simulation | brain

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3616 - Number of Student Replacements

LeetCode Problem 3616 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding The problem models a simple selection process among students arriving one by one. Each student has a rank, where a smaller rank value represents a better student. The first arriving student is automatically selected. As additional students arrive, we compare their rank against the rank of the currently selected student. If the new student has a strictly better...

Practice › LeetCode › LeetCode 37xx ›

LeetCode 3792 - Sum of Increasing Product Blocks

LeetCode Problem 3792 Difficulty: 🟡 Medium Topics: Math, Simulation Solution Problem Understanding The problem defines a sequence of blocks, where each block contains the product of a consecutive range of integers. The pattern works as follows: The 1st block contains only 1 The 2nd block contains 2 × 3 The 3rd block contains 4 × 5 × 6 The 4th block contains 7 × 8 × 9 × 10 Notice...

Practice › LeetCode › LeetCode 38xx ›

LeetCode 3867 - Sum of GCD of Formed Pairs

LeetCode Problem 3867 Difficulty: 🟡 Medium Topics: Array, Math, Two Pointers, Simulation, Number Theory Solution LeetCode 3867 - Sum of GCD of Formed Pairs Problem Understanding We are given an integer array nums of length n . For every index i , we first compute: mxi , the maximum value among nums[0...i] prefixGcd[i] = gcd(nums[i], mxi) This creates a new array called prefixGcd . After that, we sort prefixGcd in...

Practice › LeetCode › LeetCode 37xx ›

LeetCode 3775 - Reverse Words With Same Vowel Count

LeetCode Problem 3775 Difficulty: 🟡 Medium Topics: Two Pointers, String, Simulation Solution Problem Understanding The problem requires processing a string s consisting of lowercase English words separated by single spaces. The first task is to count the number of vowels in the first word . Then, for each subsequent word in the string, if the word has the same number of vowels as the first word, it should be reversed....

Practice › LeetCode › LeetCode 38xx ›

LeetCode 3847 - Find the Score Difference in a Game

LeetCode Problem 3847 Difficulty: 🟡 Medium Topics: Array, Simulation Solution LeetCode 3847 - Find the Score Difference in a Game Problem Understanding This problem describes a game played over a sequence of rounds. The array nums represents the points awarded in each game, where nums[i] is the number of points available during game i . There are exactly two players. At the beginning: The first player is active. The second...

Practice › LeetCode › LeetCode 38xx ›

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...

Practice › LeetCode › LeetCode 38xx ›

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...

Practice › LeetCode › LeetCode 38xx ›

LeetCode 3834 - Merge Adjacent Equal Elements

LeetCode Problem 3834 Difficulty: 🟡 Medium Topics: Array, Stack, Simulation Solution Problem Understanding The problem asks us to repeatedly merge adjacent equal elements in an integer array nums until no further merges are possible. Specifically, if two consecutive elements are equal, we replace them with their sum. The key points are that we always pick the leftmost pair for merging, and after each merge, the array size decreases by one....

Practice › LeetCode › LeetCode 38xx ›

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...

Practice › LeetCode › LeetCode 38xx ›

LeetCode 3819 - Rotate Non Negative Elements

LeetCode Problem 3819 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding The problem asks us to rotate only the non-negative elements of an integer array nums to the left by k positions in a cyclic manner, while leaving all negative elements fixed in their original positions. In other words, the negative numbers act as "anchors" in the array, and the rotation affects only the positive numbers and zeros. After...

Practice › LeetCode › LeetCode 38xx ›

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...

Practice › LeetCode › LeetCode 37xx ›

LeetCode 3703 - Remove K-Balanced Substrings

LeetCode Problem 3703 Difficulty: 🟡 Medium Topics: String, Stack, Simulation Solution LeetCode 3703 - Remove K-Balanced Substrings Problem Understanding We are given a string s consisting only of '(' and ')' , along with an integer k . A substring is considered k-balanced if it is exactly: "(" repeated k times + ")" repeated k times For example: k = 1 → "()" k = 2 → "(())" k =...

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3679 - Minimum Discards to Balance Inventory

LeetCode Problem 3679 Difficulty: 🟡 Medium Topics: Array, Hash Table, Sliding Window, Simulation, Counting Solution LeetCode 3679 - Minimum Discards to Balance Inventory Problem Understanding This problem models a stream of arriving items. On each day, exactly one item arrives, and each item has a type represented by an integer. We are given two parameters: w , the size of the sliding window. m , the maximum number of times...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3522 - Calculate Score After Performing Instructions

LeetCode Problem 3522 Difficulty: 🟡 Medium Topics: Array, Hash Table, String, Simulation Solution Problem Understanding The problem presents a simulated execution environment defined by two parallel arrays, instructions and values , each of length n . Each index i represents a single instruction. The instructions[i] element can either be "add" or "jump" . If the instruction is "add" , the associated values[i] is added to a running score , and...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3412 - Find Mirror Score of a String

LeetCode Problem 3412 Difficulty: 🟡 Medium Topics: Hash Table, String, Stack, Simulation Solution LeetCode 3412 - Find Mirror Score of a String Problem Understanding We are given a lowercase English string s . Every letter has a unique "mirror" letter obtained by reversing the alphabet. For example: 'a' ↔ 'z' 'b' ↔ 'y' 'c' ↔ 'x' and so on. We process the string from left to right. For each position...

Practice › LeetCode › LeetCode 37xx ›

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....

Practice › LeetCode › LeetCode 36xx ›

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...

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3653 - XOR After Range Multiplication Queries I

LeetCode Problem 3653 Difficulty: 🟡 Medium Topics: Array, Divide and Conquer, Simulation Solution LeetCode 3653 - XOR After Range Multiplication Queries I Problem Understanding We are given an integer array nums and a list of queries. Each query has the form: [li, ri, ki, vi] For a query, we start at index li and repeatedly move forward by ki positions until we exceed ri . Every visited index is updated...

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3612 - Process String with Special Operations I

LeetCode Problem 3612 Difficulty: 🟡 Medium Topics: String, Simulation Solution Problem Understanding The problem asks us to simulate the construction of a string called result by processing an input string s from left to right. The input string contains lowercase English letters and three special operators: * , # , and % . Each character in the input modifies the evolving result string in a specific way. A lowercase letter...

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3614 - Process String with Special Operations II

LeetCode Problem 3614 Difficulty: 🔴 Hard Topics: String, Simulation Solution Problem Understanding The problem defines a transformation process over a string s that contains lowercase letters and three special operation characters: '*' , '#' , and '%' . We process the string from left to right, maintaining a dynamically changing result string. Each lowercase letter is appended to the result. The '*' operation deletes the last character of the result...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3597 - Partition String

LeetCode Problem 3597 Difficulty: 🟡 Medium Topics: Hash Table, String, Trie, Simulation Solution LeetCode 3597 - Partition String Problem Understanding We are given a string s and must partition it into segments according to a very specific process. We start at the current position in the string and begin building a segment character by character. As we extend the segment, we continuously check whether that exact segment has already appeared...

Practice › LeetCode › LeetCode 35xx ›

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...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3561 - Resulting String After Adjacent Removals

LeetCode Problem 3561 Difficulty: 🟡 Medium Topics: String, Stack, Simulation Solution Problem Understanding The problem asks us to repeatedly remove pairs of adjacent characters in a string that are consecutive in the alphabet, considering the alphabet as circular. "Consecutive in the alphabet" means two characters where the difference in their positions in the alphabet is 1, either forwards or backwards, and 'a' and 'z' are also considered consecutive. The operation...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3510 - Minimum Pair Removal to Sort Array II

LeetCode Problem 3510 Difficulty: 🔴 Hard Topics: Array, Hash Table, Linked List, Heap (Priority Queue), Simulation, Doubly-Linked List, Ordered Set Solution LeetCode 3510: Minimum Pair Removal to Sort Array II Problem Understanding We are given an array nums . The operation is highly constrained: Among all adjacent pairs, find the pair with the minimum sum. If multiple adjacent pairs have the same minimum sum, choose the leftmost one. Replace those...

Practice › LeetCode › LeetCode 35xx ›

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...

Practice › LeetCode › LeetCode 34xx ›

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' =...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3494 - Find the Minimum Amount of Time to Brew Potions

LeetCode Problem 3494 Difficulty: 🟡 Medium Topics: Array, Simulation, Prefix Sum Solution Problem Understanding The problem asks us to simulate a sequential brewing process for potions performed by a series of wizards. Each wizard has a skill level that determines the speed at which they brew a potion, while each potion has a mana requirement that affects how long it takes to brew. Specifically, the time for wizard i to...

Practice › LeetCode › LeetCode 34xx ›

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...

Practice › LeetCode › LeetCode 34xx ›

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...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3433 - Count Mentions Per User

LeetCode Problem 3433 Difficulty: 🟡 Medium Topics: Array, Math, Sorting, Simulation Solution LeetCode 3433 - Count Mentions Per User Problem Understanding This problem asks us to simulate a sequence of user activity events and count how many times each user is mentioned across all message events. We are given: numberOfUsers , the total number of users with IDs from 0 to numberOfUsers - 1 events , where each event is...

Practice › LeetCode › LeetCode 34xx ›

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...

Practice › LeetCode › LeetCode 36xx ›

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.

Practice › LeetCode › LeetCode 33xx ›

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...

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 22xx ›

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...

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...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3100 - Water Bottles II

LeetCode Problem 3100 Difficulty: 🟡 Medium Topics: Math, Simulation Solution Problem Understanding This problem models a bottle exchange process where the exchange rate increases after every successful trade. You start with numBottles full water bottles. Every time you drink a full bottle, it becomes an empty bottle. Empty bottles can then be exchanged for new full bottles, but there is an important rule: after each exchange, the required number of...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2352 - Equal Row and Column Pairs

LeetCode Problem 2352 Difficulty: 🟡 Medium Topics: Array, Hash Table, Matrix, Simulation Solution Problem Understanding The problem gives us a square matrix grid of size n x n , where every element is an integer. We need to count how many (row, column) pairs are exactly equal. More specifically, for every row ri and every column cj , we compare the sequence of elements in that row with the sequence...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2056 - Number of Valid Move Combinations On Chessboard

LeetCode Problem 2056 Difficulty: 🔴 Hard Topics: Array, String, Backtracking, Simulation Solution Problem Understanding The problem asks us to calculate the total number of valid move combinations for a small set of chess pieces (up to four) on an 8 x 8 chessboard. Each piece-rook, bishop, or queen-can move according to standard chess rules, but only along paths defined by the piece's movement. A move combination consists of assigning a...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2079 - Watering Plants

LeetCode Problem 2079 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding This problem asks us to simulate watering a row of plants with a watering can that has a fixed capacity. The plants are arranged along a straight line with indices representing their positions. You start at a river located at position x = -1 where you can refill your watering can. Each plant requires a specific amount of...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2365 - Task Scheduler II

LeetCode Problem 2365 Difficulty: 🟡 Medium Topics: Array, Hash Table, Simulation Solution Problem Understanding The problem gives us an array tasks , where each value represents a task type. The tasks must be completed strictly in the given order, which means we cannot rearrange them to optimize the schedule. We are also given an integer space . After completing a task of a certain type, we must wait at least...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2043 - Simple Bank System

LeetCode Problem 2043 Difficulty: 🟡 Medium Topics: Array, Hash Table, Design, Simulation Solution Problem Understanding This problem asks us to design a very simple banking system that supports three operations: Transfer money between two accounts Deposit money into an account Withdraw money from an account The bank contains n accounts numbered from 1 to n . The initial balance for each account is given in a 0-indexed array named balance...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3175 - Find The First Player to win K Games in a Row

LeetCode Problem 3175 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding The problem describes a competition where players stand in a queue and repeatedly compete against each other. Every player has a unique skill value, and whenever two players play, the one with the larger skill always wins. At each step: The first two players in the queue compete. The stronger player stays at the front. The weaker player...

