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Practice › LeetCode › LeetCode 38xx ›

LeetCode 3890 - Integers With Multiple Sum of Two Cubes

LeetCode Problem 3890 Difficulty: 🟡 Medium Topics: Hash Table, Sorting, Counting, Enumeration Solution Problem Understanding The problem asks us to find all integers x less than or equal to a given integer n such that x can be expressed as the sum of cubes of two positive integers in at least two distinct ways . A “distinct way” means that the pairs (a, b) used to form x are different,...
leetcode Medium hash-table sorting counting enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3880 - Minimum Absolute Difference Between Two Values

LeetCode Problem 3880 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 3880 - Minimum Absolute Difference Between Two Values Problem Understanding The problem gives us an integer array nums where every element is guaranteed to be one of three values: 0 , 1 , or 2 . A pair of indices (i, j) is considered valid when: nums[i] == 1 nums[j] == 2 For every valid pair, we compute the...
leetcode Easy array enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3784 - Minimum Deletion Cost to Make All Characters Equal

LeetCode Problem 3784 Difficulty: 🟡 Medium Topics: Array, Hash Table, String, Enumeration Solution Problem Understanding The problem asks us to minimize the total cost of deleting characters from a string such that the resulting string contains only one unique character . We are given a string s of length n and an array cost of the same length, where cost[i] is the cost of deleting the character s[i] . The...
leetcode Medium array hash-table string enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3872 - Longest Arithmetic Sequence After Changing At Most One Element

LeetCode Problem 3872 Difficulty: 🟡 Medium Topics: Array, Enumeration Solution Problem Understanding The problem requires us to find the longest arithmetic subarray from a given array of integers nums if we are allowed to modify at most one element. An arithmetic subarray is a contiguous sequence in which the difference between consecutive elements is constant. The input, nums , is an integer array of length between 4 and 105, and...
leetcode Medium array enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3833 - Count Dominant Indices

LeetCode Problem 3833 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 3833 - Count Dominant Indices Problem Understanding The problem gives us an integer array nums of length n . For every index i , we must determine whether the element nums[i] is dominant . An index is considered dominant if its value is strictly greater than the average of all elements to its right. In other words, for index...
leetcode Easy array enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3830 - Longest Alternating Subarray After Removing At Most One Element

LeetCode Problem 3830 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Enumeration Solution Problem Understanding The problem asks us to find the longest alternating subarray in a given integer array nums , where a subarray is defined as consecutive elements. A subarray is considered alternating if the sequence of comparisons between adjacent elements strictly alternates between less-than and greater-than. Formally, for a subarray nums[l..r] , it must satisfy either: nums[l] <...
leetcode Hard array dynamic-programming enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3827 - Count Monobit Integers

LeetCode Problem 3827 Difficulty: 🟢 Easy Topics: Bit Manipulation, Enumeration Solution Problem Understanding The problem asks us to count Monobit integers from 0 to n . A Monobit integer is one where all bits in its binary representation are the same. This means there are only two possibilities for a valid Monobit integer: all zeros or all ones. For instance, 0 ( 0b0 ), 1 ( 0b1 ), 3 (...
leetcode Easy bit-manipulation enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3825 - Longest Strictly Increasing Subsequence With Non-Zero Bitwise AND

LeetCode Problem 3825 Difficulty: 🟡 Medium Topics: Array, Binary Search, Bit Manipulation, Enumeration Solution Problem Understanding This problem asks us to find the longest strictly increasing subsequence (LIS) in a given integer array nums , with the additional constraint that the bitwise AND of all elements in the subsequence must be non-zero . In simpler terms, among all sequences you can extract from nums where each number is strictly larger...
leetcode Medium array binary-search bit-manipulation enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3722 - Lexicographically Smallest String After Reverse

LeetCode Problem 3722 Difficulty: 🟡 Medium Topics: Two Pointers, Binary Search, Enumeration Solution Problem Understanding The problem asks us to find the lexicographically smallest string after performing exactly one reverse operation on a contiguous prefix or suffix of a given string s . The string consists only of lowercase English letters and can have a length up to 1000 characters. In other words, we can either reverse the first k...
leetcode Medium two-pointers binary-search enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3720 - Lexicographically Smallest Permutation Greater Than Target

LeetCode Problem 3720 Difficulty: 🟡 Medium Topics: Hash Table, String, Greedy, Counting, Enumeration Solution Before I write the full guide, I want to verify one important detail: LeetCode 3720 appears to be a very recent problem , and the exact intended optimal approach depends on the precise judge behavior and hidden constraints. Please confirm that the problem title and statement are exactly: LeetCode 3720 - Lexicographically Smallest Permutation Greater Than...
leetcode Medium hash-table string greedy counting enumeration May 30, 2026
Practice › LeetCode › LeetCode 38xx ›

LeetCode 3804 - Number of Centered Subarrays

LeetCode Problem 3804 Difficulty: 🟡 Medium Topics: Array, Hash Table, Enumeration Solution Problem Understanding The problem asks us to count the number of centered subarrays in a given integer array nums . A subarray is called centered if the sum of its elements is equal to at least one element within that subarray . In simpler terms, for every contiguous sequence of numbers in nums , we need to check...
leetcode Medium array hash-table enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3799 - Word Squares II

