for the same customer. The Ads table lists the ads...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1543 - Fix Product Name Format

LeetCode Problem 1543 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to clean and aggregate sales data from a Sales table. Each row contains a unique sale_id , a product_name , and a sale_date . Due to manual data entry errors, product_name may contain extra leading or trailing spaces and may use inconsistent letter casing. Our task is to produce a report that normalizes the product...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1437 - Check If All 1's Are at Least Length K Places Away

LeetCode Problem 1437 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to check whether all 1 s in a given binary array nums are separated by at least k positions. In other words, for any two indices i and j where nums[i] == nums[j] == 1 and i < j , the difference j - i should be at least k + 1 . The input...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1667 - Fix Names in a Table

LeetCode Problem 1667 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Users with two columns: user_id and name . The user_id column uniquely identifies each user, while the name column stores a person's name using a mixture of uppercase and lowercase English letters. The task is to normalize every name so that it follows standard capitalization rules: The first character must be uppercase...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 908 - Smallest Range I

LeetCode Problem 908 Difficulty: 🟢 Easy Topics: Array, Math Solution LeetCode 908 - Smallest Range I Problem Understanding The problem gives us an integer array nums and an integer k . For every element in the array, we are allowed to modify it once by adding any integer value in the range [-k, k] . In other words, each number can either increase by at most k , decrease by...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 111 - Minimum Depth of Binary Tree

LeetCode Problem 111 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine the minimum depth of a binary tree. In other words, given the root of a binary tree, we want to find the shortest path from the root node down to the nearest leaf node. A leaf node is explicitly defined as a node with no children, meaning...

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LeetCode 1056 - Confusing Number

LeetCode Problem 1056 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine whether a given integer becomes a different valid number after being rotated by 180 degrees. Not every digit remains valid after rotation. Only the following mappings are allowed: Original Digit Rotated Digit 0 0 1 1 6 9 8 8 9 6 Digits 2 , 3 , 4 , 5 , and 7...

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LeetCode 705 - Design HashSet

LeetCode Problem 705 Difficulty: 🟢 Easy Topics: Array, Hash Table, Linked List, Design, Hash Function Solution Problem Understanding The problem asks us to design our own HashSet implementation without using any built in hash table libraries such as Python's set or Go's built in map type as the primary solution idea. A HashSet is a data structure that stores unique values. It supports three operations: add(key) , insert a value...

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LeetCode 1189 - Maximum Number of Balloons

LeetCode Problem 1189 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution Problem Understanding The problem asks us to determine the maximum number of times the word "balloon" can be formed using the characters from a given string text . Each character in text can be used at most once per occurrence of the word. The input is a string consisting of only lowercase English letters, with length up to...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 561 - Array Partition

LeetCode Problem 561 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting, Counting Sort Solution Problem Understanding The problem gives an array nums containing 2n integers. Our task is to divide these integers into exactly n pairs. For each pair (ai, bi) , we take the smaller value, min(ai, bi) . After computing the minimum value from every pair, we sum all of those minimums together. The goal is to arrange the...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 326 - Power of Three

LeetCode Problem 326 Difficulty: 🟢 Easy Topics: Math, Recursion Solution LeetCode 326 - Power of Three Problem Understanding The problem asks us to determine whether a given integer n can be represented as a power of three. In mathematical terms, we need to check whether there exists an integer x such that: $$n = 3^x$$ A power of three sequence looks like this: $$1, 3, 9, 27, 81, 243, \dots$$...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 821 - Shortest Distance to a Character

LeetCode Problem 821 Difficulty: 🟢 Easy Topics: Array, Two Pointers, String Solution Problem Understanding The problem gives us a string s and a target character c . For every index in the string, we must compute the distance to the nearest occurrence of c . The distance between two indices is defined as: $$|i - j|$$ where i is the current index and j is the index of some occurrence...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 917 - Reverse Only Letters

LeetCode Problem 917 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem asks us to reverse only the English letters in a string while keeping all non-letter characters fixed in their original positions. In other words, letters move, but symbols, digits, and punctuation marks stay exactly where they started. For example, consider the string "ab-cd" . The letters are "a" , "b" , "c" , and "d"...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 796 - Rotate String

LeetCode Problem 796 Difficulty: 🟢 Easy Topics: String, String Matching Solution Problem Understanding The problem asks us to determine whether one string can be transformed into another string using repeated left rotations. A single shift operation removes the first character of the string and appends it to the end. For example: "abcde" becomes "bcdea" after one shift "bcdea" becomes "cdeab" after another shift We are given two strings, s and...

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LeetCode 119 - Pascal's Triangle II

LeetCode Problem 119 Difficulty: 🟢 Easy Topics: Array, Dynamic Programming Solution LeetCode 119, Pascal's Triangle II Problem Understanding This problem asks us to return a specific row from Pascal's Triangle. The input, rowIndex , represents the zero-based index of the row we want to generate. Pascal's Triangle is a triangular arrangement of numbers where: The first and last number in every row is always 1 Every interior number is the...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 704 - Binary Search

LeetCode Problem 704 Difficulty: 🟢 Easy Topics: Array, Binary Search Solution LeetCode 704, Binary Search Problem Understanding This problem gives us a sorted array of integers named nums and a target integer named target . The array is sorted in ascending order, meaning every element is smaller than the elements that come after it. We must determine whether the target value exists in the array. If it does, we return...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1243 - Array Transformation

LeetCode Problem 1243 Difficulty: 🟢 Easy Topics: Array, Simulation Solution Problem Understanding The problem requires simulating the transformation of an array over consecutive days according to a simple local rule. Each day, every element of the array (except the first and last) is compared with its immediate neighbors. If an element is smaller than both neighbors, it increases by 1. If it is larger than both neighbors, it decreases by...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1708 - Largest Subarray Length K

LeetCode Problem 1708 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding The problem asks us to find the lexicographically largest contiguous subarray of length k from a given array of distinct integers. Two arrays are compared lexicographically. This means we compare elements from left to right until we find the first position where the arrays differ. The array with the larger value at that position is considered larger. For...

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LeetCode 1279 - Traffic Light Controlled Intersection

LeetCode Problem 1279 Difficulty: 🟢 Easy Topics: Concurrency Solution Problem Understanding This problem asks us to design a thread-safe traffic light system for a road intersection where cars arrive concurrently from two different roads. The challenge is not about processing cars sequentially, but about correctly synchronizing multiple threads so that cars from different roads never cross the intersection simultaneously. There are two roads: Road A ( roadId = 1 ),...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 680 - Valid Palindrome II

LeetCode Problem 680 Difficulty: 🟢 Easy Topics: Two Pointers, String, Greedy Solution Problem Understanding The problem asks whether a given string s can become a palindrome after deleting at most one character . A palindrome is a string that reads the same forwards and backwards. For example, "aba" and "racecar" are palindromes because their characters match symmetrically from both ends. The input consists of a single string s made only...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 35 - Search Insert Position

LeetCode Problem 35 Difficulty: 🟢 Easy Topics: Array, Binary Search Solution Problem Understanding The problem gives us a sorted array of distinct integers and a target value. Our task is to determine where the target belongs in the array. If the target already exists, we return its index. If the target does not exist, we return the position where it should be inserted so that the array remains sorted. The...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2011 - Final Value of Variable After Performing Operations

LeetCode Problem 2011 Difficulty: 🟢 Easy Topics: Array, String, Simulation Solution Problem Understanding This problem asks us to simulate a simple programming language with a single integer variable X that starts at 0 . We are given a list of string operations, each of which either increments ( ++X or X++ ) or decrements ( --X or X-- ) the value of X by 1 . The goal is to...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1275 - Find Winner on a Tic Tac Toe Game

LeetCode Problem 1275 Difficulty: 🟢 Easy Topics: Array, Hash Table, Matrix, Simulation Solution Problem Understanding This problem asks us to simulate a game of Tic-Tac-Toe on a 3 x 3 grid given a sequence of moves. Each move specifies the row and column where the current player places their mark. Player A always plays first and uses 'X' , while player B uses 'O' . The goal is to determine...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 590 - N-ary Tree Postorder Traversal