Practice › LeetCode › LeetCode 19xx ›

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'...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3066 - Minimum Operations to Exceed Threshold Value II

LeetCode Problem 3066 Difficulty: 🟡 Medium Topics: Array, Heap (Priority Queue), Simulation Solution Problem Understanding This problem asks us to repeatedly combine the two smallest elements of an array nums until all elements are greater than or equal to a threshold value k . The combination operation is not a simple sum, but a formula: min(x, y) * 2 + max(x, y) . Essentially, this operation increases the smaller numbers...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2177 - Find Three Consecutive Integers That Sum to a Given Number

LeetCode Problem 2177 Difficulty: 🟡 Medium Topics: Math, Simulation Solution LeetCode 2177 - Find Three Consecutive Integers That Sum to a Given Number Problem Understanding This problem asks us to determine whether a given integer num can be represented as the sum of three consecutive integers. If such a representation exists, we must return those three integers in sorted order. Otherwise, we return an empty array. Three consecutive integers always...

Practice › LeetCode › LeetCode 33xx ›

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...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1860 - Incremental Memory Leak

LeetCode Problem 1860 Difficulty: 🟡 Medium Topics: Math, Simulation Solution Problem Understanding The problem models a faulty program that continuously consumes memory over time. There are two memory sticks, represented by the integers memory1 and memory2 . At each second, the program allocates an increasing number of bits: At second 1 , it allocates 1 bit. At second 2 , it allocates 2 bits. At second 3 , it allocates...

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...

Practice › LeetCode › LeetCode 33xx ›

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 25xx ›

LeetCode 2596 - Check Knight Tour Configuration

LeetCode Problem 2596 Difficulty: 🟡 Medium Topics: Array, Depth-First Search, Breadth-First Search, Matrix, Simulation Solution Problem Understanding The problem gives us an n x n matrix called grid , where every number from 0 to n * n - 1 appears exactly once. Each value represents the order in which a knight visited that cell during a tour of the chessboard. A knight in chess moves in an L-shape. From...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2221 - Find Triangular Sum of an Array

LeetCode Problem 2221 Difficulty: 🟡 Medium Topics: Array, Math, Simulation, Combinatorics, Number Theory Solution Problem Understanding The problem asks us to compute the triangular sum of an array of digits. The triangular sum is obtained by repeatedly reducing the array according to a simple rule: for every pair of adjacent elements, sum them modulo 10 to form a new array of length one less than the current array. This reduction...

Practice › LeetCode › LeetCode 26xx ›

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....

Practice › LeetCode › LeetCode 25xx ›

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...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2534 - Time Taken to Cross the Door

LeetCode Problem 2534 Difficulty: 🔴 Hard Topics: Array, Queue, Simulation Solution Problem Understanding This problem asks us to simulate how people pass through a single door over time while following a specific priority policy. Every person arrives at a certain second and wants to either enter or exit. Only one person may use the door per second, and when multiple people are waiting, the rules determine who gets priority. The...

Practice › LeetCode › LeetCode 30xx ›

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...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3266 - Final Array State After K Multiplication Operations II

LeetCode Problem 3266 Difficulty: 🔴 Hard Topics: Array, Heap (Priority Queue), Simulation Solution LeetCode 3266 - Final Array State After K Multiplication Operations II Problem Understanding The problem gives us an integer array nums , an integer k , and an integer multiplier . We must perform exactly k operations on the array. In each operation, we locate the minimum value currently present in the array. If multiple elements share...

Practice › LeetCode › LeetCode 32xx ›

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...

Practice › LeetCode › LeetCode 19xx ›

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 19xx ›

LeetCode 1910 - Remove All Occurrences of a Substring

LeetCode Problem 1910 Difficulty: 🟡 Medium Topics: String, Stack, Simulation Solution Problem Understanding The problem asks us to repeatedly remove occurrences of a substring part from a string s . The important detail is that on every operation, we must remove the leftmost occurrence of part . We continue performing removals until part no longer appears anywhere inside s . In simpler terms, we scan the string, remove one matching...

Practice › LeetCode › LeetCode 29xx ›

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...

Practice › LeetCode › LeetCode 23xx ›

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...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2161 - Partition Array According to Given Pivot

LeetCode Problem 2161 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Simulation Solution Problem Understanding This problem asks us to rearrange an array around a given pivot value while preserving relative ordering inside certain groups. We are given an integer array nums and an integer pivot . The goal is to reorganize the array into three consecutive sections: All elements smaller than pivot All elements equal to pivot All elements greater...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2482 - Difference Between Ones and Zeros in Row and Column

LeetCode Problem 2482 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution LeetCode 2482 - Difference Between Ones and Zeros in Row and Column Problem Understanding The problem gives us a binary matrix grid with m rows and n columns. Every cell contains either 0 or 1 . We must construct another matrix called diff , where each position diff[i][j] depends on how many ones and zeros appear in row i...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3160 - Find the Number of Distinct Colors Among the Balls

LeetCode Problem 3160 Difficulty: 🟡 Medium Topics: Array, Hash Table, Simulation Solution Problem Understanding The problem gives us limit + 1 balls labeled from 0 to limit . Initially, none of the balls have a color assigned. We then process a sequence of queries, where each query is of the form [x, y] . This means ball x should now be painted with color y . The important detail is...

Practice › LeetCode › LeetCode 23xx ›

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 23xx ›

LeetCode 2390 - Removing Stars From a String

LeetCode Problem 2390 Difficulty: 🟡 Medium Topics: String, Stack, Simulation Solution Problem Understanding This problem asks us to repeatedly process a string that contains lowercase English letters and star characters ( * ). Every star represents a removal operation. When we encounter a star, we must remove two things: The star itself. The closest non-star character immediately to its left. We continue this process until all stars have been removed....

Practice › LeetCode › LeetCode 32xx ›

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...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2211 - Count Collisions on a Road

LeetCode Problem 2211 Difficulty: 🟡 Medium Topics: String, Stack, Simulation Solution LeetCode 2211 - Count Collisions on a Road Problem Understanding The problem describes a one dimensional road containing cars positioned from left to right. Every car has one of three possible states: 'L' , meaning the car moves left 'R' , meaning the car moves right 'S' , meaning the car stays stationary All moving cars travel at the...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2069 - Walking Robot Simulation II

LeetCode Problem 2069 Difficulty: 🟡 Medium Topics: Design, Simulation Solution Problem Understanding The problem describes a simulation of a robot moving on a rectangular grid defined by width x height . The robot starts at the bottom-left corner (0, 0) facing East and moves in discrete steps. Each step moves the robot forward in its current direction unless the next cell is out of bounds, in which case the robot...

Practice › LeetCode › LeetCode 20xx ›

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...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2061 - Number of Spaces Cleaning Robot Cleaned

LeetCode Problem 2061 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding In this problem, we are given a 2D binary matrix called room . Each cell represents a position in the room: 0 means the space is empty and can be cleaned. 1 means the space contains an object and cannot be entered. A cleaning robot starts at the top-left corner (0, 0) , and the problem guarantees...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3324 - Find the Sequence of Strings Appeared on the Screen

LeetCode Problem 3324 Difficulty: 🟡 Medium Topics: String, Simulation Solution Problem Understanding The problem gives us a target string and a very restricted keyboard with only two operations. The first key always appends the character "a" to the end of the current string. The second key changes only the last character of the current string to the next letter in the alphabet. For example: "a" becomes "b" "b" becomes "c"...

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 25xx ›

LeetCode 2507 - Smallest Value After Replacing With Sum of Prime Factors

LeetCode Problem 2507 Difficulty: 🟡 Medium Topics: Math, Simulation, Number Theory Solution Problem Understanding The problem asks us to repeatedly replace a number n with the sum of its prime factors until it reaches the smallest value it can take. Prime factors should be counted with multiplicity, meaning that if a prime factor divides n multiple times, it is added to the sum as many times as it divides n...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2751 - Robot Collisions

LeetCode Problem 2751 Difficulty: 🔴 Hard Topics: Array, Stack, Sorting, Simulation Solution Problem Understanding This problem describes a simulation of robots moving on a one-dimensional line, each with a given starting position, health, and direction. Every robot moves at the same speed, and collisions occur when two robots meet at the same position. The key rules are: if two robots collide, the one with lower health is removed, the one...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2289 - Steps to Make Array Non-decreasing

LeetCode Problem 2289 Difficulty: 🟡 Medium Topics: Array, Linked List, Dynamic Programming, Stack, Monotonic Stack, Simulation Solution Problem Understanding The problem asks us to determine how many steps it takes to make a given array nums non-decreasing by repeatedly removing elements that break the non-decreasing property. Specifically, for each step, any element nums[i] where nums[i - 1] > nums[i] is removed. This process continues until the array is entirely non-decreasing....

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2679 - Sum in a Matrix

LeetCode Problem 2679 Difficulty: 🟡 Medium Topics: Array, Sorting, Heap (Priority Queue), Matrix, Simulation Solution Problem Understanding The problem gives us a 2D integer matrix nums . Each row contains several integers, and we repeatedly perform a special removal process until every element has been removed. During each operation, we do two things: From every row, remove the largest remaining element. Among all removed elements from this round, take the...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3271 - Hash Divided String

LeetCode Problem 3271 Difficulty: 🟡 Medium Topics: String, Simulation Solution Problem Understanding The problem asks us to compute a hashed string from an input string s by dividing it into equal-length substrings and then mapping each substring to a single character using a simple hashing function. Specifically, for each substring of length k , we compute the sum of the positions of its characters in the English alphabet (where 'a'...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2181 - Merge Nodes in Between Zeros

LeetCode Problem 2181 Difficulty: 🟡 Medium Topics: Linked List, Simulation Solution Problem Understanding The problem gives us a singly linked list where the values are grouped between 0 nodes. The list always starts with 0 and ends with 0 , and there are no two consecutive zeros. Every sequence of non-zero nodes between two zeros represents one group. Our task is to replace each group with a single node whose...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3279 - Maximum Total Area Occupied by Pistons

LeetCode Problem 3279 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Simulation, Counting, Prefix Sum Solution Problem Understanding This problem is about simulating the motion of pistons in a car engine and computing the maximum total area under the pistons over time. Each piston moves either up or down by 1 unit every second, reversing direction when it hits the top ( height ) or bottom ( 0 ). The...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3237 - Alt and Tab Simulation

LeetCode Problem 3237 Difficulty: 🟡 Medium Topics: Array, Hash Table, Simulation Solution Problem Understanding The problem asks us to simulate the behavior of switching between open windows using the classic Alt + Tab operation. We are given an array called windows , which represents the current ordering of open windows. The first element of the array is the window currently on top, and the last element is the window at...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3080 - Mark Elements on Array by Performing Queries

LeetCode Problem 3080 Difficulty: 🟡 Medium Topics: Array, Hash Table, Sorting, Heap (Priority Queue), Simulation Solution Here’s a fully detailed technical solution guide for LeetCode 3080 following your requested format. Problem Understanding The problem gives a zero-indexed array nums of size n consisting of positive integers and a 2D array queries of size m where each query is [indexi, ki] . All elements of nums are initially unmarked. Each query...