LeetCode Problem 3799 Difficulty: 🟡 Medium Topics: Array, String, Backtracking, Sorting, Enumeration Solution LeetCode 3799 - Word Squares II Problem Understanding We are given an array of distinct 4-letter words. Our goal is to construct every valid word square consisting of exactly four different words: top forms the top row. bottom forms the bottom row. left forms the left column. right forms the right column. Since each word has length...
leetcode Medium array string backtracking sorting enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3765 - Complete Prime Number

LeetCode Problem 3765 Difficulty: 🟡 Medium Topics: Math, Enumeration, Number Theory Solution LeetCode 3765 - Complete Prime Number Problem Understanding The problem gives us a positive integer num and asks whether it is a Complete Prime Number . A number qualifies as a Complete Prime Number if every prefix and every suffix of its decimal representation is prime. For a number with digits d1 d2 d3 ... dn : Prefixes...
leetcode Medium math enumeration number-theory May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3548 - Equal Sum Grid Partition II

LeetCode Problem 3548 Difficulty: 🔴 Hard Topics: Array, Hash Table, Matrix, Enumeration, Prefix Sum Solution Problem Understanding The problem asks us to determine if we can partition a given m x n grid of positive integers into two connected sections by making exactly one horizontal or vertical cut , such that the sums of the two sections are equal or can be made equal by removing at most one cell....
leetcode Hard array hash-table matrix enumeration prefix-sum May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3566 - Partition Array into Two Equal Product Subsets

LeetCode Problem 3566 Difficulty: 🟡 Medium Topics: Array, Bit Manipulation, Recursion, Enumeration Solution Here’s a detailed technical solution guide for LeetCode 3566 following your formatting rules: Problem Understanding The problem asks us to determine whether a given array of distinct positive integers can be split into two non-empty, disjoint subsets , such that the product of the elements in each subset equals a given target value . Each element of...
leetcode Medium array bit-manipulation recursion enumeration May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3445 - Maximum Difference Between Even and Odd Frequency II

LeetCode Problem 3445 Difficulty: 🔴 Hard Topics: String, Sliding Window, Enumeration, Prefix Sum Solution LeetCode 3445 - Maximum Difference Between Even and Odd Frequency II Problem Understanding We are given a string s consisting only of digits '0' through '4' , and an integer k . For any substring subs whose length is at least k , we may choose two characters: Character a must appear an odd number of...
leetcode Hard string sliding-window enumeration prefix-sum May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3751 - Total Waviness of Numbers in Range I

LeetCode Problem 3751 Difficulty: 🟡 Medium Topics: Math, Dynamic Programming, Enumeration Solution LeetCode 3751 - Total Waviness of Numbers in Range I Problem Understanding This problem asks us to compute the total waviness of every integer in an inclusive range [num1, num2] . For a single number, waviness is defined as the number of digits that are either peaks or valleys. A digit is a peak if it is strictly...
leetcode Medium math dynamic-programming enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3745 - Maximize Expression of Three Elements

LeetCode Problem 3745 Difficulty: 🟢 Easy Topics: Array, Greedy, Sorting, Enumeration Solution LeetCode 3745 - Maximize Expression of Three Elements Problem Understanding The problem gives us an integer array nums and asks us to choose three elements a , b , and c from distinct indices such that the expression: $$a + b - c$$ is as large as possible. The important detail is that the three elements must come...
leetcode Easy array greedy sorting enumeration May 30, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3734 - Lexicographically Smallest Palindromic Permutation Greater Than Target

LeetCode Problem 3734 Difficulty: 🔴 Hard Topics: Two Pointers, String, Enumeration Solution Problem Understanding We are given two strings, s and target , of the same length n . The goal is to rearrange the characters of s into a palindrome and then choose, among all possible palindromic permutations, the lexicographically smallest one that is strictly greater than target . A string a is lexicographically greater than a string b...
leetcode Hard two-pointers string enumeration May 30, 2026
Practice › LeetCode › LeetCode 36xx ›

LeetCode 3664 - Two-Letter Card Game

LeetCode Problem 3664 Difficulty: 🟡 Medium Topics: Array, Hash Table, String, Counting, Enumeration Solution Problem Understanding Each card consists of exactly two lowercase letters. A card is only relevant if it contains the given letter x somewhere in its two positions. During the game, we repeatedly select two cards that satisfy two conditions: Both cards contain the letter x . The two strings differ in exactly one position. After selecting...
leetcode Medium array hash-table string counting enumeration May 30, 2026
Practice › LeetCode › LeetCode 36xx ›

LeetCode 3630 - Partition Array for Maximum XOR and AND

LeetCode Problem 3630 Difficulty: 🔴 Hard Topics: Array, Math, Greedy, Bit Manipulation, Enumeration Solution Problem Understanding The problem asks us to partition an integer array nums into three subsequences A , B , and C such that every element belongs to exactly one subsequence. The goal is to maximize the sum XOR(A) + AND(B) + XOR(C) , where XOR and AND represent the bitwise XOR and AND of the elements...
leetcode Hard array math greedy bit-manipulation enumeration May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3588 - Find Maximum Area of a Triangle