LeetCode Problem 590 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search Solution Problem Understanding This problem asks us to perform a postorder traversal on an n-ary tree. In a binary tree, each node has at most two children. In an n-ary tree, each node can have any number of children. Every node contains a value and a list of child nodes. A postorder traversal means: Visit all children first Then...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1099 - Two Sum Less Than K

LeetCode Problem 1099 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Binary Search, Sorting Solution Problem Understanding This problem asks us to find the maximum sum of any two distinct numbers in an integer array nums such that their sum is strictly less than a given integer k . In other words, we are looking for two indices i and j with i < j where nums[i] + nums[j] is less...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1822 - Sign of the Product of an Array

LeetCode Problem 1822 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to determine the sign of the product of all numbers in an integer array, without necessarily computing the actual product itself. A helper function signFunc(x) is defined as: Return 1 if x > 0 Return -1 if x < 0 Return 0 if x == 0 We are given an array nums , and...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 404 - Sum of Left Leaves

LeetCode Problem 404 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root node of a binary tree and asks us to compute the sum of all left leaves in the tree. A binary tree node may have up to two children, a left child and a right child. A leaf node is a node that has no children at...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 617 - Merge Two Binary Trees

LeetCode Problem 617 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to combine two binary trees into a single merged tree. Each tree consists of nodes where every node contains a value and pointers to a left and right child. The merge process starts from the roots of both trees and proceeds recursively through corresponding positions in the trees. Whenever...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1435 - Create a Session Bar Chart

LeetCode Problem 1435 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Sessions with two columns: Column Meaning session_id Unique identifier for a session duration Length of the session in seconds We need to group sessions into predefined duration ranges, called bins, and count how many sessions fall into each bin. The required bins are: Bin Label Duration Range [0-5> 0 minutes inclusive to...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1607 - Sellers With No Sales

LeetCode Problem 1607 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify all sellers who did not make any sales during the year 2020 . We are given three database tables: The Customer table contains information about customers in the web store. Each customer has a unique customer_id and a customer_name . However, this table is not actually necessary for solving the problem because the...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1378 - Replace Employee ID With The Unique Identifier

LeetCode Problem 1378 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to combine information from two database tables and return the result in a specific format. We are given an Employees table that contains basic employee information, specifically an employee id and name . We are also given an EmployeeUNI table that maps an employee id to a unique_id . The goal is to produce a...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 168 - Excel Sheet Column Title

LeetCode Problem 168 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to convert a positive integer into the column naming format used by Microsoft Excel. Excel labels columns alphabetically instead of numerically. The sequence begins as: 1 -> A 2 -> B ... 26 -> Z 27 -> AA 28 -> AB The input, columnNumber , represents a 1-based column index. Our goal is to...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 392 - Is Subsequence

LeetCode Problem 392 Difficulty: 🟢 Easy Topics: Two Pointers, String, Dynamic Programming Solution Problem Understanding The problem asks whether string s can be formed from string t by deleting some characters from t without changing the order of the remaining characters. A subsequence does not require characters to be adjacent. The only requirement is that the relative ordering stays the same. For example, "abc" is a subsequence of "ahbgdc" because...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1446 - Consecutive Characters

LeetCode Problem 1446 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to compute the power of a string. The power is defined as the length of the longest contiguous substring that contains only one distinct character. In simpler terms, we need to find the longest streak of the same character appearing consecutively in the string. We are not looking for the most frequent character overall, only...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 728 - Self Dividing Numbers

LeetCode Problem 728 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to find all numbers within a given inclusive range [left, right] that satisfy the definition of a self-dividing number. A self-dividing number has two important properties: Every digit inside the number must divide the number evenly. The number cannot contain the digit 0 . For example, consider the number 128 . 128 % 1 ==...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 693 - Binary Number with Alternating Bits

LeetCode Problem 693 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem asks us to determine whether the binary representation of a given positive integer n has alternating bits. In other words, for the binary digits of n , no two consecutive bits should be the same. For example, 101 is alternating, while 111 is not because it contains consecutive ones. The input n is guaranteed to be...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1148 - Article Views I

LeetCode Problem 1148 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to identify all authors who have viewed at least one of their own articles. The input is a database table Views that contains information about articles, their authors, the viewers, and the dates on which the articles were viewed. Each row indicates a single view event, and duplicate rows are possible, meaning the same...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 252 - Meeting Rooms

LeetCode Problem 252 Difficulty: 🟢 Easy Topics: Array, Sorting Solution Problem Understanding The problem provides a list of meeting intervals, where each interval is represented as [start, end] . Each pair describes the start time and end time of a meeting. The task is to determine whether a single person can attend every meeting without any scheduling conflicts. In simpler terms, we need to check whether any two meetings overlap...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 595 - Big Countries

LeetCode Problem 595 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to query a database table named World and return a subset of countries that qualify as big countries . Each row in the World table represents a country and contains five columns: Column Meaning name Country name continent Continent where the country belongs area Total land area in square kilometers population Number of people living...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 374 - Guess Number Higher or Lower

LeetCode Problem 374 Difficulty: 🟢 Easy Topics: Binary Search, Interactive Solution Problem Understanding The problem describes a classic interactive guessing game. A hidden number called pick is chosen somewhere in the range from 1 to n , inclusive. We are not allowed to access pick directly. Instead, we can only interact with the provided API function: guess(num) This API tells us whether our current guess is too high, too low,...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 717 - 1-bit and 2-bit Characters

LeetCode Problem 717 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding In this problem, we are given a binary array called bits . The array represents a sequence of encoded characters using the following rules: A one-bit character is represented by a single 0 A two-bit character is represented by either 10 or 11 The array is guaranteed to end with 0 . Our task is to determine whether the...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 860 - Lemonade Change

LeetCode Problem 860 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding This problem simulates a lemonade stand where each lemonade costs $5 . Customers come in a specific order and pay with a $5 , $10 , or $20 bill. The challenge is to provide exact change to every customer as they pay. The input is a list of integers bills , where each element represents the bill a...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 575 - Distribute Candies

LeetCode Problem 575 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding This problem asks us to maximize the number of distinct candy types Alice can eat while respecting a strict limit on how many candies she is allowed to consume. We are given an integer array candyType , where each element represents the type of a candy. Multiple candies may share the same type value. The total number...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1534 - Count Good Triplets

LeetCode Problem 1534 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding The problem asks us to count the number of good triplets in an integer array arr based on three difference constraints a , b , and c . A triplet (arr[i], arr[j], arr[k]) is considered good if it satisfies three conditions simultaneously: the indices i , j , and k are strictly increasing ( 0 <= i <...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 83 - Remove Duplicates from Sorted List

LeetCode Problem 83 Difficulty: 🟢 Easy Topics: Linked List Solution Problem Understanding This problem asks us to remove duplicate values from a sorted singly linked list so that every distinct value appears exactly once. The important detail is that the linked list is already sorted in ascending order, which makes duplicate detection much easier than in an unsorted list. The input is the head of a singly linked list. Each...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 485 - Max Consecutive Ones

LeetCode Problem 485 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us a binary array named nums , where every element is either 0 or 1 . Our task is to determine the maximum number of consecutive 1 s that appear anywhere in the array. In other words, we need to scan through the array and identify the longest uninterrupted sequence of 1 s. A sequence ends...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1331 - Rank Transform of an Array

LeetCode Problem 1331 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting Solution Problem Understanding The problem asks us to replace every number in the input array with its rank when the array is sorted in ascending order. A rank is defined by the relative ordering of the values: The smallest unique value gets rank 1 The second smallest unique value gets rank 2 Equal values must receive the same rank...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 521 - Longest Uncommon Subsequence I

LeetCode Problem 521 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to find the length of the longest uncommon subsequence between two strings a and b . To understand the problem clearly, we first need to understand what an uncommon subsequence means. A subsequence is a sequence of characters that can be obtained from a string by deleting zero or more characters without changing the relative...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1342 - Number of Steps to Reduce a Number to Zero