Practice › LeetCode › LeetCode 27xx ›

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...

Practice › LeetCode › LeetCode 21xx ›

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...

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....

Practice › LeetCode › LeetCode 21xx ›

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...

Practice › LeetCode › LeetCode 31xx ›

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...

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...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2327 - Number of People Aware of a Secret

LeetCode Problem 2327 Difficulty: 🟡 Medium Topics: Dynamic Programming, Queue, Simulation Solution Problem Understanding The problem describes how a secret spreads over time. On day 1 , exactly one person knows the secret. Every person who learns the secret behaves according to two rules: They must wait delay days before they can begin sharing the secret. They forget the secret after forget days, and once they forget it, they can...

Practice › LeetCode › LeetCode 33xx ›

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...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2296 - Design a Text Editor

LeetCode Problem 2296 Difficulty: 🔴 Hard Topics: Linked List, String, Stack, Design, Simulation, Doubly-Linked List Solution Problem Understanding This problem asks us to design a simplified text editor that supports four operations: Inserting text at the current cursor position Deleting characters to the left of the cursor Moving the cursor left Moving the cursor right The cursor behaves exactly like a cursor in a normal text editor. It always sits...

Practice › LeetCode › LeetCode 25xx ›

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...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2109 - Adding Spaces to a String

LeetCode Problem 2109 Difficulty: 🟡 Medium Topics: Array, Two Pointers, String, Simulation Solution Problem Understanding The problem requires us to insert spaces into a given string s at specific positions described by the array spaces . Each element in spaces represents an index in the string before which a space should be inserted. For example, if spaces = [2] and s = "hello" , the output would be "he llo"...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2257 - Count Unguarded Cells in the Grid

LeetCode Problem 2257 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding This problem gives us an m x n grid containing three types of cells: Guard cells Wall cells Empty cells Each guard can observe cells in the four cardinal directions: Up Down Left Right A guard continues seeing cells in a direction until the view is blocked by either: A wall Another guard The task is to...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2532 - Time to Cross a Bridge

LeetCode Problem 2532 Difficulty: 🔴 Hard Topics: Array, Heap (Priority Queue), Simulation Solution Problem Understanding The problem asks us to simulate a scenario in which k workers transport n boxes from a right-side warehouse to a left-side warehouse across a bridge. Each worker has individual timings for four actions: crossing the bridge to the right ( righti ), picking up a box on the right ( picki ), crossing back...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3179 - Find the N-th Value After K Seconds

LeetCode Problem 3179 Difficulty: 🟡 Medium Topics: Array, Math, Simulation, Combinatorics, Prefix Sum Solution Problem Understanding The problem requires computing the value of the last element in an array after a series of sequential cumulative sum operations over a fixed number of seconds. You start with an array a of length n where all elements are initialized to 1. Every second, each element at index i becomes the sum of...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2766 - Relocate Marbles

LeetCode Problem 2766 Difficulty: 🟡 Medium Topics: Array, Hash Table, Sorting, Simulation Solution Problem Understanding The problem gives us an array nums representing the positions of marbles on a number line. Multiple marbles may exist at the same position, so nums can contain duplicates. We are also given two arrays, moveFrom and moveTo , which describe a sequence of move operations. For each index i , we must move every...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1894 - Find the Student that Will Replace the Chalk

LeetCode Problem 1894 Difficulty: 🟡 Medium Topics: Array, Binary Search, Simulation, Prefix Sum Solution Problem Understanding The problem presents a classroom scenario where students are given problems in a round-robin order, consuming a certain number of chalk pieces for each problem. We are given an array chalk , where chalk[i] indicates the number of chalk pieces student i uses, and an integer k representing the initial chalk supply. Starting from...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2402 - Meeting Rooms III

LeetCode Problem 2402 Difficulty: 🔴 Hard Topics: Array, Hash Table, Sorting, Heap (Priority Queue), Simulation Solution Problem Understanding The problem is about scheduling meetings into a fixed number of rooms, where each meeting has a unique start time and a defined duration. We have n rooms numbered from 0 to n - 1 , and we are given a list of meetings represented as [start, end) intervals. The task is...

Practice › LeetCode › LeetCode 31xx ›

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....

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2149 - Rearrange Array Elements by Sign

LeetCode Problem 2149 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Simulation Solution Problem Understanding The problem asks us to rearrange a given integer array nums such that positive and negative numbers alternate, starting with a positive number. The array has an even length and contains an equal number of positive and negative integers. In addition to alternating signs, the relative order of positive numbers among themselves and negative numbers among...

Practice › LeetCode › LeetCode 25xx ›

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...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2105 - Watering Plants II

LeetCode Problem 2105 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Simulation Solution Problem Understanding In this problem, we are given a row of plants where each plant requires a certain amount of water. Two people, Alice and Bob, water the plants simultaneously from opposite ends of the array. Alice starts from the left side at index 0 and moves toward the right. Bob starts from the right side at index...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1914 - Cyclically Rotating a Grid

LeetCode Problem 1914 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution LeetCode 1914 - Cyclically Rotating a Grid Problem Understanding The problem gives us an m x n matrix called grid , along with an integer k . Both dimensions of the matrix are guaranteed to be even numbers. The task is to rotate every layer of the matrix counter-clockwise exactly k times. A layer is the rectangular ring formed...

Practice › LeetCode › LeetCode 20xx ›

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...

Practice › LeetCode › LeetCode 32xx ›

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...

Practice › LeetCode › LeetCode 21xx ›

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...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2295 - Replace Elements in an Array

LeetCode Problem 2295 Difficulty: 🟡 Medium Topics: Array, Hash Table, Simulation Solution Problem Understanding The problem asks us to perform a series of replacement operations on an array of distinct integers. Specifically, we have an initial array nums containing n distinct positive integers. We are also given m operations, each consisting of a pair [oldValue, newValue] . For each operation, we must locate the element oldValue in the array and...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3400 - Maximum Number of Matching Indices After Right Shifts

LeetCode Problem 3400 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Simulation Solution Problem Understanding The problem gives us two arrays, nums1 and nums2 , both of the same length n . We are allowed to repeatedly perform a right circular shift on nums1 . A right shift moves every element one position to the right, and the last element wraps around to the beginning. For example: [1, 2, 3, 4]...

Practice › LeetCode › LeetCode 28xx ›

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...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2961 - Double Modular Exponentiation

LeetCode Problem 2961 Difficulty: 🟡 Medium Topics: Array, Math, Simulation Solution Problem Understanding The problem gives us a 0-indexed 2D array called variables , where each element contains four integers: ai bi ci mi For each index i , we must evaluate the following mathematical expression: $$((a_i^{b_i} \bmod 10)^{c_i}) \bmod m_i$$ If the result equals the given integer target , then index i is considered a good index . Our...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2326 - Spiral Matrix IV

LeetCode Problem 2326 Difficulty: 🟡 Medium Topics: Array, Linked List, Matrix, Simulation Solution Problem Understanding The problem gives us a linked list and asks us to place its values into an m x n matrix in clockwise spiral order. We begin filling from the top-left corner of the matrix, which is position (0, 0) . The traversal direction follows the standard spiral pattern: Move left to right across the top...

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...

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...

Practice › LeetCode › LeetCode 32xx ›

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...

Practice › LeetCode › LeetCode 29xx ›

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...

Practice › LeetCode › LeetCode 26xx ›

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...

Practice › LeetCode › LeetCode 22xx ›

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,...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2593 - Find Score of an Array After Marking All Elements

LeetCode Problem 2593 Difficulty: 🟡 Medium Topics: Array, Hash Table, Sorting, Heap (Priority Queue), Simulation Solution Here is a comprehensive, detailed technical solution guide for LeetCode 2593 - Find Score of an Array After Marking All Elements , following your requested format precisely. Problem Understanding The problem provides an array of positive integers, nums . We are asked to simulate a scoring process where at each step we select the...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2201 - Count Artifacts That Can Be Extracted

LeetCode Problem 2201 Difficulty: 🟡 Medium Topics: Array, Hash Table, Simulation Solution Problem Understanding This problem models an excavation process on a square n x n grid. Several rectangular artifacts are buried in the grid, and each artifact occupies one or more cells. Every artifact is described by four integers: (r1, c1) represents the top-left corner (r2, c2) represents the bottom-right corner This means the artifact occupies every cell inside...

Practice › LeetCode › LeetCode 24xx ›

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...

Practice › LeetCode › LeetCode 30xx ›

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 31xx ›

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...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2075 - Decode the Slanted Ciphertext

LeetCode Problem 2075 Difficulty: 🟡 Medium Topics: String, Simulation Solution Problem Understanding The problem requires decoding a string that was encoded using a slanted transposition cipher . In this cipher, the original text is written diagonally in a grid with a fixed number of rows. Specifically, the placement starts at the top-left and moves down and to the right in a zig-zag manner. After filling the grid, the encoded string...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3072 - Distribute Elements Into Two Arrays II

LeetCode Problem 3072 Difficulty: 🔴 Hard Topics: Array, Binary Indexed Tree, Segment Tree, Simulation Solution Problem Understanding This problem requires simulating the distribution of elements from a 1-indexed array nums into two separate arrays arr1 and arr2 under specific rules. Each element in nums is assigned sequentially to one of the arrays according to a comparison of how many elements in each array are strictly greater than the current element....

Practice › LeetCode › LeetCode 25xx ›

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...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2462 - Total Cost to Hire K Workers

LeetCode Problem 2462 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Heap (Priority Queue), Simulation Solution Problem Understanding The problem asks us to simulate a process of hiring k workers from a list costs , where each worker has an associated cost. We can hire workers only from the first candidates workers or the last candidates workers in each hiring session. The goal is to compute the total cost incurred after...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2502 - Design Memory Allocator

LeetCode Problem 2502 Difficulty: 🟡 Medium Topics: Array, Hash Table, Design, Simulation Solution Problem Understanding The problem requires designing a memory allocator that manages a fixed-size memory array. Initially, all memory units are free, and the allocator supports two operations: allocating a block of consecutive free memory units for a given ID ( mID ) and freeing all memory units associated with a given mID . Allocation should always select...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2380 - Time Needed to Rearrange a Binary String

LeetCode Problem 2380 Difficulty: 🟡 Medium Topics: String, Dynamic Programming, Simulation Solution Problem Understanding This problem asks us to repeatedly transform a binary string according to a very specific rule. During each second, every occurrence of the substring "01" is replaced simultaneously with "10" . The important detail is that all replacements happen at the same time. This means we do not process one occurrence at a time from left...