LeetCode Problem 3588 Difficulty: 🟡 Medium Topics: Array, Hash Table, Math, Greedy, Geometry, Enumeration Solution LeetCode 3588 - Find Maximum Area of a Triangle Problem Understanding We are given n distinct points on a 2D Cartesian plane. Each point is represented as [x, y] . We must choose any three points that form a non-degenerate triangle, meaning the area must be strictly greater than zero. Among all valid triangles, we...
leetcode Medium array hash-table math greedy geometry enumeration May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3574 - Maximize Subarray GCD Score

LeetCode Problem 3574 Difficulty: 🔴 Hard Topics: Array, Math, Enumeration, Number Theory Solution Problem Understanding The problem asks us to choose a contiguous subarray from an array of positive integers after performing at most k doubling operations, where each element can be doubled at most once. After applying these optional doublings, we compute the score of a subarray as the product of its length and the greatest common divisor (GCD)...
leetcode Hard array math enumeration number-theory May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3546 - Equal Sum Grid Partition I

LeetCode Problem 3546 Difficulty: 🟡 Medium Topics: Array, Matrix, Enumeration, Prefix Sum Solution LeetCode 3546 - Equal Sum Grid Partition I Problem Understanding This problem asks us to determine whether a rectangular grid of positive integers can be split into two parts with exactly the same sum using a single straight cut. The cut can be made in only one of two ways: A horizontal cut between two adjacent rows....
leetcode Medium array matrix enumeration prefix-sum May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3514 - Number of Unique XOR Triplets II

LeetCode Problem 3514 Difficulty: 🟡 Medium Topics: Array, Math, Bit Manipulation, Enumeration Solution LeetCode 3514 - Number of Unique XOR Triplets II Problem Understanding We are given an integer array nums , and we must consider every triplet of indices (i, j, k) such that i <= j <= k . For each valid triplet, we compute: $$nums[i] \oplus nums[j] \oplus nums[k]$$ where ⊕ denotes the bitwise XOR operation. The...
leetcode Medium array math bit-manipulation enumeration May 30, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3503 - Longest Palindrome After Substring Concatenation I

LeetCode Problem 3503 Difficulty: 🟡 Medium Topics: Two Pointers, String, Dynamic Programming, Enumeration Solution LeetCode 3503 - Longest Palindrome After Substring Concatenation I Problem Understanding We are given two strings, s and t , and we are allowed to choose: Any substring of s , including the empty string. Any substring of t , including the empty string. The chosen substring from s must come first, and the chosen substring...
leetcode Medium two-pointers string dynamic-programming enumeration May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3499 - Maximize Active Section with Trade I

LeetCode Problem 3499 Difficulty: 🟡 Medium Topics: String, Enumeration Solution Problem Understanding The problem gives a binary string s representing sections of a system, where '1' indicates an active section and '0' indicates an inactive section. We are allowed at most one trade to maximize the number of active sections. A trade consists of two operations applied sequentially on the string: Convert a contiguous block of '1' s surrounded by...
leetcode Medium string enumeration May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3480 - Maximize Subarrays After Removing One Conflicting Pair

LeetCode Problem 3480 Difficulty: 🔴 Hard Topics: Array, Segment Tree, Enumeration, Prefix Sum Solution Here’s a detailed technical solution guide following your requested format for LeetCode 3480 - Maximize Subarrays After Removing One Conflicting Pair . Problem Understanding The problem gives you an integer n , which defines a sorted array nums = [1, 2, ..., n] . You are also given a list of conflictingPairs , each representing two...
leetcode Hard array segment-tree enumeration prefix-sum May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3470 - Permutations IV

LeetCode Problem 3470 Difficulty: 🔴 Hard Topics: Array, Math, Combinatorics, Enumeration Solution LeetCode 3470 - Permutations IV Problem Understanding We are given two integers, n and k . We must consider all permutations of the numbers 1 through n that satisfy an alternating parity condition. In a valid permutation, every pair of adjacent elements must have different parity. In other words: Odd must be followed by even. Even must be...
leetcode Hard array math combinatorics enumeration May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3440 - Reschedule Meetings for Maximum Free Time II

LeetCode Problem 3440 Difficulty: 🟡 Medium Topics: Array, Greedy, Enumeration Solution LeetCode 3440 - Reschedule Meetings for Maximum Free Time II Problem Understanding We are given an event that lasts from time 0 to eventTime . Inside this event there are n non-overlapping meetings, represented by the arrays startTime and endTime . The meeting at index i occupies the interval: [startTime[i], endTime[i]] The meetings are already sorted and non-overlapping, meaning:...
leetcode Medium array greedy enumeration May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3435 - Frequencies of Shortest Supersequences

LeetCode Problem 3435 Difficulty: 🔴 Hard Topics: Array, String, Bit Manipulation, Graph Theory, Topological Sort, Enumeration Solution Problem Understanding The problem asks us to find all shortest common supersequences (SCS) of a given list of two-character strings words . A shortest common supersequence is a string of minimum length that contains each word in words as a subsequence. Importantly, the output should not include SCSs that are permutations of each...
leetcode Hard array string bit-manipulation graph-theory topological-sort enumeration May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3411 - Maximum Subarray With Equal Products