LeetCode Problem 1342 Difficulty: 🟢 Easy Topics: Math, Bit Manipulation Solution LeetCode 1342, Number of Steps to Reduce a Number to Zero Problem Understanding The problem gives us a non-negative integer num and asks us to compute how many operations are required to reduce it all the way down to 0 . At every step, we apply one of two rules: If the current number is even, divide it by...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 70 - Climbing Stairs

LeetCode Problem 70 Difficulty: 🟢 Easy Topics: Math, Dynamic Programming, Memoization Solution LeetCode 70 - Climbing Stairs Problem Understanding The problem describes a staircase with n total steps. You start at the bottom and want to reach the top. At every move, you are allowed to climb either 1 step or 2 steps. The goal is to determine how many distinct sequences of moves can take you from the bottom...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1848 - Minimum Distance to the Target Element

LeetCode Problem 1848 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us an integer array nums , a value called target , and an index called start . We need to find an index i where nums[i] == target and the distance between i and start is as small as possible. The distance is measured using the absolute difference: $|i-start|$ This means we only care about how...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 181 - Employees Earning More Than Their Managers

LeetCode Problem 181 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem gives us a single database table named Employee . Each row represents one employee and contains four pieces of information: Column Meaning id Unique identifier for the employee name Employee name salary Employee salary managerId The id of that employee's manager The goal is to return the names of employees whose salary is strictly greater than the...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 888 - Fair Candy Swap

LeetCode Problem 888 Difficulty: 🟢 Easy Topics: Array, Hash Table, Binary Search, Sorting Solution LeetCode 888 - Fair Candy Swap Problem Understanding The problem gives us two arrays, aliceSizes and bobSizes , representing the candy boxes owned by Alice and Bob. Each element in the arrays is the number of candies in a particular box. Alice and Bob want to exchange exactly one box each so that, after the swap,...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 461 - Hamming Distance

LeetCode Problem 461 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem asks us to compute the Hamming distance between two integers. The Hamming distance is defined as the number of bit positions where the two numbers differ in their binary representation. For example, consider x = 1 and y = 4 . Their binary representations are: 1 = 0001 4 = 0100 If we compare the bits...

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LeetCode 415 - Add Strings

LeetCode Problem 415 Difficulty: 🟢 Easy Topics: Math, String, Simulation Solution Problem Understanding The problem asks us to add two non-negative integers where each integer is given as a string instead of a numeric type. The goal is to return the resulting sum as another string. For example, if the inputs are "11" and "123" , we should return "134" . The important restriction is that we are not allowed...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 830 - Positions of Large Groups

LeetCode Problem 830 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to identify all large groups in a given string and return their positions as intervals. A group is a sequence of consecutive identical characters. For example, in the string abbxxxxzzy , the groups are: "a" "bb" "xxxx" "zz" "y" Each group can be represented by its starting index and ending index , inclusive. For example,...

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LeetCode 367 - Valid Perfect Square

LeetCode Problem 367 Difficulty: 🟢 Easy Topics: Math, Binary Search Solution Problem Understanding The problem asks us to determine whether a given positive integer num is a perfect square without using built in square root functions such as sqrt() . A perfect square is a number that can be written as: $n = k^2$ where k is an integer. For example, 16 is a perfect square because 4 * 4...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 661 - Image Smoother

LeetCode Problem 661 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Problem Understanding The problem is asking us to implement an image smoother , a filter that modifies each cell in a 2D grayscale image based on the average of itself and its surrounding cells in a 3 x 3 window. The key requirement is that we only consider the neighboring cells that exist; for edge or corner cells, the number...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 112 - Path Sum

LeetCode Problem 112 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to determine whether a binary tree contains at least one valid root-to-leaf path whose node values add up to a given target sum. A binary tree consists of nodes where each node can have a left child and a right child. Each node also stores an integer value. The...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 627 - Swap Sex of Employees

LeetCode Problem 627 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to swap the sex values of all employees in a Salary table. Each row in the table represents an employee with four columns: id , name , sex , and salary . The sex column is an ENUM with values 'm' for male and 'f' for female. The task is to flip these values...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 118 - Pascal's Triangle

LeetCode Problem 118 Difficulty: 🟢 Easy Topics: Array, Dynamic Programming Solution Problem Understanding The problem is asking us to generate the first numRows of Pascal's triangle , which is a triangular arrangement of numbers where each number is the sum of the two numbers directly above it. The first row is always [1] , the second row [1, 1] , and subsequent rows are built by summing pairs of adjacent...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1773 - Count Items Matching a Rule

LeetCode Problem 1773 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem asks us to determine how many items in a list satisfy a given rule. Each item is represented as a list of three strings: its type, color, and name. The rule is given as two strings: ruleKey and ruleValue . The ruleKey specifies which attribute of the item to compare ( type , color , or...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1051 - Height Checker

LeetCode Problem 1051 Difficulty: 🟢 Easy Topics: Array, Sorting, Counting Sort Solution Problem Understanding The problem gives us an array called heights , where each value represents the height of a student standing in a line. The school wants the students arranged in non-decreasing order, meaning heights should appear from smallest to largest, allowing duplicates. We are asked to determine how many students are currently standing in the wrong position...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1821 - Find Customers With Positive Revenue this Year

LeetCode Problem 1821 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Customers with three columns: Column Meaning customer_id Unique identifier for a customer year The year associated with the revenue revenue Revenue value for that customer in that year The combination (customer_id, year) is guaranteed to be unique, which means a customer can appear at most once for a given year. The...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1421 - NPV Queries

LeetCode Problem 1421 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem presents two database tables: NPV and Queries . The NPV table contains historical net present value (NPV) data for different inventory items identified by an id and a year . The Queries table contains requests for the NPV of specific inventory items at specific years. Each row in Queries represents a single query. The task is to...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1232 - Check If It Is a Straight Line

LeetCode Problem 1232 Difficulty: 🟢 Easy Topics: Array, Math, Geometry Solution Problem Understanding The problem asks us to determine whether a given set of points in a 2D Cartesian plane all lie on a single straight line. The input is a list of integer coordinates, where each coordinate [x, y] represents a point. The expected output is a boolean: true if all the points lie on a straight line, and...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 100 - Same Tree

LeetCode Problem 100 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether two binary trees are exactly the same. We are given the roots of two binary trees, p and q . A binary tree consists of nodes where each node contains a value and references to a left child and a right child. The task is to...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1295 - Find Numbers with Even Number of Digits

LeetCode Problem 1295 Difficulty: 🟢 Easy Topics: Array, Math Solution Problem Understanding The problem asks us to determine how many numbers in a given array nums have an even number of digits . The input is an array of integers, and the output is a single integer representing the count of numbers with an even digit length. For example, the number 12 has 2 digits, which is even, while 345...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 482 - License Key Formatting

LeetCode Problem 482 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string s that represents a license key. The string contains uppercase letters, lowercase letters, digits, and dashes. The existing dashes are only separators and do not necessarily represent the correct final grouping. We must reformat the string according to two rules: Every group after formatting must contain exactly k characters, except the first group....

Practice › LeetCode › LeetCode 05xx ›

LeetCode 504 - Base 7

LeetCode Problem 504 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to convert a given integer num into its representation in base 7, returning the result as a string. In other words, instead of representing the number in the usual decimal system (base 10), we represent it in a numeral system where each digit represents a power of 7, ranging from 0 to 6. For...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3028 - Ant on the Boundary

LeetCode Problem 3028 Difficulty: 🟢 Easy Topics: Array, Simulation, Prefix Sum Solution Problem Understanding The problem describes an ant moving along a one-dimensional infinite line, starting at a boundary point, which we can consider as position 0 . The ant reads through an array of non-zero integers, nums . Each integer represents a movement: positive numbers move the ant to the right and negative numbers move it to the left....