Practice › LeetCode › LeetCode 27xx ›

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...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1823 - Find the Winner of the Circular Game

LeetCode Problem 1823 Difficulty: 🟡 Medium Topics: Array, Math, Recursion, Queue, Simulation Solution Problem Understanding The problem describes a variation of the classic Josephus problem. We have n friends sitting in a circle, numbered 1 through n clockwise. Starting from the first friend, we count k friends clockwise (inclusive of the starting friend). The friend at the k -th position is removed from the circle. The counting then resumes from...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 158 - Read N Characters Given read4 II - Call Multiple Times

LeetCode Problem 158 Difficulty: 🔴 Hard Topics: Array, Simulation, Interactive Solution Problem Understanding This problem asks us to implement a read(buf, n) function using a restricted API called read4(buf4) . The challenge is that we are not allowed to access the file directly, instead, we can only retrieve data in chunks of up to four characters at a time. At first glance, this may look very similar to LeetCode 157,...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 544 - Output Contest Matches

LeetCode Problem 544 Difficulty: 🟡 Medium Topics: String, Recursion, Simulation Solution Problem Understanding The problem asks us to simulate the structure of a playoff tournament bracket. We are given n teams, numbered from 1 to n , where smaller numbers represent stronger teams. The tournament pairing rule is fixed: in every round, the strongest remaining team must play against the weakest remaining team. The output is not the winner of...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 54 - Spiral Matrix

LeetCode Problem 54 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding The problem gives an m x n matrix and asks us to return all elements in spiral order. Spiral order means we start from the top-left corner and move in a clockwise spiral pattern: Traverse the top row from left to right Traverse the right column from top to bottom Traverse the bottom row from right to...

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 10xx ›

LeetCode 1041 - Robot Bounded In Circle

LeetCode Problem 1041 Difficulty: 🟡 Medium Topics: Math, String, Simulation Solution Problem Understanding This problem asks us to determine whether a robot moving on an infinite two dimensional plane will remain within some bounded region if it repeats a sequence of instructions forever. The robot starts at coordinate (0, 0) facing north. The input is a string called instructions , where each character represents an action: 'G' means move forward...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1409 - Queries on a Permutation With Key

LeetCode Problem 1409 Difficulty: 🟡 Medium Topics: Array, Binary Indexed Tree, Simulation Solution Problem Understanding This problem asks us to simulate a dynamic permutation of integers and answer position queries as elements continuously move. Initially, we are given a permutation: P = [1, 2, 3, ..., m] For every value in the queries array, we must perform two operations: Find the current position of queries[i] in the permutation P ,...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1404 - Number of Steps to Reduce a Number in Binary Representation to One

LeetCode Problem 1404 Difficulty: 🟡 Medium Topics: String, Bit Manipulation, Simulation Solution Problem Understanding The problem gives us a binary number represented as a string s . Our task is to determine how many operations are required to reduce this number to exactly 1 . The allowed operations depend on whether the current value is even or odd: If the number is even, divide it by 2 If the number...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2120 - Execution of All Suffix Instructions Staying in a Grid

LeetCode Problem 2120 Difficulty: 🟡 Medium Topics: String, Simulation Solution Problem Understanding The problem asks us to simulate a robot moving on an n x n grid, starting from a specified position startPos = [startrow, startcol] . We are given a sequence of movement instructions as a string s , where each character represents a direction: 'L' for left, 'R' for right, 'U' for up, and 'D' for down. The...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 289 - Game of Life

LeetCode Problem 289 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding The problem asks us to simulate one iteration of Conway's Game of Life on a two-dimensional grid. Each cell in the grid is either alive, represented by 1 , or dead, represented by 0 . Every cell changes state simultaneously according to the number of live neighbors surrounding it. Each cell has up to eight neighbors, including...

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 16xx ›

LeetCode 1680 - Concatenation of Consecutive Binary Numbers

LeetCode Problem 1680 Difficulty: 🟡 Medium Topics: Math, Bit Manipulation, Simulation Solution Problem Understanding The problem asks us to build a very large binary number by concatenating the binary representations of every integer from 1 through n , in order, and then return its decimal value modulo 10^9 + 7 . For example, if n = 3 : 1 in binary is "1" 2 in binary is "10" 3 in...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1535 - Find the Winner of an Array Game

LeetCode Problem 1535 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding The problem describes a competitive game played on an array of distinct integers . At every round, only the first two elements are compared. The larger number wins the round and stays at the front of the array, while the smaller number is moved to the end. This process repeats until one number achieves k consecutive wins ....

Practice › LeetCode › LeetCode 06xx ›

LeetCode 640 - Solve the Equation

LeetCode Problem 640 Difficulty: 🟡 Medium Topics: Math, String, Simulation Solution Problem Understanding The problem is asking us to solve a linear equation containing a single variable 'x' and integer coefficients, expressed as a string. The equation may include addition '+' , subtraction '-' , and the equality operator '=' . We need to parse this string, combine like terms, and solve for 'x' . The result should be returned...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1706 - Where Will the Ball Fall

LeetCode Problem 1706 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding This problem asks us to simulate the movement of balls dropped into a 2-D box represented by a grid. Each cell in the grid has a diagonal board that directs a ball either to the right ( 1 ) or to the left ( -1 ). We drop one ball into each column at the top of...

Practice › LeetCode › LeetCode 12xx ›

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:...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 755 - Pour Water

LeetCode Problem 755 Difficulty: 🟡 Medium Topics: Array, Simulation Solution LeetCode 755 - Pour Water Problem Understanding This problem asks us to simulate how water droplets behave when poured onto a one-dimensional terrain. The terrain is represented by the array heights , where each element describes the height of a column at that position. We are also given: volume , the number of water droplets to pour k , the...

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 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 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 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 04xx ›

LeetCode 498 - Diagonal Traverse

LeetCode Problem 498 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding This problem asks us to traverse a matrix in a specific diagonal pattern and return all elements in the order they are visited. We are given an m x n matrix mat , where m represents the number of rows and n represents the number of columns. The goal is to return a one dimensional array containing...

Practice › LeetCode › LeetCode 12xx ›

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...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 348 - Design Tic-Tac-Toe

LeetCode Problem 348 Difficulty: 🟡 Medium Topics: Array, Hash Table, Design, Matrix, Simulation Solution Problem Understanding The problem asks us to design a data structure that simulates an n x n Tic-Tac-Toe game between two players. We need to implement a class that supports two operations: Initializing a game board of size n Processing moves one at a time and immediately determining whether the current move causes a player to...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1503 - Last Moment Before All Ants Fall Out of a Plank

LeetCode Problem 1503 Difficulty: 🟡 Medium Topics: Array, Brainteaser, Simulation Solution Problem Understanding The problem describes a plank of length n on which ants are walking either to the left or to the right at a constant speed of 1 unit per second. We are given two arrays: left contains the starting positions of ants moving left, and right contains the starting positions of ants moving right. When two ants...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1222 - Queens That Can Attack the King

LeetCode Problem 1222 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding In this problem, we are given the positions of several black queens and exactly one white king on a standard 8 x 8 chessboard. The board uses 0-indexed coordinates, meaning every position is represented as [row, column] , where both values range from 0 to 7 . A queen in chess can attack along eight possible directions:...

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 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 04xx ›

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 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 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 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 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 15xx ›

LeetCode 1545 - Find Kth Bit in Nth Binary String

LeetCode Problem 1545 Difficulty: 🟡 Medium Topics: String, Recursion, Simulation Solution Problem Understanding The problem defines a recursively constructed binary string sequence: S1 = "0" Si = Si-1 + "1" + reverse(invert(Si-1)) For every new level, we take the previous string, append "1" , then append the reversed and bit-inverted version of the previous string. The task is to return the kth bit in the string Sn . To understand...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1801 - Number of Orders in the Backlog

LeetCode Problem 1801 Difficulty: 🟡 Medium Topics: Array, Heap (Priority Queue), Simulation Solution Problem Understanding This problem simulates a simplified stock exchange order book. Each incoming order is either a buy order or a sell order, and each order contains a price and an amount. Orders are processed strictly in the order they appear in the input. A buy order wants to purchase shares at a certain maximum price. A...

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 00xx ›

LeetCode 43 - Multiply Strings

LeetCode Problem 43 Difficulty: 🟡 Medium Topics: Math, String, Simulation Solution Problem Understanding The problem asks us to multiply two non-negative integers where each integer is provided as a string instead of a numeric type. The result must also be returned as a string. The important restriction is that we cannot directly convert the strings into integers or use any built-in big integer library. In other words, we must manually...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1806 - Minimum Number of Operations to Reinitialize a Permutation

LeetCode Problem 1806 Difficulty: 🟡 Medium Topics: Array, Math, Simulation Solution Problem Understanding The problem gives us an even integer n and defines an initial permutation: perm[i] = i This means the array initially looks like: [0, 1, 2, 3, ..., n - 1] We repeatedly apply a transformation rule to build a new array arr : If the index i is even: arr[i] = perm[i / 2] If the...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 950 - Reveal Cards In Increasing Order

LeetCode Problem 950 Difficulty: 🟡 Medium Topics: Array, Queue, Sorting, Simulation Solution Problem Understanding The problem gives us a deck of unique integer cards and asks us to arrange the deck so that a very specific reveal process produces the cards in increasing order. The reveal process works like this: Reveal the top card and remove it from the deck. Move the next top card to the bottom of the...

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 07xx ›

LeetCode 749 - Contain Virus

LeetCode Problem 749 Difficulty: 🔴 Hard Topics: Array, Depth-First Search, Breadth-First Search, Matrix, Simulation Solution Problem Understanding This problem models the spread of a virus on a two-dimensional grid. Each cell is either infected ( 1 ) or uninfected ( 0 ). The virus spreads every night from infected cells to adjacent uninfected cells in the four cardinal directions: up, down, left, and right. We are allowed to build walls...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1701 - Average Waiting Time

LeetCode Problem 1701 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding This problem is asking us to simulate the operation of a single-chef restaurant, where customers arrive at certain times and each customer has a specific preparation time for their order. The goal is to calculate the average waiting time for all customers. The waiting time for a customer is the total time they spend in the system from...