LeetCode Problem 3411 Difficulty: 🟢 Easy Topics: Array, Math, Sliding Window, Enumeration, Number Theory Solution LeetCode 3411 - Maximum Subarray With Equal Products Problem Understanding We are given an array nums consisting of positive integers. For any array arr , define: prod(arr) as the product of all elements. gcd(arr) as the greatest common divisor of all elements. lcm(arr) as the least common multiple of all elements. A subarray is called...
leetcode Easy array math sliding-window enumeration number-theory May 30, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3403 - Find the Lexicographically Largest String From the Box I

LeetCode Problem 3403 Difficulty: 🟡 Medium Topics: Two Pointers, String, Enumeration Solution LeetCode 3403 - Find the Lexicographically Largest String From the Box I Problem Understanding We are given a string word of length n and an integer numFriends . In each round, the string is split into exactly numFriends non-empty contiguous pieces. Every distinct way to place the numFriends - 1 cuts is considered a different round. After each...
leetcode Medium two-pointers string enumeration May 30, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3025 - Find the Number of Ways to Place People I

LeetCode Problem 3025 Difficulty: 🟡 Medium Topics: Array, Math, Geometry, Sorting, Enumeration Solution Problem Understanding The problem gives us a list of distinct points on a 2D plane. Each point is represented as [x, y] , where x is the horizontal coordinate and y is the vertical coordinate. We must count how many ordered pairs (A, B) satisfy two conditions: Point A is on the upper-left side of point B...
leetcode Medium array math geometry sorting enumeration May 29, 2026
Practice › LeetCode › LeetCode 34xx ›

LeetCode 3404 - Count Special Subsequences

LeetCode Problem 3404 Difficulty: 🟡 Medium Topics: Array, Hash Table, Math, Enumeration Solution Problem Understanding This problem asks us to count the number of special subsequences of length four in a given array nums of positive integers. A special subsequence (p, q, r, s) must satisfy two requirements. First, the product of the first and third elements must equal the product of the second and fourth elements: nums[p] * nums[r]...
leetcode Medium array hash-table math enumeration May 29, 2026
Practice › LeetCode › LeetCode 32xx ›

LeetCode 3267 - Count Almost Equal Pairs II

LeetCode Problem 3267 Difficulty: 🔴 Hard Topics: Array, Hash Table, Sorting, Counting, Enumeration Solution LeetCode 3267 - Count Almost Equal Pairs II Problem Understanding We are given an array nums containing positive integers. We need to count how many pairs of indices (i, j) with i < j satisfy a special condition called almost equal . Two numbers x and y are considered almost equal if we can make them...
leetcode Hard array hash-table sorting counting enumeration May 29, 2026
Practice › LeetCode › LeetCode 27xx ›

LeetCode 2768 - Number of Black Blocks

LeetCode Problem 2768 Difficulty: 🟡 Medium Topics: Array, Hash Table, Enumeration Solution Problem Understanding This problem asks us to count the number of 2 x 2 blocks in a grid based on how many black cells they contain. We are given the dimensions of a grid, m rows and n columns, and a list of coordinates representing black cells. Every cell not listed is white. A block is a 2...
leetcode Medium array hash-table enumeration May 29, 2026
Practice › LeetCode › LeetCode 20xx ›

LeetCode 2094 - Finding 3-Digit Even Numbers

LeetCode Problem 2094 Difficulty: 🟢 Easy Topics: Array, Hash Table, Recursion, Sorting, Enumeration Solution Problem Understanding The problem gives us an array named digits , where every element is a single decimal digit from 0 to 9 . We must use exactly three elements from this array to build valid three digit integers. The important detail is that each digit can only be used as many times as it appears...
leetcode Easy array hash-table recursion sorting enumeration May 29, 2026
Practice › LeetCode › LeetCode 21xx ›

LeetCode 2162 - Minimum Cost to Set Cooking Time

LeetCode Problem 2162 Difficulty: 🟡 Medium Topics: Math, Enumeration Solution Problem Understanding This problem asks us to simulate the process of entering a cooking time into a microwave while minimizing the total finger movement and button pressing cost. The microwave accepts at most four digits. Internally, the microwave interprets those digits as a four digit string in the form: $$MMSS$$ The first two digits represent minutes and the last two...
leetcode Medium math enumeration May 29, 2026
Practice › LeetCode › LeetCode 33xx ›

LeetCode 3371 - Identify the Largest Outlier in an Array

LeetCode Problem 3371 Difficulty: 🟡 Medium Topics: Array, Hash Table, Counting, Enumeration Solution Problem Understanding The problem gives us an integer array nums containing exactly three types of elements: n - 2 special numbers One element equal to the sum of all special numbers One outlier The task is to return the largest possible value that could serve as the outlier. The important detail is that these roles are determined...
leetcode Medium array hash-table counting enumeration May 29, 2026
Practice › LeetCode › LeetCode 22xx ›