Practice › LeetCode › LeetCode 09xx ›

LeetCode 942 - DI String Match

LeetCode Problem 942 Difficulty: 🟢 Easy Topics: Array, Two Pointers, String, Greedy Solution Problem Understanding In this problem, we are given a string s consisting only of the characters 'I' and 'D' . The string has length n , and we must construct a permutation of the integers from 0 to n , inclusive. A permutation means every number in the range appears exactly once. Since the range is [0,...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1068 - Product Sales Analysis I

LeetCode Problem 1068 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to combine information from two database tables, Sales and Product , and produce a result containing the product name, the year of the sale, and the sale price for every sale record. The Sales table stores transactional information. Each row represents a product sale in a specific year. The table contains: sale_id , the identifier...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1587 - Bank Account Summary II

LeetCode Problem 1587 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to analyze banking transaction data and determine which users currently have a balance greater than 10000 . We are given two database tables: The Users table stores account information. Each row contains: account , the unique account number name , the user's name The Transactions table stores every transaction that affects an account. Each row...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1287 - Element Appearing More Than 25% In Sorted Array

LeetCode Problem 1287 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem gives us a sorted integer array in non-decreasing order. We are guaranteed that exactly one element appears more than 25% of the time in the array, and we need to return that element. In other words, among all numbers in the array, there is one value whose frequency is strictly greater than n / 4 , where...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 674 - Longest Continuous Increasing Subsequence

LeetCode Problem 674 Difficulty: 🟢 Easy Topics: Array Solution Problem Understanding The problem asks us to find the length of the longest strictly increasing contiguous segment in an array. The key detail is that the subsequence must be continuous, which means the elements must appear next to each other in the original array. Given an integer array nums , we need to determine the maximum length of any subarray where...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 303 - Range Sum Query - Immutable

LeetCode Problem 303 Difficulty: 🟢 Easy Topics: Array, Design, Prefix Sum Solution Problem Understanding The problem asks us to design a data structure that supports efficient range sum queries on a fixed array. We are given an integer array nums , and after initialization, the array never changes. The goal is to answer multiple queries of the form: What is the sum of all elements between index left and index...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 257 - Binary Tree Paths

LeetCode Problem 257 Difficulty: 🟢 Easy Topics: String, Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to return every path from the root of a binary tree to each leaf node. A root-to-leaf path is formed by starting at the root node and continuously moving downward through child nodes until reaching a node that has no children. The input is the root node of a...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1496 - Path Crossing

LeetCode Problem 1496 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding This problem asks us to simulate movement on a 2D plane according to a string of directional instructions. Each character in the string represents a move of one unit in a cardinal direction: 'N' for north (up), 'S' for south (down), 'E' for east (right), and 'W' for west (left). You always start at the origin (0,...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 682 - Baseball Game

LeetCode Problem 682 Difficulty: 🟢 Easy Topics: Array, Stack, Simulation Solution Problem Understanding This problem asks us to simulate a baseball scoring system with a set of unusual rules. We begin with an empty score record and process a sequence of operations one by one. Each operation either adds a new score or modifies the history of previously recorded scores. The input is an array of strings called operations ....

Practice › LeetCode › LeetCode 05xx ›

LeetCode 572 - Subtree of Another Tree

LeetCode Problem 572 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, String Matching, Binary Tree, Hash Function Solution LeetCode 572 - Subtree of Another Tree Problem Understanding This problem asks us to determine whether one binary tree appears as an exact subtree inside another binary tree. We are given two binary trees: root , the main tree subRoot , the candidate subtree We must return true if there exists some node...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1623 - All Valid Triplets That Can Represent a Country

LeetCode Problem 1623 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to generate all valid triplets of students representing a country from three schools: SchoolA , SchoolB , and SchoolC . Each triplet consists of one student from each school, and the triplet is only valid if all three students have distinct names and distinct IDs. The input consists of three database tables, each representing a...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1826 - Faulty Sensor

LeetCode Problem 1826 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding The problem gives us two arrays, sensor1 and sensor2 , representing readings collected simultaneously by two sensors. Under normal circumstances, both sensors should produce the same sequence of values. However, one sensor may be defective. A defective sensor behaves in a very specific way. It drops exactly one value somewhere in the sequence. After that dropped value,...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 586 - Customer Placing the Largest Number of Orders

LeetCode Problem 586 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Orders with two columns: Column Meaning order_number Unique identifier for an order customer_number Identifier for the customer who placed the order Each row represents a single order placed by a customer. A customer may appear multiple times because a customer can place multiple orders. The task is to determine which customer...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 938 - Range Sum of BST

LeetCode Problem 938 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root of a Binary Search Tree, abbreviated as BST, along with two integers, low and high . We must compute the sum of all node values whose values lie inside the inclusive range [low, high] . A Binary Search Tree has an important property: Every node in...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1731 - The Number of Employees Which Report to Each Employee

LeetCode Problem 1731 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The Employees table stores information about employees inside a company. Each row represents one employee and contains four columns: Column Meaning employee_id Unique identifier for the employee name Employee name reports_to The manager this employee reports to age Employee age If reports_to is NULL , that employee does not report to anyone. The problem defines a manager as any...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 125 - Valid Palindrome

LeetCode Problem 125 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding This problem asks us to determine whether a given string is a palindrome after applying two transformations: Convert all uppercase letters to lowercase. Remove all non-alphanumeric characters. An alphanumeric character is any English letter ( a-z , A-Z ) or digit ( 0-9 ). Characters such as spaces, punctuation marks, commas, colons, and symbols should be ignored...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 605 - Can Place Flowers

LeetCode Problem 605 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding The problem gives us a binary array called flowerbed , where: 0 represents an empty plot 1 represents a plot that already contains a flower We are also given an integer n , which represents how many new flowers we want to plant. The key restriction is that flowers cannot be planted in adjacent plots . This means...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1523 - Count Odd Numbers in an Interval Range

LeetCode Problem 1523 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem gives two non-negative integers, low and high , representing the inclusive bounds of an interval. We need to determine how many odd integers exist between these two values, including both endpoints. An integer is odd if it is not divisible by 2. Examples of odd numbers are 1 , 3 , 5 , and 7 . Examples...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 836 - Rectangle Overlap

LeetCode Problem 836 Difficulty: 🟢 Easy Topics: Math, Geometry Solution LeetCode 836, Rectangle Overlap Problem Understanding The problem gives us two axis-aligned rectangles , meaning their sides are parallel to the X-axis and Y-axis. Each rectangle is represented as: [x1, y1, x2, y2] Where: (x1, y1) is the bottom-left corner (x2, y2) is the top-right corner The task is to determine whether these two rectangles overlap with positive area ....

Practice › LeetCode › LeetCode 01xx ›

LeetCode 160 - Intersection of Two Linked Lists

LeetCode Problem 160 Difficulty: 🟢 Easy Topics: Hash Table, Linked List, Two Pointers Solution LeetCode 160, Intersection of Two Linked Lists Problem Understanding This problem asks us to determine whether two singly linked lists share a common node, and if they do, return the exact node where the intersection begins. The important detail is that an intersection is based on node reference, not node value. Two nodes containing the same...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1108 - Defanging an IP Address

LeetCode Problem 1108 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to transform a valid IPv4 address into its "defanged" version. A defanged IP address is created by replacing every period character "." with the string "[.]" . An IPv4 address consists of four numeric segments separated by periods. For example, "1.1.1.1" contains four numbers separated by three periods. The required transformation changes each separator so...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2224 - Minimum Number of Operations to Convert Time

LeetCode Problem 2224 Difficulty: 🟢 Easy Topics: String, Greedy Solution Problem Understanding The problem asks us to calculate the minimum number of operations to convert one 24-hour time string, current , into another, correct . Both inputs are formatted as "HH:MM" , where HH is hours from 00 to 23 and MM is minutes from 00 to 59 . Each operation allows us to increase the current time by 1,...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 69 - Sqrt(x)

LeetCode Problem 69 Difficulty: 🟢 Easy Topics: Math, Binary Search Solution Problem Understanding The problem asks us to compute the integer square root of a non negative integer x . More specifically, we need to return the largest integer k such that: $$k^2 \leq x$$ This means we are not looking for the exact decimal square root. Instead, we must round down to the nearest integer. For example, the square...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 266 - Palindrome Permutation

LeetCode Problem 266 Difficulty: 🟢 Easy Topics: Hash Table, String, Bit Manipulation Solution Problem Understanding The problem asks whether the characters of a given string can be rearranged to form a palindrome. A palindrome is a string that reads the same forward and backward. Examples include "racecar" , "abba" , and "a" . The important detail is that we are not asked to actually generate the palindrome. We only need...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 559 - Maximum Depth of N-ary Tree