Practice › LeetCode › LeetCode 08xx ›

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...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 59 - Spiral Matrix II

LeetCode Problem 59 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution LeetCode 59 - Spiral Matrix II Problem Understanding The problem asks us to generate an n x n matrix and fill it with numbers from 1 to n^2 in spiral order. A spiral order traversal means we begin at the top-left corner and move in a clockwise pattern: Move left to right across the top row Move top to...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1441 - Build an Array With Stack Operations

LeetCode Problem 1441 Difficulty: 🟡 Medium Topics: Array, Stack, Simulation Solution Problem Understanding The problem gives us a strictly increasing array called target and an integer n . We are also given access to a stream of integers starting from 1 and ending at n . The numbers arrive in order, and once a number is skipped, we cannot go back to it. We start with an empty stack and...

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 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 13xx ›

LeetCode 1324 - Print Words Vertically

LeetCode Problem 1324 Difficulty: 🟡 Medium Topics: Array, String, Simulation Solution Problem Understanding The problem requires us to take a string s containing multiple words separated by single spaces and return a list of strings representing the words written vertically. In other words, each column of the output corresponds to characters from the original words at the same position. If a word is shorter than the longest word, missing characters...

Practice › LeetCode › LeetCode 16xx ›

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...

Practice › LeetCode › LeetCode 01xx ›

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...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 723 - Candy Crush

LeetCode Problem 723 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Matrix, Simulation Solution Problem Understanding This problem is essentially a simulation of the Candy Crush game, where we need to repeatedly crush candies in a grid until the board reaches a stable state. The input is an m x n matrix of integers representing different types of candies, and 0 represents empty cells. Each integer from 1 to 2000 represents...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 874 - Walking Robot Simulation

LeetCode Problem 874 Difficulty: 🟡 Medium Topics: Array, Hash Table, Simulation Solution Problem Understanding The problem describes a robot moving on an infinite two dimensional grid. The robot begins at coordinate (0, 0) and initially faces north, which corresponds to the positive Y direction. The robot processes a sequence of commands, where each command either changes its direction or moves it forward. There are three kinds of commands: -2 means...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 537 - Complex Number Multiplication

LeetCode Problem 537 Difficulty: 🟡 Medium Topics: Math, String, Simulation Solution Problem Understanding This problem asks us to multiply two complex numbers represented as strings and return the result in the same string format. A complex number is written as: "real+imaginaryi" For example: "1+1i" represents $1 + i$ "1+-1i" represents $1 - i$ The input strings always follow a valid format, meaning we do not need to worry about malformed...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1562 - Find Latest Group of Size M

LeetCode Problem 1562 Difficulty: 🟡 Medium Topics: Array, Hash Table, Binary Search, Simulation Solution Edit LeetCode 1562 - Find Latest Group of Size M Problem Understanding This problem gives us a permutation array arr containing integers from 1 to n , where n is the size of the binary string we are building. Initially, the binary string contains only zeroes. At each step, we flip exactly one position from 0...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 946 - Validate Stack Sequences

LeetCode Problem 946 Difficulty: 🟡 Medium Topics: Array, Stack, Simulation Solution Problem Understanding This problem asks whether two sequences of integers, pushed and popped , could represent valid operations on a stack. The pushed array represents the order in which elements are pushed onto an initially empty stack, while the popped array represents the order in which elements are popped from the stack. The task is to determine if the...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 353 - Design Snake Game

LeetCode Problem 353 Difficulty: 🟡 Medium Topics: Array, Hash Table, Design, Queue, Simulation Solution Problem Understanding The problem asks us to design a mutable data structure that simulates the classic Snake game. The game is played on a rectangular grid with dimensions height x width . The snake starts at the top-left corner (0, 0) and initially has length 1 . The game receives a predefined sequence of food positions....

Practice › LeetCode › LeetCode 05xx ›

LeetCode 592 - Fraction Addition and Subtraction

LeetCode Problem 592 Difficulty: 🟡 Medium Topics: Math, String, Simulation Solution Problem Understanding The problem requires computing the result of a mathematical expression containing fractions with addition and subtraction operators. The input is a single string, expression , which consists of positive or negative fractions in the format numerator/denominator . The output must be an irreducible fraction, represented as a string in the same format. If the result is an...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 68 - Text Justification

LeetCode Problem 68 Difficulty: 🔴 Hard Topics: Array, String, Simulation Solution LeetCode 68 - Text Justification Problem Understanding This problem asks us to simulate how text is formatted in a text editor when using full justification. We are given an array of words and a target line width called maxWidth . The goal is to arrange these words into multiple lines such that every line contains exactly maxWidth characters. The...

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 16xx ›

LeetCode 1606 - Find Servers That Handled Most Number of Requests

LeetCode Problem 1606 Difficulty: 🔴 Hard Topics: Array, Heap (Priority Queue), Simulation, Ordered Set Solution Problem Understanding The problem presents a simulation scenario involving k servers, each uniquely identified from 0 to k-1 . Every server can handle only one request at a time , and requests arrive at discrete times given by the strictly increasing arrival array. Each request requires a certain load of time to complete. Requests are...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2028 - Find Missing Observations

LeetCode Problem 2028 Difficulty: 🟡 Medium Topics: Array, Math, Simulation Solution Problem Understanding The problem gives us the results of some dice rolls and asks us to reconstruct the missing ones. We have a total of n + m rolls of a standard 6-sided die. Out of those rolls: m values are known and stored in the array rolls n values are missing the average of all n + m...

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 17xx ›

LeetCode 1719 - Number Of Ways To Reconstruct A Tree

LeetCode Problem 1719 Difficulty: 🔴 Hard Topics: Array, Hash Table, Tree, Graph Theory, Simulation Solution Problem Understanding The problem provides an array of pairs , where each pair [xi, yi] indicates that xi is either an ancestor of yi or yi is an ancestor of xi in a rooted tree. The key challenge is to determine how many different rooted trees satisfy all given pairs. We are not limited to...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1094 - Car Pooling

LeetCode Problem 1094 Difficulty: 🟡 Medium Topics: Array, Sorting, Heap (Priority Queue), Simulation, Prefix Sum Solution Problem Understanding This problem asks us to determine whether a car can successfully complete a series of passenger trips without ever exceeding its seating capacity. Each trip is represented as: [numPassengers, from, to] This means: numPassengers passengers enter the car at location from Those same passengers leave the car at location to The important...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1599 - Maximum Profit of Operating a Centennial Wheel

LeetCode Problem 1599 Difficulty: 🟡 Medium Topics: Array, Simulation Solution LeetCode 1599 - Maximum Profit of Operating a Centennial Wheel Problem Understanding This problem asks us to simulate the operation of a Centennial Wheel and determine the minimum number of rotations required to achieve the maximum possible profit. The wheel has four gondolas, and each gondola can hold at most four people during a single rotation. Customers arrive over time...

Practice › LeetCode › LeetCode 16xx ›

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....

Practice › LeetCode › LeetCode 07xx ›

LeetCode 735 - Asteroid Collision

LeetCode Problem 735 Difficulty: 🟡 Medium Topics: Array, Stack, Simulation Solution Problem Understanding The problem gives us a list of integers representing asteroids moving through space in a straight line. Each integer contains two pieces of information: The absolute value represents the asteroid's size. The sign represents the direction: Positive numbers move to the right. Negative numbers move to the left. All asteroids move at the same speed. When two...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1583 - Count Unhappy Friends

LeetCode Problem 1583 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding In this problem, we are given n friends, where n is always even. Every friend ranks all other friends in order of preference. The earlier someone appears in a person's preference list, the more that person is preferred. We are also given a final pairing arrangement. Each person is paired with exactly one other person. The goal is...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1006 - Clumsy Factorial

LeetCode Problem 1006 Difficulty: 🟡 Medium Topics: Math, Stack, Simulation Solution Problem Understanding The problem asks us to compute a clumsy factorial for a given positive integer n . A standard factorial multiplies all integers from n down to 1 , but the clumsy factorial modifies the operations: instead of multiplying all numbers, it cycles through '*' , '/' , '+' , and '-' in that order, applying the operations...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 885 - Spiral Matrix III

LeetCode Problem 885 Difficulty: 🟡 Medium Topics: Array, Matrix, Simulation Solution Problem Understanding The problem is asking us to generate the coordinates of cells in a 2D grid that we would visit if we started at a given cell (rStart, cStart) and walked in a clockwise spiral pattern. The grid has dimensions rows x cols , and the top-left corner is (0, 0) while the bottom-right corner is (rows -...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1756 - Design Most Recently Used Queue

LeetCode Problem 1756 Difficulty: 🟡 Medium Topics: Array, Linked List, Divide and Conquer, Design, Simulation, Doubly-Linked List Solution Problem Understanding The problem asks us to design a special queue called an "Most Recently Used Queue", abbreviated as MRUQueue. Initially, the queue contains the integers from 1 to n in increasing order. The key operation is fetch(k) , where k is 1-indexed. This operation does two things: It finds the kth...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 985 - Sum of Even Numbers After Queries

LeetCode Problem 985 Difficulty: 🟡 Medium Topics: Array, Simulation Solution Problem Understanding The problem gives us an integer array nums and a list of update operations called queries . Each query contains two values: vali , the amount to add indexi , the position in the array to update For every query, we must first update the array element: nums[indexi] = nums[indexi] + vali After applying the update, we must...

Practice › LeetCode › LeetCode 11xx ›

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 13xx ›

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...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1006: Clumsy Factorial

Problem Restatement The clumsy factorial of a positive integer n is defined as follows: Start from n and apply operators * , / , + , - in a fixed cyclic order, descending through integers. For example, clumsy(10) = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1 . Division is integer division truncated toward zero. We need to return...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1073: Adding Negative Numbers

Problem Restatement We are given two arrays arr1 and arr2 representing two non-positive integers in base 10. Each array has -1 as the first element (sign) followed by the digits. We need to return the sum of the two numbers, also in the same format. The official constraints are similar to LeetCode 66 (Plus One) but for non-positive integers. Input and Output Item Meaning Input Two arrays representing negative integers...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1041: Robot Bounded In Circle

Problem Restatement A robot starts at the origin facing north and follows a sequence of instructions: 'G' : move one step forward. 'L' : turn left 90 degrees. 'R' : turn right 90 degrees. We need to determine if the robot stays within a bounded circle (i.e., the robot's path is bounded) when the instructions are repeated indefinitely. The official constraints state that 1 <= instructions.length <= 100 . Input...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1094: Car Pooling

Problem Restatement We have a car with capacity seats. We are given a list of trips: each trip [numPassengers, from, to] means numPassengers passengers board at from and alight at to . We need to return true if it is possible to pick up all passengers without exceeding capacity at any point. The official constraints state that 1 <= trips.length <= 1000 , 1 <= numPassengers <= 100 , and...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1001: Grid Illumination

Problem Restatement We have an n x n grid. We are given an array lamps , where each element is [row_i, col_i] , meaning a lamp is placed at that cell. A lamp illuminates its entire row, its entire column, its main diagonal, and its anti-diagonal. We are also given an array queries , where each query is [row_j, col_j] . For each query: If the queried cell is illuminated,...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 900: RLE Iterator