LeetCode 2242 - Maximum Score of a Node Sequence

LeetCode Problem 2242 Difficulty: 🔴 Hard Topics: Array, Graph Theory, Sorting, Enumeration Solution Problem Understanding The problem gives us an undirected graph with n nodes. Each node has a score, and the graph edges define which nodes are directly connected. We must find a valid sequence of exactly four distinct nodes such that every adjacent pair in the sequence has an edge between them. A valid sequence looks like this:...
leetcode Hard array graph-theory sorting enumeration May 29, 2026
Practice › LeetCode › LeetCode 33xx ›

LeetCode 3380 - Maximum Area Rectangle With Point Constraints I

LeetCode Problem 3380 Difficulty: 🟡 Medium Topics: Array, Math, Binary Indexed Tree, Segment Tree, Geometry, Sorting, Enumeration Solution LeetCode 3380 - Maximum Area Rectangle With Point Constraints I Problem Understanding The problem gives us a set of unique points on a 2D plane. We need to determine the largest possible axis-aligned rectangle that can be formed using exactly four of those points as its corners. An axis-aligned rectangle means: The...
leetcode Medium array math binary-indexed-tree segment-tree geometry sorting enumeration May 29, 2026
Practice › LeetCode › LeetCode 19xx ›

LeetCode 1952 - Three Divisors

LeetCode Problem 1952 Difficulty: 🟢 Easy Topics: Math, Enumeration, Number Theory Solution Problem Understanding The problem asks us to determine whether a given integer n has exactly three positive divisors . In other words, we want to check if there are precisely three distinct integers d such that n % d == 0 and d > 0 . For example, the number 4 has divisors 1, 2, and 4, which...
leetcode Easy math enumeration number-theory May 29, 2026
Practice › LeetCode › LeetCode 32xx ›

LeetCode 3257 - Maximum Value Sum by Placing Three Rooks II

LeetCode Problem 3257 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Matrix, Enumeration Solution Problem Understanding We are given an m x n matrix called board , where each cell contains an integer value. We must place exactly three rooks on the board. A rook attacks every cell in the same row and the same column. Therefore, for three rooks to be valid, no two rooks can share either a row...
leetcode Hard array dynamic-programming matrix enumeration May 29, 2026
Practice › LeetCode › LeetCode 29xx ›

LeetCode 2928 - Distribute Candies Among Children I

LeetCode Problem 2928 Difficulty: 🟢 Easy Topics: Math, Combinatorics, Enumeration Solution Problem Understanding The problem asks us to calculate the number of ways to distribute n candies among exactly three children such that no child receives more than a specified limit of candies. In other words, we are looking for all integer triplets (a, b, c) such that a + b + c = n and each of a ,...
leetcode Easy math combinatorics enumeration May 29, 2026
Practice › LeetCode › LeetCode 23xx ›

LeetCode 2306 - Naming a Company

LeetCode Problem 2306 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Bit Manipulation, Enumeration Solution Problem Understanding The problem gives us a list of unique strings called ideas . We must repeatedly choose two different strings, swap their first characters, and determine whether the newly formed strings are both absent from the original list. If both newly generated names do not already exist in ideas , then the ordered pair...
leetcode Hard array hash-table string bit-manipulation enumeration May 29, 2026
Practice › LeetCode › LeetCode 33xx ›

LeetCode 3345 - Smallest Divisible Digit Product I

LeetCode Problem 3345 Difficulty: 🟢 Easy Topics: Math, Enumeration Solution Problem Understanding The problem gives us two integers, n and t . We must find the smallest integer greater than or equal to n whose digit product is divisible by t . The digit product of a number is obtained by multiplying all of its digits together. For example: The digit product of 16 is 1 × 6 = 6...
leetcode Easy math enumeration May 29, 2026
Practice › LeetCode › LeetCode 23xx ›

LeetCode 2309 - Greatest English Letter in Upper and Lower Case

LeetCode Problem 2309 Difficulty: 🟢 Easy Topics: Hash Table, String, Enumeration Solution Problem Understanding The problem gives us a string s containing only uppercase and lowercase English letters. Our task is to find the greatest English letter that appears in both lowercase and uppercase forms somewhere in the string. The answer must be returned as an uppercase letter. To understand this clearly, consider what "greatest" means in this context. Letters...
leetcode Easy hash-table string enumeration May 29, 2026
Practice › LeetCode › LeetCode 20xx ›

LeetCode 2044 - Count Number of Maximum Bitwise-OR Subsets

LeetCode Problem 2044 Difficulty: 🟡 Medium Topics: Array, Backtracking, Bit Manipulation, Enumeration Solution Problem Understanding The problem asks us to examine every possible non-empty subset of the given array nums and compute the bitwise OR value of each subset. Among all these OR values, we need to determine the maximum possible value, then count how many different subsets produce that maximum. A subset is formed by selecting any combination of...
leetcode Medium array backtracking bit-manipulation enumeration May 29, 2026
Practice › LeetCode › LeetCode 17xx ›

LeetCode 1761 - Minimum Degree of a Connected Trio in a Graph

LeetCode Problem 1761 Difficulty: 🔴 Hard Topics: Graph Theory, Enumeration Solution LeetCode 1761 - Minimum Degree of a Connected Trio in a Graph Problem Understanding This problem gives us an undirected graph with n nodes and a list of edges. A connected trio is a group of exactly three distinct nodes where every pair of nodes has an edge between them. In graph theory terms, this is simply a triangle....
leetcode Hard graph-theory enumeration May 29, 2026
Practice › LeetCode › LeetCode 26xx ›