LeetCode Problem 559 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search Solution Problem Understanding The problem asks us to compute the maximum depth of an n-ary tree. An n-ary tree is a tree where each node can have zero or more children, unlike a binary tree where each node has at most two children. The depth of a tree is defined as the number of nodes along the longest...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1207 - Unique Number of Occurrences

LeetCode Problem 1207 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 1207 - Unique Number of Occurrences Problem Understanding The problem gives us an integer array arr and asks whether every distinct number appears a unique number of times. In other words, we first count how many times each value occurs in the array. After we have all the frequencies, we must verify that no two different values share...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 448 - Find All Numbers Disappeared in an Array

LeetCode Problem 448 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem asks us to find all the integers in the range [1, n] that are missing from an input array nums of length n . Each element in nums is guaranteed to be an integer between 1 and n inclusive, but some numbers in this range may not appear in the array, and some numbers may...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 278 - First Bad Version

LeetCode Problem 278 Difficulty: 🟢 Easy Topics: Binary Search, Interactive Solution Problem Understanding The problem gives us a sequence of product versions numbered from 1 to n . At some point, one version becomes bad, and every version after it is also bad. This creates a monotonic pattern: Good versions appear first Bad versions appear afterward For example: Version: 1 2 3 4 5 Status : G G G B...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1700 - Number of Students Unable to Eat Lunch

LeetCode Problem 1700 Difficulty: 🟢 Easy Topics: Array, Stack, Queue, Simulation Solution Problem Understanding This problem simulates a school cafeteria where students line up to take sandwiches from a stack. Each student has a preference for either a circular sandwich ( 0 ) or a square sandwich ( 1 ). The sandwiches are arranged in a stack where the first element of the sandwiches array represents the top of the...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 144 - Binary Tree Preorder Traversal

LeetCode Problem 144 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Tree Solution LeetCode 144, Binary Tree Preorder Traversal Problem Understanding This problem asks us to return the preorder traversal of a binary tree. A binary tree consists of nodes where each node may have a left child and a right child. The input root represents the root node of that tree. In a preorder traversal, nodes are visited...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1662 - Check If Two String Arrays are Equivalent

LeetCode Problem 1662 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem gives us two arrays of strings, word1 and word2 . Each array represents a single larger string formed by concatenating all of its elements in order. Our task is to determine whether the final strings produced by both arrays are exactly the same. For example, if: word1 = ["ab", "c"] word2 = ["a", "bc"] then: word1...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 884 - Uncommon Words from Two Sentences

LeetCode Problem 884 Difficulty: 🟢 Easy Topics: Hash Table, String, Counting Solution LeetCode 884, Uncommon Words from Two Sentences Problem Understanding This problem asks us to find all words that are considered "uncommon" between two sentences. Each sentence is made up of lowercase words separated by single spaces. A word is considered uncommon if it satisfies two conditions: It appears exactly once in one sentence. It does not appear at...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1688 - Count of Matches in Tournament

LeetCode Problem 1688 Difficulty: 🟢 Easy Topics: Math, Simulation Solution Problem Understanding The problem describes a tournament where teams compete until only one winner remains. At every round, teams are paired to play matches, but the tournament follows slightly unusual rules depending on whether the current number of teams is even or odd. If the number of teams is even, every team gets paired with another team. Since each match...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1694 - Reformat Phone Number

LeetCode Problem 1694 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem requires reformatting a phone number string in a specific structured way. The input is a string number containing digits, spaces, and dashes. Our task is to first remove all non-digit characters, then partition the digits into blocks of length 3, with special handling for the last few digits: if exactly 4 digits remain, split them into two...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1517 - Find Users With Valid E-Mails

LeetCode Problem 1517 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to query a database table named Users and return only the rows corresponding to users whose e-mail addresses are considered valid according to a very specific format. Each row in the Users table contains three columns: user_id , a unique integer identifier for each user name , the user's name mail , the user's e-mail...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 506 - Relative Ranks

LeetCode Problem 506 Difficulty: 🟢 Easy Topics: Array, Sorting, Heap (Priority Queue) Solution LeetCode 506 - Relative Ranks Problem Understanding The problem gives us an array named score , where each element represents the score earned by an athlete in a competition. Every athlete has a unique score, which means there are no ties to worry about when determining rankings. We need to determine each athlete's placement based on score...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1137 - N-th Tribonacci Number

LeetCode Problem 1137 Difficulty: 🟢 Easy Topics: Math, Dynamic Programming, Memoization Solution LeetCode 1137, N-th Tribonacci Number Problem Understanding The problem asks us to compute the n -th number in the Tribonacci sequence. The Tribonacci sequence is very similar to the Fibonacci sequence, except that instead of summing the previous two numbers, each value is formed by summing the previous three numbers. The sequence is defined as: T0 = 0...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 557 - Reverse Words in a String III

LeetCode Problem 557 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem requires reversing the characters of each individual word in a string while maintaining the original order of the words and the spacing between them. In other words, the sentence structure remains the same, but each word is mirrored in place. For example, the word "Let's" becomes "s'teL" , and "LeetCode" becomes "edoCteeL" . The input...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1309 - Decrypt String from Alphabet to Integer Mapping

LeetCode Problem 1309 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem gives us a string containing digits and the '#' character. This string encodes lowercase English letters using a special mapping rule. The mapping works in two different ways: Digits '1' through '9' represent the letters 'a' through 'i' Two digit numbers followed by '#' , from "10#" through "26#" , represent the letters 'j' through 'z' Our...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 27 - Remove Element

LeetCode Problem 27 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Problem Understanding The problem gives us an integer array nums and a target value val . Our task is to remove every occurrence of val from the array, but we must do it in-place. This means we are not supposed to create another array and return it. Instead, we modify the original array directly. The function should return an...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1180 - Count Substrings with Only One Distinct Letter

LeetCode Problem 1180 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to count how many substrings of a given string contain only one distinct character. A substring is a contiguous section of the string. For example, in the string "aaaba" , the substring "aaa" is valid because every character is 'a' . The substring "aab" is not valid because it contains both 'a' and 'b'...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1427 - Perform String Shifts

LeetCode Problem 1427 Difficulty: 🟢 Easy Topics: Array, Math, String Solution Problem Understanding This problem asks us to simulate a sequence of string shift operations on a given string s . Each operation in the shift matrix contains two values: direction 0 means shift left 1 means shift right amount the number of positions to shift A left shift removes characters from the front and appends them to the back....

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1134 - Armstrong Number

LeetCode Problem 1134 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding In this problem, we are given an integer n , and we must determine whether it is an Armstrong number. An Armstrong number is defined as follows: Let k be the number of digits in n . Take every digit in the number. Raise each digit to the power k . Sum all those powered values. If the final...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1050 - Actors and Directors Who Cooperated At Least Three Times

LeetCode Problem 1050 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify every (actor_id, director_id) pair where an actor and a director have collaborated at least three times. The input is a database table named ActorDirector . Each row represents one collaboration event between an actor and a director. The table contains three columns: actor_id , which uniquely identifies an actor director_id , which uniquely...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1399 - Count Largest Group

LeetCode Problem 1399 Difficulty: 🟢 Easy Topics: Hash Table, Math, Counting Solution Problem Understanding The problem asks us to group all integers from 1 to n based on the sum of their digits. Every number belongs to exactly one group, determined by adding together all of its decimal digits. For example: 14 has digit sum 1 + 4 = 5 5 also has digit sum 5 So both numbers belong...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1013 - Partition Array Into Three Parts With Equal Sum

LeetCode Problem 1013 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding The problem gives us an integer array arr and asks whether it can be divided into exactly three non-empty contiguous parts such that all three parts have the same sum. The partitions must preserve the original order of the array. We are not allowed to rearrange elements. Instead, we choose two cut positions that split the array into:...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 476 - Number Complement