Problem Restatement We need to design an iterator over a run-length encoded sequence. The encoded array stores pairs: [count, value] At every even index i , encoding[i] is the number of times encoding[i + 1] appears in the decoded sequence. For example: encoding = [3, 8, 0, 9, 2, 5] represents: [8, 8, 8, 5, 5] because there are three 8 s, zero 9 s, and two 5 s. The...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 844: Backspace String Compare

Problem Restatement We are given two strings s and t . Each string contains lowercase letters and the character "#" . The "#" character acts like a backspace in a text editor. It deletes the character immediately before it. If there is no character before it, it does nothing. Return True if both strings become equal after applying all backspaces. Otherwise, return False . Input and Output Item Meaning Input...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 950: Reveal Cards In Increasing Order

Problem Restatement We are given an array: deck Each card has a unique integer. We may reorder the deck however we want. The first element of the returned array is considered the top of the deck. Then the reveal process works like this: Reveal the top card and remove it. If cards remain, move the next top card to the bottom. Repeat until all cards are revealed. Return an initial...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 999: Available Captures for Rook

Problem Restatement We are given an 8 x 8 chessboard. Each cell contains one of four characters: Character Meaning "R" White rook "B" White bishop "p" Black pawn "." Empty square There is exactly one rook. The rook can move horizontally or vertically. It can capture a pawn if the pawn is the first piece in that direction. The rook cannot move through another piece. A bishop blocks the rook,...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 874: Walking Robot Simulation

Problem Restatement A robot starts at: (0, 0) on an infinite XY-plane. It starts facing north. The robot receives commands: Command Meaning -2 Turn left 90 degrees -1 Turn right 90 degrees 1 to 9 Move forward that many units There are also obstacles on the grid. If the robot tries to move onto an obstacle, it stays in its current position and moves to the next command. Return the...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 824: Goat Latin

Problem Restatement We are given a sentence made of words separated by single spaces. Each word contains only uppercase and lowercase English letters. We need to convert every word into Goat Latin using these rules: If a word starts with a vowel, append "ma" . If a word starts with a consonant, move the first letter to the end, then append "ma" . Append 'a' characters based on the word...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 840: Magic Squares In Grid

Problem Restatement We are given a row x col grid of integers. We need to count how many contiguous 3 x 3 subgrids are magic squares. A 3 x 3 magic square must satisfy all of these rules: Rule Meaning Size The subgrid is exactly 3 x 3 Values It contains distinct numbers from 1 to 9 Rows Every row has the same sum Columns Every column has the same...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 946: Validate Stack Sequences

Problem Restatement We are given two integer arrays: pushed popped Both arrays contain the same distinct values. pushed gives the order in which values are pushed onto an initially empty stack. popped gives a possible order in which values are popped from the stack. Return True if popped could be produced by valid stack operations. Otherwise, return False . The official statement asks whether popped could result from a sequence...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 725: Split Linked List in Parts

Problem Restatement We are given the head of a singly linked list and an integer k . We need to split the linked list into k consecutive parts. The parts must follow these rules: Rule Meaning Keep original order Nodes must appear in the same order as the input list Sizes as equal as possible No two parts should differ in size by more than 1 Earlier parts are larger...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 799: Champagne Tower

Problem Restatement We stack glasses in a pyramid. The first row has 1 glass, the second row has 2 glasses, the third row has 3 glasses, and so on. Each glass can hold exactly 1 cup of champagne. We pour poured cups into the top glass. If a glass receives more than 1 cup, it keeps 1 cup and splits the extra champagne equally between the two glasses below it....

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 723: Candy Crush

Problem Restatement We are given an m x n board of candies. Each cell contains either: Value Meaning Positive integer A candy type 0 Empty cell The board represents the game state after a move. We need to repeatedly apply these rules until the board becomes stable: If three or more candies of the same type are adjacent horizontally or vertically, crush all of them at the same time. Crushed...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 722: Remove Comments

Problem Restatement We are given a C++ program as a list of strings: source Each string is one line of code. We need to remove two kinds of comments: Comment Type Meaning Line comment // Ignore // and everything after it on the same line Block comment /* ... */ Ignore everything from /* until the next non-overlapping */ After removing comments, return the remaining source code as a list...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 749: Contain Virus

Problem Restatement We are given a 2D grid representing infected and uninfected cells. Each cell is one of: Value Meaning 0 Uninfected 1 Infected -1 Quarantined infected region Every night: Each infected region spreads to neighboring uninfected cells. We may choose exactly one infected region to quarantine. Quarantining a region requires building walls along its border. A quarantined region no longer spreads. We always quarantine the region that would infect...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 867: Transpose Matrix

Problem Restatement We are given a 2D integer array matrix . We need to return its transpose. The transpose of a matrix is created by switching rows and columns. If an element is at: matrix[row][col] then in the transposed matrix it goes to: answer[col][row] So the value at row r , column c becomes the value at row c , column r . Input and Output Item Meaning Input A...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 941: Valid Mountain Array

Problem Restatement We are given an integer array arr . Return True if and only if arr is a valid mountain array. A valid mountain array must satisfy three rules: It has at least 3 elements. It strictly increases up to one peak. It strictly decreases after that peak. The peak cannot be the first element or the last element. The official statement defines a mountain array as one where...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 794: Valid Tic-Tac-Toe State

Problem Restatement We are given a Tic-Tac-Toe board as a list of three strings. Each cell contains one of: Character Meaning "X" First player's mark "O" Second player's mark " " Empty square We need to return True if this board position could happen during a valid Tic-Tac-Toe game. The rules are: X always moves first. Players alternate turns. A move can only be placed in an empty square. The...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 989: Add to Array-Form of Integer

Problem Restatement We are given an integer num in array form. That means each element of num is one digit, ordered from most significant to least significant. For example: num = [1, 3, 2, 1] represents: 1321 We are also given an integer k . We need to return the array-form of: num + k The official constraints include 1 <= num.length <= 10^4 , each digit is between 0...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 43: Multiply Strings

Problem Restatement We are given two non-negative integers num1 and num2 , but they are stored as strings. We need to return their product, also as a string. We cannot use a built-in big integer library, and we cannot directly convert the whole input strings into integers. The official problem states this string multiplication requirement and restriction directly. Example: num1 = "2" num2 = "3" The product is: "6" Another...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 622: Design Circular Queue

Problem Restatement We need to design a circular queue. A queue follows FIFO order: first in, first out. A circular queue uses a fixed-size array, but when the end of the array is reached, the next position wraps around to the beginning. This lets the queue reuse empty space created by earlier removals. The class must support these operations: Operation Meaning MyCircularQueue(k) Create a queue with capacity k enQueue(value) Insert...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 699: Falling Squares

Problem Restatement We are given a list of squares falling onto the X-axis. Each square is described by: [left, side_length] The square spans the interval: [left, left + side_length) The square falls vertically until: Situation Result It hits the ground Stops at height 0 It lands on another square Stacks on top After each square falls, we must report the maximum height among all squares so far. The official statement...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 649: Dota2 Senate

Problem Restatement We are given a string senate . Each character represents one senator: Character Party "R" Radiant "D" Dire The voting process happens in rounds from left to right. On a senator's turn, if they still have voting rights, they can ban one senator from the opposite party. A banned senator loses voting rights for the current and all future rounds. If all remaining senators with voting rights belong...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 985: Sum of Even Numbers After Queries

Problem Restatement We are given an integer array nums and an array queries . Each query has the form: [val, index] For each query, we update the array: nums[index] = nums[index] + val After that update, we need to record the sum of all even values in nums . Return an array where each element is the even-number sum after the corresponding query. Each query permanently changes nums . The...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 885: Spiral Matrix III

Problem Restatement We are given a grid with rows rows and cols columns. We start at cell: (rStart, cStart) Initially, we face east. We walk in a clockwise spiral until every grid cell has been visited. The walk may go outside the grid boundary, but we only record coordinates that are inside the grid. Return the grid coordinates in the order we visit them. LeetCode defines the northwest corner as...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 860: Lemonade Change

Problem Restatement Each lemonade costs $5 . Customers stand in a queue. Each customer buys exactly one lemonade and pays with one bill. The bill can be: 5, 10, or 20 We start with no money. For each customer, we must give the correct change immediately, using only bills received from earlier customers. Return True if we can give correct change to every customer. Otherwise, return False . Input and...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 735: Asteroid Collision

Problem Restatement We are given an integer array asteroids . Each integer represents one asteroid. The absolute value is the asteroid size. The sign is its direction: Value Direction Positive Moving right Negative Moving left All asteroids move at the same speed. When two asteroids collide: Case Result Smaller asteroid Explodes Same size Both explode Same direction They never collide We need to return the final state after all collisions....

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 957: Prison Cells After N Days

Problem Restatement We are given an array cells of length 8 . Each cell is either: 0 # vacant 1 # occupied Every day, the cells change using this rule: If a cell has two adjacent neighbors that are both occupied or both vacant, the cell becomes occupied. Otherwise, it becomes vacant. The first and last cells do not have two neighbors, so they always become vacant after one day....

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 833: Find And Replace in String

Problem Restatement We are given a string s and three arrays: Array Meaning indices Starting positions where replacement may happen sources Source strings that must match at those positions targets Replacement strings For each operation i , we check whether sources[i] appears in the original string s starting at index indices[i] . If it matches, we replace that source substring with targets[i] . If it does not match, we do...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 883: Projection Area of 3D Shapes

Problem Restatement We are given an n x n grid. Each cell: grid[r][c] contains a vertical stack of cubes. We want the total projection area of the 3D shape onto three planes: Projection Meaning Top view Looking down from above Front view Looking from the front Side view Looking from the side Return the sum of these three projection areas. The official problem defines each cube as a 1 x...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 832: Flipping an Image

Problem Restatement We are given an n x n binary matrix image . Each cell is either: Value Meaning 0 White pixel 1 Black pixel We need to do two operations: Flip the image horizontally. Invert the image. Flipping horizontally means reversing each row. For example: [1, 1, 0] -> [0, 1, 1] Inverting means changing every 0 to 1 and every 1 to 0 . For example: [0, 1,...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 640: Solve the Equation

Problem Restatement We are given a linear equation as a string. The equation contains: Token Meaning x The variable integers Constant terms or coefficients + and - Operations = Separates left and right sides We need to solve for x . Return one of three possible answers: Case Return Exactly one solution "x=#value" No solution "No solution" Infinite solutions "Infinite solutions" If there is exactly one solution, the problem guarantees...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 758: Bold Words in String

Problem Restatement We are given: words s words is a list of strings. s is the target string. We need to wrap substrings of s with: <b> ... </b> if those substrings match any word in words . There are two important rules: If two bold parts overlap, merge them into one bold section. If two bold parts are adjacent, merge them too. Return the final formatted string. Input and...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 636: Exclusive Time of Functions

Problem Restatement We are given n functions with IDs from 0 to n - 1 . We also receive a list of logs. Each log has this format: "{function_id}:{start_or_end}:{timestamp}" For example: "0:start:3" means function 0 starts at the beginning of timestamp 3 . "1:end:5" means function 1 ends at the end of timestamp 5 . The CPU is single-threaded, so only one function runs at a time. A function may...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 831: Masking Personal Information