LeetCode 2605 - Form Smallest Number From Two Digit Arrays

LeetCode Problem 2605 Difficulty: 🟢 Easy Topics: Array, Hash Table, Enumeration Solution Problem Understanding The problem gives us two arrays, nums1 and nums2 , where each array contains unique digits from 1 to 9 . We need to construct the smallest possible number such that the number contains at least one digit from each array. The phrase "contains at least one digit from each array" is the key requirement. A...
leetcode Easy array hash-table enumeration May 29, 2026
Practice › LeetCode › LeetCode 18xx ›

LeetCode 1849 - Splitting a String Into Descending Consecutive Values

LeetCode Problem 1849 Difficulty: 🟡 Medium Topics: String, Backtracking, Enumeration Solution Problem Understanding The problem gives us a numeric string s and asks whether it can be split into at least two non-empty substrings such that their integer values form a strictly descending sequence where every adjacent pair differs by exactly 1 . The important detail is that we compare the numerical values of the substrings, not the literal substring...
leetcode Medium string backtracking enumeration May 29, 2026
Practice › LeetCode › LeetCode 28xx ›

LeetCode 2843 - Count Symmetric Integers

LeetCode Problem 2843 Difficulty: 🟢 Easy Topics: Math, Enumeration Solution Problem Understanding The problem asks us to count symmetric integers within a given range [low, high] . A symmetric integer is defined as an integer with an even number of digits , where the sum of the first half of the digits is equal to the sum of the second half. For example, 1221 is symmetric because the sum of...
leetcode Easy math enumeration May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3044 - Most Frequent Prime

LeetCode Problem 3044 Difficulty: 🟡 Medium Topics: Array, Hash Table, Math, Matrix, Counting, Enumeration, Number Theory Solution Problem Understanding The problem asks us to traverse a m x n integer matrix and generate numbers by moving in straight lines along eight possible directions: east, south-east, south, south-west, west, north-west, north, and north-east. Starting from any cell, we can append the digits along a chosen path to form numbers. Importantly, numbers...
leetcode Medium array hash-table math matrix counting enumeration number-theory May 29, 2026
Practice › LeetCode › LeetCode 27xx ›

LeetCode 2735 - Collecting Chocolates

LeetCode Problem 2735 Difficulty: 🟡 Medium Topics: Array, Enumeration Solution LeetCode 2735 - Collecting Chocolates Problem Understanding The problem gives us an array nums , where nums[i] represents the cost of buying a chocolate currently located at index i . Initially, the chocolate at index i is also considered to be of type i . Since there are n positions, there are exactly n chocolate types. The goal is to...
leetcode Medium array enumeration May 29, 2026
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LeetCode 2397 - Maximum Rows Covered by Columns

LeetCode Problem 2397 Difficulty: 🟡 Medium Topics: Array, Backtracking, Bit Manipulation, Matrix, Enumeration Solution Problem Understanding This problem asks us to maximize the number of rows covered in a binary matrix after selecting exactly numSelect columns. Each row is covered if all 1 s in that row are located in the selected columns, or if the row contains only 0 s. The input is an m x n binary matrix,...
leetcode Medium array backtracking bit-manipulation matrix enumeration May 29, 2026
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LeetCode 2951 - Find the Peaks

LeetCode Problem 2951 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding The problem is asking us to identify all the peaks in a given array mountain . A peak is an element that is strictly greater than its immediate neighbors. Importantly, the first and last elements of the array cannot be peaks because they do not have two neighbors. The input is a zero-indexed array of integers mountain with...
leetcode Easy array enumeration May 29, 2026
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LeetCode 2947 - Count Beautiful Substrings I

LeetCode Problem 2947 Difficulty: 🟡 Medium Topics: Hash Table, Math, String, Enumeration, Number Theory, Prefix Sum Solution LeetCode 2947 - Count Beautiful Substrings I Problem Understanding We are given a lowercase English string s and a positive integer k . We must count how many non-empty substrings satisfy the definition of a beautiful substring. For a substring, let: vowels be the number of vowel characters ( a , e ,...
leetcode Medium hash-table math string enumeration number-theory prefix-sum May 29, 2026
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LeetCode 2763 - Sum of Imbalance Numbers of All Subarrays

LeetCode Problem 2763 Difficulty: 🔴 Hard Topics: Array, Hash Table, Enumeration Solution LeetCode 2763 - Sum of Imbalance Numbers of All Subarrays Problem Understanding For any array, its imbalance number is determined after sorting the elements. Suppose we have a subarray and sort it into sarr . We examine every adjacent pair in the sorted order. Whenever the difference between consecutive values is greater than 1 , that pair contributes...
leetcode Hard array hash-table enumeration May 29, 2026
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LeetCode 1999 - Smallest Greater Multiple Made of Two Digits