LeetCode Problem 476 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem asks us to compute the complement of a positive integer by flipping every bit in its binary representation. A binary complement means changing every 1 bit into 0 , and every 0 bit into 1 . For example, the integer 5 is represented in binary as 101 . Flipping each bit gives 010 , which is...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 344 - Reverse String

LeetCode Problem 344 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem asks us to reverse a string that is represented as an array of characters. Instead of returning a new reversed string, we must modify the original array directly. This requirement is important because the problem explicitly states that the solution must work in-place and use only O(1) extra memory. The input is an array s...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1768 - Merge Strings Alternately

LeetCode Problem 1768 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding The problem requires merging two input strings word1 and word2 in an alternating fashion, starting with the first character of word1 . This means we take one character from word1 , then one character from word2 , and repeat this process until one or both strings are exhausted. If one string is longer than the other, the...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1365 - How Many Numbers Are Smaller Than the Current Number

LeetCode Problem 1365 Difficulty: 🟢 Easy Topics: Array, Hash Table, Sorting, Counting Sort Solution Problem Understanding The problem asks us to determine, for each element in an array, how many elements in the same array are strictly smaller than it. In other words, for an element nums[i] , we count all elements nums[j] such that nums[j] < nums[i] and j != i . The input is a list of integers...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 748 - Shortest Completing Word

LeetCode Problem 748 Difficulty: 🟢 Easy Topics: Array, Hash Table, String Solution Problem Understanding The problem gives us a string called licensePlate and an array of candidate words called words . We must find the shortest word that satisfies all the letter requirements contained in licensePlate . The key detail is that only alphabetic characters matter. Digits and spaces should be ignored completely. In addition, uppercase and lowercase letters are...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 868 - Binary Gap

LeetCode Problem 868 Difficulty: 🟢 Easy Topics: Bit Manipulation Solution Problem Understanding The problem asks us to examine the binary representation of a positive integer n and determine the largest distance between two adjacent 1 bits. A binary number is made up of 0 s and 1 s. For example: 22 in binary is 10110 5 in binary is 101 8 in binary is 1000 We are interested only in...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1271 - Hexspeak

LeetCode Problem 1271 Difficulty: 🟢 Easy Topics: Math, String Solution Problem Understanding The problem asks us to convert a decimal number given as a string into its Hexspeak representation. Hexspeak is derived from the hexadecimal representation of the number, with a simple character substitution: '0' becomes 'O' and '1' becomes 'I' . A valid Hexspeak string can only contain the characters {'A', 'B', 'C', 'D', 'E', 'F', 'I', 'O'} ....

Practice › LeetCode › LeetCode 03xx ›

LeetCode 338 - Counting Bits

LeetCode Problem 338 Difficulty: 🟢 Easy Topics: Dynamic Programming, Bit Manipulation Solution Problem Understanding The problem asks us to compute the number of set bits, also called population count or popcount, for every integer from 0 through n . A set bit is a bit with value 1 in the binary representation of a number. For example: 5 in binary is 101 , which contains two 1 bits 7 in...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 121 - Best Time to Buy and Sell Stock

LeetCode Problem 121 Difficulty: 🟢 Easy Topics: Array, Dynamic Programming Solution Problem Understanding This problem asks us to determine the maximum profit that can be made from a single stock transaction . A transaction consists of buying one stock on one day and selling it on a later day. The key restriction is that the selling day must come after the buying day. The input is an integer array prices...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1720 - Decode XORed Array

LeetCode Problem 1720 Difficulty: 🟢 Easy Topics: Array, Bit Manipulation Solution Problem Understanding The problem gives us an encoded array where each element represents the XOR of two consecutive elements from an unknown original array. Specifically: encoded[i] = arr[i] XOR arr[i + 1] We are also given the first element of the original array, first = arr[0] . Using these two pieces of information, we must reconstruct the entire original...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 26 - Remove Duplicates from Sorted Array

LeetCode Problem 26 Difficulty: 🟢 Easy Topics: Array, Two Pointers Solution Remove Duplicates from Sorted Array Problem Understanding The problem gives us a sorted integer array nums in non-decreasing order. Because the array is already sorted, any duplicate values will always appear next to each other. Our task is to remove duplicate values in-place so that each distinct number appears exactly once at the beginning of the array. The phrase...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 961 - N-Repeated Element in Size 2N Array

LeetCode Problem 961 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution Problem Understanding The problem gives us an integer array nums whose length is exactly 2 * n . Among all the numbers in the array, there are n + 1 distinct values. One special value appears exactly n times, while every other value appears only once. Our task is to identify and return the value that appears repeatedly. Another...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1678 - Goal Parser Interpretation

LeetCode Problem 1678 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding This problem asks us to interpret a Goal Parser command string . The string command consists of the characters "G" , "()" , and "(al)" in some order. Each symbol has a specific interpretation: "G" is interpreted as "G" , "()" is interpreted as "o" , and "(al)" is interpreted as "al" . The final result is the concatenation...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1185 - Day of the Week

LeetCode Problem 1185 Difficulty: 🟢 Easy Topics: Math Solution LeetCode 1185 - Day of the Week Problem Understanding This problem asks us to determine which day of the week corresponds to a given calendar date. The input consists of three integers: day , representing the day within the month month , representing the month number from 1 to 12 year , representing the year We must return the correct weekday...

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LeetCode 1211 - Queries Quality and Percentage

LeetCode Problem 1211 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Queries . Each row represents the outcome of running a particular query against a database. The columns are: Column Meaning query_name The name of the query group result The returned result string position The rank or position of the result rating A score from 1 to 5 evaluating the result quality...

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LeetCode 563 - Binary Tree Tilt

LeetCode Problem 563 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to compute the total tilt of an entire binary tree. Every node in the tree has its own tilt, and the final answer is the sum of all individual node tilts. The tilt of a node is defined as the absolute difference between: The sum of all values in its left...

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LeetCode 597 - Friend Requests I: Overall Acceptance Rate

LeetCode Problem 597 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the overall acceptance rate of friend requests in a social network system. Two database tables are provided. The first table, FriendRequest , stores all friend requests that users sent to each other. The second table, RequestAccepted , stores requests that were accepted. The acceptance rate is defined as: $\text{Acceptance Rate} = \frac{\text{Number of...

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LeetCode 1816 - Truncate Sentence

LeetCode Problem 1816 Difficulty: 🟢 Easy Topics: Array, String Solution Problem Understanding The problem gives us a sentence s and an integer k . A sentence is guaranteed to contain words separated by exactly one space, with no extra spaces at the beginning or end. Our task is to return a new sentence that contains only the first k words from the original sentence. In other words, we need to...

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LeetCode 1582 - Special Positions in a Binary Matrix

LeetCode Problem 1582 Difficulty: 🟢 Easy Topics: Array, Matrix Solution Here is a complete, detailed technical solution guide for LeetCode 1582 - Special Positions in a Binary Matrix , following your formatting and content requirements precisely. Problem Understanding The problem provides an m x n binary matrix mat consisting only of 0 s and 1 s, and asks us to find the number of special positions . A position (i,...

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LeetCode 610 - Triangle Judgement

LeetCode Problem 610 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to determine, for each row in a table called Triangle , whether the three given line segments can form a valid triangle. Each row contains three integers x , y , and z representing the lengths of the segments. The expected output is a new table that includes all original columns plus a triangle...

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LeetCode 463 - Island Perimeter

LeetCode Problem 463 Difficulty: 🟢 Easy Topics: Array, Depth-First Search, Breadth-First Search, Matrix Solution Problem Understanding The problem asks us to calculate the perimeter of an island represented in a 2D grid. Each cell in the grid is either land ( 1 ) or water ( 0 ). The island consists of one or more connected land cells, where connectivity is strictly horizontal or vertical. The grid is completely surrounded...

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LeetCode 1469 - Find All The Lonely Nodes

LeetCode Problem 1469 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to traverse a binary tree and identify every node that is considered "lonely". A node is lonely if it is the only child of its parent. In other words, if a parent node has exactly one child, that child is lonely. The input is the root of a binary...