Problem Restatement We are given a string s . The string represents either: Type Example Email address "LeetCode@LeetCode.com" Phone number "1(234)567-890" We need to return the masked version of the personal information. The masking rules are different for emails and phone numbers. An email contains the character "@" . A phone number contains digits and separator characters. Input and Output Item Meaning Input A personal information string s Output The...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 682: Baseball Game

Problem Restatement We are given a list of operations called ops . These operations describe scores in a baseball game. We process the operations from left to right and maintain a record of valid scores. The operations are: Operation Meaning Integer x Record a new score x "+" Record a score equal to the sum of the previous two valid scores "D" Record a score equal to double the previous...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 806: Number of Lines To Write String

Problem Restatement We are given a string s containing only lowercase English letters. We are also given an array widths of length 26 , where: widths[0] # width of 'a' widths[1] # width of 'b' widths[25] # width of 'z' Each line can contain at most 100 pixels. We write the characters of s from left to right. For each character, if it fits on the current line, we add...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 681: Next Closest Time

Problem Restatement We are given a valid time string in the format: HH:MM We need to form the next closest valid time by reusing only the digits that already appear in the input time. Each digit may be reused any number of times. For example, if the input is: time = "19:34" then the available digits are: 1, 9, 3, 4 We may use these digits repeatedly to form another...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 755: Pour Water

Problem Restatement We are given an elevation map as an integer array heights . The value heights[i] is the current height at index i . Each index has width 1 . We are also given: volume k volume units of water fall at index k , one unit at a time. Each unit of water follows these rules: It first tries to move left. If moving left can eventually make...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 855: Exam Room

Problem Restatement We need to design an ExamRoom class. There are n seats in one row, labeled: 0, 1, 2, ..., n - 1 When a student enters, they choose the seat that maximizes the distance to the closest occupied seat. If several seats give the same distance, the student chooses the smallest seat number. If the room is empty, the student sits at seat 0 . We need to...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 929: Unique Email Addresses

Problem Restatement We are given a list of email addresses. Each email has two parts: local-name@domain-name The problem defines two special rules that apply only to the local name. Rule 1: Ignore Dots In the local name: "." characters are ignored. For example: "alice.z" == "alicez" Rule 2: Ignore Everything After '+' If a plus sign appears in the local name: "+" then everything after it is ignored. For example:...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 928: Minimize Malware Spread II

Problem Restatement We are given an undirected graph with n nodes. The graph is represented as an adjacency matrix: graph[i][j] == 1 means node i is directly connected to node j . Some nodes are initially infected by malware. These nodes are listed in: initial Malware spreads through edges. If an infected node is connected to an uninfected node, the uninfected node also becomes infected. This continues until no more...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 661: Image Smoother

Problem Restatement We are given a grayscale image represented as a 2D integer matrix img . Each cell contains a pixel value. We must create a smoothed image. For every cell, compute the average of: The cell itself All valid neighboring cells Neighbors include all eight surrounding directions: top bottom left right top-left top-right bottom-left bottom-right The average is rounded down to the nearest integer. Cells outside the image boundaries...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 657: Robot Return to Origin

Problem Restatement A robot starts at position: (0, 0) We are given a string called moves . Each character tells the robot to move one step: Move Meaning U Move up D Move down L Move left R Move right After executing all moves, return True if the robot returns to the origin (0, 0) . Otherwise, return False . Input and Output Item Meaning Input A string moves Output...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 573: Squirrel Simulation

Problem Restatement We are given a garden grid with a tree, a squirrel, and several nuts. The squirrel must collect all nuts and put them under the tree one by one. The squirrel can carry at most one nut at a time. It can move one cell at a time in four directions: up, down, left, and right. Return the minimum total distance the squirrel must move. The problem gives...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 544: Output Contest Matches

Problem Restatement We are given n teams labeled from 1 to n . Team 1 is the strongest team. Team n is the weakest team. In each round, we pair the strongest remaining team with the weakest remaining team, the second strongest with the second weakest, and so on. We need to return the final tournament bracket as a string. Pairs are written using parentheses and commas: (a,b) The input...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 566: Reshape the Matrix

Problem Restatement We are given a matrix mat with m rows and n columns. We are also given two integers: Value Meaning r Desired number of rows c Desired number of columns We need to reshape the matrix into size r x c . The reshaped matrix must preserve the original row-traversing order. That means we read the original matrix from left to right, row by row, and place the...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 541: Reverse String II

Problem Restatement We are given a string s and an integer k . Starting from the beginning of the string, for every block of 2k characters, reverse the first k characters and leave the next k characters unchanged. There are two end cases: Remaining Characters Rule Fewer than k Reverse all remaining characters At least k but fewer than 2k Reverse the first k , leave the rest unchanged The...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 728: Self Dividing Numbers

Problem Restatement We are given two integers, left and right . We need to return all self-dividing numbers in the inclusive range: [left, right] A self-dividing number is divisible by every digit it contains. For example, 128 is self-dividing because: 128 % 1 == 0 128 % 2 == 0 128 % 8 == 0 A self-dividing number cannot contain the digit 0 , because division by zero is not...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 537: Complex Number Multiplication

Problem Restatement We are given two strings representing complex numbers. The format is: "real+imaginaryi" For example: "1+1i" represents: 1 + i We need to multiply the two complex numbers and return the result in the same string format. The imaginary unit satisfies: i^2 = -1 Input and Output Item Meaning Input Two strings representing complex numbers Output Their product as a complex-number string Format "a+bi" Values Integers, possibly negative Function...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 551: Student Attendance Record I

Problem Restatement We are given a string s representing one student's attendance record. Each character has one meaning: Character Meaning "A" Absent "L" Late "P" Present The student gets an attendance award only if both rules are satisfied: The student has strictly fewer than 2 absences in total. The student is never late for 3 or more consecutive days. Return true if the student can receive the award. Otherwise, return...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 422: Valid Word Square

Problem Restatement We are given an array of strings: words Return True if the strings form a valid word square. A word square means: row k == column k for every valid index k . The words may have different lengths, so we must be careful with missing characters. The source statement defines a valid word square as a sequence where the k th row and k th column read...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 498: Diagonal Traverse

Problem Restatement We are given an m x n matrix mat . We need to return all elements of the matrix in diagonal order. The traversal starts at the top-left cell, then moves along diagonals in alternating directions. For this matrix: mat = [ [1, 2, 3], [4, 5, 6], [7, 8, 9], ] The diagonal order is: [1, 2, 4, 7, 5, 3, 6, 8, 9] The official problem...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 495: Teemo Attacking

Problem Restatement Teemo attacks Ashe multiple times. We are given: Input Meaning timeSeries Times when Teemo attacks duration Poison duration after one attack When Ashe is poisoned, the poison lasts for exactly duration seconds. If another attack happens before the poison ends, the poison timer resets and continues from the new attack time. We need to return the total number of seconds Ashe is poisoned. Input and Output Item Meaning...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 468: Validate IP Address

Problem Restatement We are given a string queryIP . We need to return one of three strings: "IPv4" "IPv6" "Neither" Return "IPv4" if the string is a valid IPv4 address. Return "IPv6" if the string is a valid IPv6 address. Otherwise, return "Neither" . A valid IPv4 address has four decimal parts separated by dots. Each part must be between 0 and 255 , and leading zeros are not allowed....

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 418: Sentence Screen Fitting

Problem Restatement We are given: Value Meaning sentence A list of words rows Number of screen rows cols Number of columns per row We want to place the sentence repeatedly on the screen. Rules: Words must appear in the original order. A word cannot be split across lines. Consecutive words are separated by one space. The sentence repeats cyclically. Return how many complete times the sentence fits on the screen....

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 466: Count The Repetitions

Problem Restatement We are given two strings and two repetition counts: s1, n1 s2, n2 The notation [s, n] means string s repeated n times. For example: ["abc", 3] = "abcabcabc" Define: str1 = [s1, n1] str2 = [s2, n2] We need to find the maximum integer m such that: [str2, m] can be obtained from str1 by deleting some characters. In other words, we need to count how many...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 415: Add Strings

Problem Restatement We are given two non-negative integers as strings: num1 num2 Return their sum as a string. We cannot use a built-in big integer library. We also cannot directly convert the whole input strings into integers. So this is manual addition, the same way we add numbers on paper. The source problem states that num1 and num2 contain only digits, have no leading zeroes except "0" itself, and each...

Practice › LeetCode › LeetCode (archived) › LeetCode 03xx ›

LeetCode 390: Elimination Game

Problem Restatement We start with a sorted list of integers: [1, 2, 3, ..., n] Then we repeatedly remove numbers until only one number remains. The removal process alternates direction: From left to right, remove the first number and every other number after it. From right to left, remove the rightmost number and every other number before it. Keep alternating directions. Return the last remaining number. For example, when n...

Practice › LeetCode › LeetCode (archived) › LeetCode 02xx ›

LeetCode 293: Flip Game

Problem Restatement We are given a string currentState containing only two characters: "+" "-" A valid move means choosing two consecutive plus signs: "++" and flipping them into: "--" We need to return all possible states of the string after making exactly one valid move. The answer may be returned in any order. If there is no valid move, return an empty list. The source statement defines the game this...

Practice › LeetCode › LeetCode (archived) › LeetCode 02xx ›

LeetCode 289: Game of Life

Problem Restatement We are given an m x n board. Each cell is either: Value Meaning 0 Dead cell 1 Live cell Each cell has up to eight neighbors: horizontal vertical diagonal The next board state is computed using these rules: Current State Live Neighbors Next State Live Fewer than 2 Dead Live 2 or 3 Live Live More than 3 Dead Dead Exactly 3 Live All cells must update...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 68: Text Justification

Problem Restatement We are given a list of words and an integer maxWidth . We need to format the words into lines of exactly maxWidth characters. The rules are: Pack as many words as possible into each line. Each line must have exactly maxWidth characters. For normal lines, spaces should be distributed as evenly as possible between words. If spaces cannot divide evenly, the left gaps get more spaces than...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 67: Add Binary

Problem Restatement We are given two binary strings, a and b . Each string contains only characters "0" and "1" . We need to return their sum as a binary string. The official constraints are 1 <= a.length, b.length <= 10^4 , both strings contain only binary digits, and neither string has leading zeroes except the string "0" itself. Input and Output Item Meaning Input Two binary strings a and...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 412: Fizz Buzz

Problem Restatement We are given an integer n . Return a string array answer of length n . For every integer i from 1 to n : Condition Output i is divisible by both 3 and 5 "FizzBuzz" i is divisible by 3 "Fizz" i is divisible by 5 "Buzz" None of the above i as a string The array is 1-indexed in the problem description, meaning answer[i] describes the...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 489: Robot Room Cleaner

Problem Restatement We control a robot cleaner inside a room modeled as a grid. Each cell is either: Value Meaning 1 Open cell 0 Blocked cell But the algorithm does not receive the grid directly. Instead, we only control the robot through four APIs: robot.move() robot.turnLeft() robot.turnRight() robot.clean() The robot starts at an unknown open cell and initially faces up. The room boundary is surrounded by walls. All open cells...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 463: Island Perimeter

Problem Restatement We are given a rectangular grid. Each cell is either: 1 # land 0 # water The grid contains exactly one island. Land cells connect horizontally or vertically, not diagonally. The grid is surrounded by water, and the island has no lakes. We need to return the perimeter of the island. A land cell is a square with side length 1 . So one isolated land cell has...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 38: Count and Say

Problem Restatement We are given a positive integer n . We need to return the n th term of the count-and-say sequence. The sequence starts with: countAndSay(1) = "1" For every n > 1 , the next term is built by reading the previous term using run-length encoding. Run-length encoding means grouping consecutive equal digits, then writing: count + digit For example: "111221" has groups: "111", "22", "1" So it...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 163: Missing Ranges

Problem Restatement We are given an inclusive range: [lower, upper] We are also given a sorted array nums . The array contains unique integers, and every number in nums lies inside [lower, upper] . A number is missing if it is inside [lower, upper] but does not appear in nums . We need to return the shortest sorted list of ranges that exactly covers all missing numbers. Each range is...