LeetCode Problem 1999 Difficulty: 🟡 Medium Topics: Math, Enumeration Solution Problem Understanding The problem asks us to find the smallest integer that satisfies three specific conditions. Given an integer k and two digits digit1 and digit2 , we need an integer that is strictly larger than k , is a multiple of k , and consists only of the two given digits . The integer must also fit within the...
leetcode Medium math enumeration May 29, 2026
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LeetCode 2800 - Shortest String That Contains Three Strings

LeetCode Problem 2800 Difficulty: 🟡 Medium Topics: String, Greedy, Enumeration Solution Problem Understanding The problem asks us to construct a string that contains three given strings a , b , and c as substrings while minimizing its length. If multiple strings satisfy the minimum length condition, the lexicographically smallest one must be returned. In other words, the solution must be the shortest possible string that embeds all three input strings,...
leetcode Medium string greedy enumeration May 29, 2026
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LeetCode 3200 - Maximum Height of a Triangle

LeetCode Problem 3200 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 3200 - Maximum Height of a Triangle Problem Understanding The problem gives us two integers, red and blue , representing the number of red and blue balls available. We want to build a triangle where: Row 1 contains exactly 1 ball Row 2 contains exactly 2 balls Row 3 contains exactly 3 balls And so on There are two...
leetcode Easy array enumeration May 29, 2026
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LeetCode 3398 - Smallest Substring With Identical Characters I

LeetCode Problem 3398 Difficulty: 🔴 Hard Topics: Array, Binary Search, Enumeration Solution Problem Understanding The problem gives us a binary string s consisting of only '0' and '1' characters and an integer numOps representing the maximum number of bit flips we can perform. The objective is to minimize the length of the longest contiguous substring where all characters are identical after performing at most numOps flips. In simpler terms, we...
leetcode Hard array binary-search enumeration May 29, 2026
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LeetCode 2259 - Remove Digit From Number to Maximize Result

LeetCode Problem 2259 Difficulty: 🟢 Easy Topics: String, Greedy, Enumeration Solution LeetCode 2259 - Remove Digit From Number to Maximize Result Problem Understanding The problem gives us a string called number , which represents a positive integer, and a character digit , which is guaranteed to appear at least once inside number . Our task is to remove exactly one occurrence of digit from the string so that the resulting...
leetcode Easy string greedy enumeration May 29, 2026
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LeetCode 1863 - Sum of All Subset XOR Totals

LeetCode Problem 1863 Difficulty: 🟢 Easy Topics: Array, Math, Backtracking, Bit Manipulation, Combinatorics, Enumeration Solution LeetCode 1863 - Sum of All Subset XOR Totals Problem Understanding This problem asks us to compute the sum of the XOR values of every possible subset of a given array. A subset is formed by choosing any combination of elements from the array, including the empty subset and the full array itself. Since an...
leetcode Easy array math backtracking bit-manipulation combinatorics enumeration May 29, 2026
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LeetCode 2860 - Happy Students

LeetCode Problem 2860 Difficulty: 🟡 Medium Topics: Array, Sorting, Enumeration Solution Problem Understanding The problem asks us to determine the number of ways to select a subset of students from a class such that every student is happy according to the given rules. Each student has a number nums[i] that represents a threshold. A student is happy if they are selected and the total number of selected students is strictly...
leetcode Medium array sorting enumeration May 29, 2026
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LeetCode 1862 - Sum of Floored Pairs

LeetCode Problem 1862 Difficulty: 🔴 Hard Topics: Array, Math, Binary Search, Counting, Enumeration, Prefix Sum Solution Problem Understanding The problem asks us to calculate the sum of the integer division results, floor(nums[i] / nums[j]) , for every pair of elements (i, j) in a given array nums . Here, floor() represents the largest integer less than or equal to the division result. The array nums can have up to 10^5...
leetcode Hard array math binary-search counting enumeration prefix-sum May 29, 2026
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LeetCode 3234 - Count the Number of Substrings With Dominant Ones

LeetCode Problem 3234 Difficulty: 🟡 Medium Topics: String, Enumeration Solution Problem Understanding We are given a binary string s , containing only '0' and '1' . We must count how many substrings satisfy a special condition called "dominant ones". For any substring: Let zeros be the number of '0' characters Let ones be the number of '1' characters The substring is considered valid if: $$\text{ones} \geq (\text{zeros})^2$$ The task is...
leetcode Medium string enumeration May 29, 2026
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LeetCode 2014 - Longest Subsequence Repeated k Times

LeetCode Problem 2014 Difficulty: 🔴 Hard Topics: Hash Table, Two Pointers, String, Backtracking, Counting, Enumeration Solution Problem Understanding The problem asks us to find the longest subsequence of a string s that can be repeated k times while still being a subsequence of s . A subsequence is derived by deleting zero or more characters from a string without changing the order of the remaining characters. A subsequence seq repeated...
leetcode Hard hash-table two-pointers string backtracking counting enumeration May 29, 2026
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LeetCode 2975 - Maximum Square Area by Removing Fences From a Field

LeetCode Problem 2975 Difficulty: 🟡 Medium Topics: Array, Hash Table, Enumeration Solution Problem Understanding The field is represented as a large rectangle whose outer boundaries are fixed fences. Inside the field, additional horizontal and vertical fences divide the area into smaller sections. A horizontal fence spans the entire width of the field at a specific row coordinate, and a vertical fence spans the entire height of the field at a...
leetcode Medium array hash-table enumeration May 29, 2026
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LeetCode 2367 - Number of Arithmetic Triplets