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LeetCode 700 - Search in a Binary Search Tree

LeetCode Problem 700 Difficulty: 🟢 Easy Topics: Tree, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root node of a Binary Search Tree, commonly abbreviated as a BST, along with an integer value val . Our goal is to locate the node whose value is exactly equal to val and return that node. Since the problem asks us to return the subtree rooted at that...

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LeetCode 1668 - Maximum Repeating Substring

LeetCode Problem 1668 Difficulty: 🟢 Easy Topics: String, Dynamic Programming, String Matching Solution Problem Understanding This problem asks us to determine how many times a given string word can be repeated consecutively while still appearing as a substring inside another string called sequence . More formally, a string is considered k-repeating if word concatenated k times appears somewhere inside sequence as a contiguous substring. Our goal is to find the...

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LeetCode 620 - Not Boring Movies

LeetCode Problem 620 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to query a database table called Cinema and return a filtered set of movies based on two conditions: the movie ID must be odd, and its description must not be "boring" . The result must then be sorted in descending order by the movie's rating . In other words, for every row in the...

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LeetCode 1260 - Shift 2D Grid

LeetCode Problem 1260 Difficulty: 🟢 Easy Topics: Array, Matrix, Simulation Solution LeetCode 1260 - Shift 2D Grid Problem Understanding This problem asks us to simulate repeated shift operations on a 2D matrix. We are given an m x n grid and an integer k , representing how many times the shift operation must be applied. A single shift operation moves every element one position forward in row-major order. This means:...

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LeetCode 1544 - Make The String Great

LeetCode Problem 1544 Difficulty: 🟢 Easy Topics: String, Stack Solution Problem Understanding The problem asks us to process a string s consisting of lowercase and uppercase English letters, removing pairs of adjacent letters that are the same character but differ in case. Specifically, any pair where one character is lowercase and the adjacent character is its uppercase counterpart (or vice versa) is considered "bad." We must remove such pairs iteratively...

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LeetCode 346 - Moving Average from Data Stream

LeetCode Problem 346 Difficulty: 🟢 Easy Topics: Array, Design, Queue, Data Stream Solution Problem Understanding The problem asks us to design a data structure that continuously receives integers from a stream and returns the average of the most recent values within a fixed-size sliding window. A sliding window means that we only care about the latest size elements. As new values arrive, older values eventually fall out of the window...

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LeetCode 434 - Number of Segments in a String

LeetCode Problem 434 Difficulty: 🟢 Easy Topics: String Solution Problem Understanding The problem asks us to count how many separate word-like groups exist inside a string. In this problem, a "segment" is defined as a continuous sequence of characters that are not spaces. Every time we encounter a block of non-space characters separated by spaces, that block counts as one segment. For example, in the string "Hello, my name is...

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LeetCode 1704 - Determine if String Halves Are Alike

LeetCode Problem 1704 Difficulty: 🟢 Easy Topics: String, Counting Solution Determine if String Halves Are Alike Problem Understanding The problem gives us a string s whose length is guaranteed to be even. We split the string into two equal parts: The first half is called a The second half is called b We must determine whether both halves contain the same number of vowels. The vowels include both lowercase and...

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LeetCode 997 - Find the Town Judge

LeetCode Problem 997 Difficulty: 🟢 Easy Topics: Array, Hash Table, Graph Theory Solution Problem Understanding The problem describes a town containing n people labeled from 1 to n . Among these people, there may exist a special person called the town judge. The judge must satisfy two strict conditions: The judge trusts nobody. Every other person trusts the judge. Additionally, the problem guarantees that if such a person exists, there...

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LeetCode 408 - Valid Word Abbreviation

LeetCode Problem 408 Difficulty: 🟢 Easy Topics: Two Pointers, String Solution Problem Understanding In this problem, we are given two strings: word , the original full word abbr , a supposed abbreviation of that word We must determine whether abbr is a valid abbreviation of word . An abbreviation works by replacing one or more non-empty substrings with their lengths. For example, "internationalization" can become "i12iz4n" because: "i" stays the...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 270 - Closest Binary Search Tree Value

LeetCode Problem 270 Difficulty: 🟢 Easy Topics: Binary Search, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the root of a Binary Search Tree, abbreviated as BST, and a floating point target value. Our task is to return the integer value stored in the BST that is numerically closest to the target. A Binary Search Tree has a very important property: Every node...

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LeetCode 1827 - Minimum Operations to Make the Array Increasing

LeetCode Problem 1827 Difficulty: 🟢 Easy Topics: Array, Greedy Solution Problem Understanding The problem asks us to transform a given integer array nums into a strictly increasing array using the minimum number of operations. An operation consists of incrementing any element of the array by 1 . A strictly increasing array is one where each element is strictly less than the next element, i.e., nums[i] < nums[i+1] for all valid...

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LeetCode 1021 - Remove Outermost Parentheses

LeetCode Problem 1021 Difficulty: 🟢 Easy Topics: String, Stack Solution Unusual activity has been detected from your device. Try again later. (36c3723c-3fa3-4b63-a514-20d2635d5e47)

Practice › LeetCode › LeetCode 01xx ›

LeetCode 196 - Delete Duplicate Emails

LeetCode Problem 196 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Person with two columns: id int email varchar The id column is unique because it is the primary key. The email column may contain duplicate values, meaning multiple rows can share the same email address. The task is to delete duplicate email rows while keeping exactly one row for each unique email...

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LeetCode 191 - Number of 1 Bits

LeetCode Problem 191 Difficulty: 🟢 Easy Topics: Divide and Conquer, Bit Manipulation Solution Problem Understanding The problem asks us to count how many bits are set to 1 in the binary representation of a positive integer n . A set bit is simply a bit whose value is 1 . For example, the number 11 in binary is: 1011 This binary representation contains three 1 bits, so the answer is...

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LeetCode 9 - Palindrome Number

LeetCode Problem 9 Difficulty: 🟢 Easy Topics: Math Solution Problem Understanding The problem asks us to determine whether a given integer reads the same forward and backward. Such numbers are called palindromes. For example, the number 121 is a palindrome because reversing its digits still produces 121 . On the other hand, 123 is not a palindrome because reversing it produces 321 . The input consists of a single integer...

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LeetCode 197 - Rising Temperature

LeetCode Problem 197 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Weather that stores daily temperature records. Each row contains three fields: a unique id , a recordDate , and the temperature recorded on that date. The task is to find all rows where the temperature is higher than the temperature recorded on the previous calendar day. In other words, for each...

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LeetCode 190 - Reverse Bits

LeetCode Problem 190 Difficulty: 🟢 Easy Topics: Divide and Conquer, Bit Manipulation Solution Problem Understanding The problem asks us to reverse the binary representation of a 32-bit integer . Instead of reversing the decimal digits of a number, we reverse the order of its individual bits. For example, suppose the binary representation of a number is: 00000010100101000001111010011100 After reversing all 32 bits, it becomes: 00111001011110000010100101000000 The resulting reversed binary value...

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LeetCode 193 - Valid Phone Numbers

LeetCode Problem 193 Difficulty: 🟢 Easy Topics: Shell Solution Problem Understanding This problem asks us to process a text file named file.txt and print only the phone numbers that match one of two valid formats. The valid formats are: xxx-xxx-xxxx and (xxx) xxx-xxxx In both formats, every x represents a single digit from 0 to 9 . The task is not to transform the input or extract partial matches. Instead,...

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LeetCode 202 - Happy Number

LeetCode Problem 202 Difficulty: 🟢 Easy Topics: Hash Table, Math, Two Pointers Solution Problem Understanding This problem asks us to determine whether a given positive integer n is a happy number . A happy number is defined through a repeated transformation process. Starting with the original number, we repeatedly replace it with the sum of the squares of its digits . Eventually, one of two things happens: The number becomes...

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LeetCode 195 - Tenth Line

LeetCode Problem 195 Difficulty: 🟢 Easy Topics: Shell Solution Problem Understanding This problem asks us to print exactly the 10th line from a text file named file.txt . The file contains multiple lines of plain text, and each line is separated by a newline character. The input is not provided as function arguments like many algorithm problems. Instead, the solution must work directly with a file in a shell scripting...