Practice › LeetCode › LeetCode (archived) › LeetCode 03xx ›

LeetCode 311: Sparse Matrix Multiplication

Problem Restatement We are given two sparse matrices mat1 and mat2 . A sparse matrix contains many zero values. We need to return the matrix product: mat1 * mat2 If mat1 has size m x k , and mat2 has size k x n , then the result has size m x n . For each result cell: answer[i][j] we compute the dot product of row i from mat1 and...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 408: Valid Word Abbreviation

Problem Restatement We are given a word and an abbreviation. The abbreviation may contain lowercase letters and digits. A digit sequence means we skip that many characters in the original word. We must return whether the abbreviation correctly represents the word. Numbers cannot have leading zeroes. For example, "01" is invalid. The official problem describes abbreviations as replacing non-adjacent, non-empty substrings with their lengths. It gives examples such as "s10n"...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 485: Max Consecutive Ones

Problem Restatement We are given a binary array nums . A binary array contains only: Value Meaning 0 Breaks a streak 1 Continues a streak We need to return the maximum number of consecutive 1 s in the array. The official problem statement asks for the maximum number of consecutive 1 s in a binary array. Input and Output Item Meaning Input A binary integer array nums Output Length of...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 59: Spiral Matrix II

Problem Restatement We are given a positive integer n . We need to generate an n x n matrix filled with numbers from 1 to n^2 in spiral order. The spiral starts at the top-left cell and moves: Right Down Left Up Then it repeats inward until every cell is filled. The official constraint is 1 <= n <= 20 . Input and Output Item Meaning Input A positive integer...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 434: Number of Segments in a String

Problem Restatement We are given a string s . A segment is a contiguous sequence of non-space characters. We need to count how many segments appear in the string. For example: s = "Hello, my name is John" contains these segments: "Hello," "my" "name" "is" "John" So the answer is: 5 The official problem defines a segment as a contiguous sequence of non-space characters. The string may contain leading spaces,...

Practice › LeetCode › LeetCode (archived) › LeetCode 02xx ›

LeetCode 258: Add Digits

Problem Restatement We are given a non-negative integer num . Repeatedly add all of its digits until the result has only one digit. Return that final one-digit number. Example: num = 38 First add its digits: 3 + 8 = 11 The result still has two digits, so add again: 1 + 1 = 2 Now the result has one digit. Answer: 2 The follow-up asks for an O(1) solution...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 482: License Key Formatting

Problem Restatement We are given a string s representing a license key and an integer k . The string contains letters, digits, and dashes. We need to reformat it so that: Rule Meaning Remove old dashes Existing dashes do not matter Convert letters All letters become uppercase Regroup characters Groups are separated by dashes Group size Every group has exactly k characters, except maybe the first First group It may...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 158: Read N Characters Given read4 II - Call Multiple Times

Problem Restatement We are given a file, but we cannot read from it directly. The only available API is: read4(buf4) This reads up to 4 characters from the file into buf4 , then returns how many characters were actually read. We need to implement: read(buf, n) It should read up to n characters, write them into buf , and return the number of characters actually read. The difference from LeetCode...

Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 481: Magical String

Problem Restatement We are given an integer n . There is a special infinite string s made only of characters '1' and '2' . The first part of the string is: 1221121221221121122... This string is called magical because if we group equal consecutive characters, the group lengths form the same string again. For example: s = 1 22 11 2 1 22 1 22 11 2 11 22 ... length...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 157: Read N Characters Given Read4

Problem Restatement We are given a file, but we cannot access the file directly. The only way to read from the file is through a provided API: read4(buf4) This function reads up to 4 characters from the file and writes them into buf4 . It returns the actual number of characters read. We need to implement: read(buf, n) This function should read up to n characters from the file, write...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 54: Spiral Matrix

Problem Restatement We are given an m x n matrix. We need to return all elements of the matrix in spiral order. The spiral starts at the top-left cell. It moves: Right across the top row Down the right column Left across the bottom row Up the left column Then it repeats the same pattern on the inner part of the matrix. The official constraints are 1 <= m, n...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 8: String to Integer (atoi)

Problem Restatement We are given a string s . We need to implement myAtoi(s) , which converts the beginning of the string into a signed 32-bit integer. The parsing follows these rules: Ignore leading spaces. Read an optional sign, either + or - . Read digits until a non-digit character appears. If no digits are read, return 0 . Clamp the result into the signed 32-bit integer range. The signed...

Practice › LeetCode › LeetCode (archived) › LeetCode 00xx ›

LeetCode 6: Zigzag Conversion

Problem Restatement We are given: a string s an integer numRows We write the characters of the string in a zigzag pattern across multiple rows. Then we read the rows from top to bottom. The result is a new string. The official LeetCode statement uses this example: PAYPALISHIRING with: numRows = 3 becomes: P A H N A P L S I I G Y I R Reading row by...

Maths › 03. Logic and Foundations ›

11.3 Universal Machines

11.3 Universal Machines A universal Turing machine is a Turing machine that can simulate other Turing machines. This is one of the most important ideas in computability theory. It means that computation can be represented as data. A machine can be written down, encoded as a string, and given as input to another machine. In ordinary programming terms, a universal machine is like an interpreter. It receives two things: $$...

#simulation

LeetCode 3616 - Number of Student Replacements

LeetCode 3792 - Sum of Increasing Product Blocks

LeetCode 3867 - Sum of GCD of Formed Pairs

LeetCode 3775 - Reverse Words With Same Vowel Count

LeetCode 3847 - Find the Score Difference in a Game

LeetCode 3842 - Toggle Light Bulbs

LeetCode 3838 - Weighted Word Mapping

LeetCode 3834 - Merge Adjacent Equal Elements

LeetCode 3823 - Reverse Letters Then Special Characters in a String

LeetCode 3819 - Rotate Non Negative Elements

LeetCode 3813 - Vowel-Consonant Score

LeetCode 3703 - Remove K-Balanced Substrings

LeetCode 3679 - Minimum Discards to Balance Inventory

LeetCode 3522 - Calculate Score After Performing Instructions

LeetCode 3412 - Find Mirror Score of a String

LeetCode 3726 - Remove Zeros in Decimal Representation

LeetCode 3688 - Bitwise OR of Even Numbers in an Array

LeetCode 3653 - XOR After Range Multiplication Queries I

LeetCode 3612 - Process String with Special Operations I

LeetCode 3614 - Process String with Special Operations II

LeetCode 3597 - Partition String

LeetCode 3582 - Generate Tag for Video Caption

LeetCode 3561 - Resulting String After Adjacent Removals

LeetCode 3510 - Minimum Pair Removal to Sort Array II

LeetCode 3507 - Minimum Pair Removal to Sort Array I

LeetCode 3498 - Reverse Degree of a String

LeetCode 3494 - Find the Minimum Amount of Time to Brew Potions

LeetCode 3477 - Fruits Into Baskets II

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

LeetCode 3433 - Count Mentions Per User

LeetCode 3417 - Zigzag Grid Traversal With Skip

LeetCode 3687 - Library Late Fee Calculator

LeetCode 3360 - Stone Removal Game

LeetCode 2739 - Total Distance Traveled

LeetCode 2243 - Calculate Digit Sum of a String

LeetCode 2180 - Count Integers With Even Digit Sum

LeetCode 3100 - Water Bottles II

LeetCode 2352 - Equal Row and Column Pairs

LeetCode 2056 - Number of Valid Move Combinations On Chessboard

LeetCode 2079 - Watering Plants

LeetCode 2365 - Task Scheduler II

LeetCode 2043 - Simple Bank System

LeetCode 3175 - Find The First Player to win K Games in a Row

LeetCode 1945 - Sum of Digits of String After Convert

LeetCode 3066 - Minimum Operations to Exceed Threshold Value II

LeetCode 2177 - Find Three Consecutive Integers That Sum to a Given Number

LeetCode 3354 - Make Array Elements Equal to Zero

LeetCode 1860 - Incremental Memory Leak

LeetCode 2696 - Minimum String Length After Removing Substrings

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

LeetCode 2596 - Check Knight Tour Configuration

LeetCode 2221 - Find Triangular Sum of an Array

LeetCode 2682 - Find the Losers of the Circular Game

LeetCode 2553 - Separate the Digits in an Array

LeetCode 2534 - Time Taken to Cross the Door

LeetCode 3069 - Distribute Elements Into Two Arrays I

LeetCode 3266 - Final Array State After K Multiplication Operations II

LeetCode 3248 - Snake in Matrix

LeetCode 1929 - Concatenation of Array

LeetCode 1910 - Remove All Occurrences of a Substring

LeetCode 2960 - Count Tested Devices After Test Operations

LeetCode 2357 - Make Array Zero by Subtracting Equal Amounts

LeetCode 2161 - Partition Array According to Given Pivot

LeetCode 2482 - Difference Between Ones and Zeros in Row and Column

LeetCode 3160 - Find the Number of Distinct Colors Among the Balls

LeetCode 2303 - Calculate Amount Paid in Taxes

LeetCode 2390 - Removing Stars From a String

LeetCode 3264 - Final Array State After K Multiplication Operations I

LeetCode 2211 - Count Collisions on a Road

LeetCode 2069 - Walking Robot Simulation II

LeetCode 2022 - Convert 1D Array Into 2D Array

LeetCode 2061 - Number of Spaces Cleaning Robot Cleaned

LeetCode 3324 - Find the Sequence of Strings Appeared on the Screen

LeetCode 2562 - Find the Array Concatenation Value

LeetCode 2507 - Smallest Value After Replacing With Sum of Prime Factors

LeetCode 2751 - Robot Collisions

LeetCode 2289 - Steps to Make Array Non-decreasing

LeetCode 2679 - Sum in a Matrix

LeetCode 3271 - Hash Divided String