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LeetCode 1 - Two Sum

LeetCode Problem 1 Difficulty: 🟢 Easy Topics: Array, Hash Table Solution LeetCode 1, Two Sum Problem Understanding The problem gives us an integer array called nums and another integer called target . Our task is to find two different elements in the array whose sum equals target , then return their indices. The important detail is that the output must contain indices, not the values themselves. For example, if the...

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LeetCode 205 - Isomorphic Strings

LeetCode Problem 205 Difficulty: 🟢 Easy Topics: Hash Table, String Solution Problem Understanding The problem asks us to determine whether two strings, s and t , are isomorphic . Two strings are considered isomorphic if there exists a one-to-one mapping between characters in s and characters in t such that replacing every character in s according to this mapping produces t . In simpler terms, each character in s must...

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LeetCode 206 - Reverse Linked List

LeetCode Problem 206 Difficulty: 🟢 Easy Topics: Linked List, Recursion Solution Problem Understanding The problem asks us to reverse a singly linked list. A singly linked list is a sequence of nodes where each node stores a value and a pointer to the next node in the sequence. The input, head , represents the first node of the linked list. Our task is to rearrange the connections between the nodes...

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LeetCode 13 - Roman to Integer

LeetCode Problem 13 Difficulty: 🟢 Easy Topics: Hash Table, Math, String Solution Problem Understanding The problem gives a Roman numeral string and asks us to convert it into its corresponding integer value. Roman numerals use seven symbols: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Most Roman numerals follow a simple additive rule. Symbols are written from largest to smallest, and we...

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LeetCode 203 - Remove Linked List Elements

LeetCode Problem 203 Difficulty: 🟢 Easy Topics: Linked List, Recursion Solution Problem Understanding The problem asks us to remove every node from a singly linked list whose value is equal to a given integer val . After all matching nodes are removed, we must return the head of the modified linked list. A linked list is a linear data structure where each node stores a value and a reference to...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 145: Binary Tree Postorder Traversal

Problem Restatement We are given the root of a binary tree. Return the postorder traversal of its node values. Postorder traversal visits nodes in this order: left subtree -> right subtree -> root If the tree is empty, return an empty list. LeetCode also includes a follow-up asking for an iterative solution. Examples Example 1: 1 \ 2 / 3 Traversal order: visit left of 1: none visit right subtree...

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LeetCode 144: Binary Tree Preorder Traversal

Problem Restatement We are given the root of a binary tree. Return the preorder traversal of its node values. Preorder traversal visits nodes in this order: root -> left subtree -> right subtree The tree may be empty. In that case, return an empty list. LeetCode also includes a follow-up asking for an iterative solution. Examples Example 1: 1 \ 2 / 3 Preorder traversal: visit 1 go right to...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 141: Linked List Cycle

Problem Restatement We are given the head of a linked list. Return True if the linked list contains a cycle. Otherwise, return False . A cycle exists if some node can be reached again by continuously following next pointers. LeetCode internally represents the cycle using an index pos , where the tail node points back to the node at position pos . This value is not passed to the function....

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 136: Single Number

Problem Restatement We are given a non-empty integer array nums . Every element appears exactly twice except for one element. We need to return the element that appears only once. The solution must run in linear time and use constant extra space. LeetCode states this explicitly in the problem requirements. Examples Example 1: nums = [2, 2, 1] The number 2 appears twice. The number 1 appears once. Output: 1...

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LeetCode 3158 - Find the XOR of Numbers Which Appear Twice

LeetCode 3774 - Absolute Difference Between Maximum and Minimum K Elements

LeetCode 3438 - Find Valid Pair of Adjacent Digits in String

LeetCode 3633 - Earliest Finish Time for Land and Water Rides I

LeetCode 3637 - Trionic Array I

LeetCode 3602 - Hexadecimal and Hexatrigesimal Conversion

LeetCode 3875 - Construct Uniform Parity Array I

LeetCode 3884 - First Matching Character From Both Ends

LeetCode 3880 - Minimum Absolute Difference Between Two Values

LeetCode 3870 - Count Commas in Range

LeetCode 3866 - First Unique Even Element

LeetCode 3769 - Sort Integers by Binary Reflection

LeetCode 3856 - Trim Trailing Vowels

LeetCode 3852 - Smallest Pair With Different Frequencies

LeetCode 3754 - Concatenate Non-Zero Digits and Multiply by Sum I

LeetCode 3750 - Minimum Number of Flips to Reverse Binary String

LeetCode 3842 - Toggle Light Bulbs

LeetCode 3838 - Weighted Word Mapping

LeetCode 3833 - Count Dominant Indices

LeetCode 3803 - Count Residue Prefixes

LeetCode 3827 - Count Monobit Integers

LeetCode 3736 - Minimum Moves to Equal Array Elements III

LeetCode 3823 - Reverse Letters Then Special Characters in a String

LeetCode 3731 - Find Missing Elements

LeetCode 3813 - Vowel-Consonant Score

LeetCode 3712 - Sum of Elements With Frequency Divisible by K

LeetCode 3696 - Maximum Distance Between Unequal Words in Array I

LeetCode 3692 - Majority Frequency Characters

LeetCode 3794 - Reverse String Prefix

LeetCode 3718 - Smallest Missing Multiple of K

LeetCode 3550 - Smallest Index With Digit Sum Equal to Index

LeetCode 3502 - Minimum Cost to Reach Every Position

LeetCode 3402 - Minimum Operations to Make Columns Strictly Increasing

LeetCode 3745 - Maximize Expression of Three Elements

LeetCode 3726 - Remove Zeros in Decimal Representation

LeetCode 3707 - Equal Score Substrings

LeetCode 3697 - Compute Decimal Representation

LeetCode 3688 - Bitwise OR of Even Numbers in an Array

LeetCode 3683 - Earliest Time to Finish One Task

LeetCode 3684 - Maximize Sum of At Most K Distinct Elements

LeetCode 3674 - Minimum Operations to Equalize Array

LeetCode 3667 - Sort Array By Absolute Value

LeetCode 3668 - Restore Finishing Order

LeetCode 3662 - Filter Characters by Frequency

LeetCode 3663 - Find The Least Frequent Digit

LeetCode 3658 - GCD of Odd and Even Sums

LeetCode 3643 - Flip Square Submatrix Vertically

LeetCode 3622 - Check Divisibility by Digit Sum and Product

LeetCode 3606 - Coupon Code Validator

LeetCode 3415 - Find Products with Three Consecutive Digits

LeetCode 3591 - Check if Any Element Has Prime Frequency

LeetCode 3582 - Generate Tag for Video Caption

LeetCode 3571 - Find the Shortest Superstring II

LeetCode 3570 - Find Books with No Available Copies

LeetCode 3560 - Find Minimum Log Transportation Cost

LeetCode 3545 - Minimum Deletions for At Most K Distinct Characters

LeetCode 3541 - Find Most Frequent Vowel and Consonant

LeetCode 3536 - Maximum Product of Two Digits

LeetCode 3516 - Find Closest Person

LeetCode 3512 - Minimum Operations to Make Array Sum Divisible by K

LeetCode 3507 - Minimum Pair Removal to Sort Array I

LeetCode 3498 - Reverse Degree of a String

LeetCode 3492 - Maximum Containers on a Ship

LeetCode 3491 - Phone Number Prefix

LeetCode 3477 - Fruits Into Baskets II

LeetCode 3471 - Find the Largest Almost Missing Integer

LeetCode 3461 - Check If Digits Are Equal in String After Operations I

LeetCode 3467 - Transform Array by Parity

LeetCode 3465 - Find Products with Valid Serial Numbers

LeetCode 3456 - Find Special Substring of Length K

LeetCode 3450 - Maximum Students on a Single Bench

LeetCode 3452 - Sum of Good Numbers

LeetCode 3442 - Maximum Difference Between Even and Odd Frequency I

LeetCode 3436 - Find Valid Emails

LeetCode 3427 - Sum of Variable Length Subarrays

LeetCode 3423 - Maximum Difference Between Adjacent Elements in a Circular Array

LeetCode 3417 - Zigzag Grid Traversal With Skip

LeetCode 3411 - Maximum Subarray With Equal Products

LeetCode 3407 - Substring Matching Pattern