LeetCode Problem 2367 Difficulty: 🟢 Easy Topics: Array, Hash Table, Two Pointers, Enumeration Solution Problem Understanding The problem requires us to find the number of arithmetic triplets in a strictly increasing array of integers. An arithmetic triplet (i, j, k) satisfies the conditions i < j < k , nums[j] - nums[i] == diff , and nums[k] - nums[j] == diff . Essentially, we are looking for sequences of three...
leetcode Easy array hash-table two-pointers enumeration May 29, 2026
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LeetCode 2151 - Maximum Good People Based on Statements

LeetCode Problem 2151 Difficulty: 🔴 Hard Topics: Array, Backtracking, Bit Manipulation, Enumeration Solution Problem Understanding The problem asks us to determine the maximum number of good people in a group given a set of statements about each other. Each person can either be good (always tells the truth) or bad (may lie or tell the truth). The input is a square 2D array statements of size n x n ,...
leetcode Hard array backtracking bit-manipulation enumeration May 29, 2026
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LeetCode 3127 - Make a Square with the Same Color

LeetCode Problem 3127 Difficulty: 🟢 Easy Topics: Array, Matrix, Enumeration Solution Problem Understanding This problem gives us a fixed 3 x 3 grid containing only two possible characters, 'B' for black and 'W' for white. We are allowed to change the color of at most one cell. The goal is to determine whether, after performing zero or one modification, the grid can contain at least one 2 x 2 subgrid...
leetcode Easy array matrix enumeration May 29, 2026
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LeetCode 2417 - Closest Fair Integer

LeetCode Problem 2417 Difficulty: 🟡 Medium Topics: Math, Enumeration Solution Problem Understanding In this problem, we are given a positive integer n , and we must find the smallest integer greater than or equal to n that is considered "fair". A number is fair when the count of even digits is exactly equal to the count of odd digits. For example: 10 is fair because it contains one even digit...
leetcode Medium math enumeration May 29, 2026
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LeetCode 2081 - Sum of k-Mirror Numbers

LeetCode Problem 2081 Difficulty: 🔴 Hard Topics: Math, Enumeration Solution Problem Understanding The problem asks us to find the sum of the n smallest k-mirror numbers , where a k-mirror number is a positive integer that reads the same forwards and backwards both in base-10 and in base- k . The inputs are k , representing the base for the mirror property, and n , the count of the smallest...
leetcode Hard math enumeration May 29, 2026
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LeetCode 2212 - Maximum Points in an Archery Competition

LeetCode Problem 2212 Difficulty: 🟡 Medium Topics: Array, Backtracking, Bit Manipulation, Enumeration Solution Problem Understanding The problem is asking us to determine the optimal way for Bob to distribute his numArrows across 12 scoring sections (from 0 to 11) in an archery competition in order to maximize his total points against Alice. Alice's arrow distribution is given in aliceArrows . The scoring rules are such that for each section, the...
leetcode Medium array backtracking bit-manipulation enumeration May 29, 2026
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LeetCode 2765 - Longest Alternating Subarray

LeetCode Problem 2765 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution LeetCode 2765 - Longest Alternating Subarray Problem Understanding This problem asks us to find the longest contiguous subarray that follows a very specific alternating pattern. Given an integer array nums , we need to identify subarrays where: The subarray length is at least 2 . The second element is exactly one greater than the first element. Every subsequent difference alternates...
leetcode Easy array enumeration May 29, 2026
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LeetCode 2844 - Minimum Operations to Make a Special Number

LeetCode Problem 2844 Difficulty: 🟡 Medium Topics: Math, String, Greedy, Enumeration Solution Problem Understanding The problem asks us to transform a string num representing a non-negative integer into a special number by deleting as few digits as possible. A special number is defined as an integer divisible by 25. In decimal notation, a number is divisible by 25 if its last two digits are one of 00 , 25 ,...
leetcode Medium math string greedy enumeration May 29, 2026
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LeetCode 1995 - Count Special Quadruplets

LeetCode Problem 1995 Difficulty: 🟢 Easy Topics: Array, Hash Table, Enumeration Solution Problem Understanding The problem asks us to count the number of distinct quadruplets (a, b, c, d) in a given array nums such that the sum of the first three elements equals the fourth, i.e., nums[a] + nums[b] + nums[c] == nums[d] , and the indices satisfy a < b < c < d . In simpler terms,...
leetcode Easy array hash-table enumeration May 29, 2026
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LeetCode 2749 - Minimum Operations to Make the Integer Zero

LeetCode Problem 2749 Difficulty: 🟡 Medium Topics: Bit Manipulation, Brainteaser, Enumeration Solution Problem Understanding The problem gives us two integers, num1 and num2 . In one operation, we may choose any integer i between 0 and 60 , inclusive, and subtract the value 2^i + num2 from num1 . The goal is to determine the minimum number of operations required to make num1 become exactly 0 . If it is...
leetcode Medium bit-manipulation brainteaser enumeration May 29, 2026
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LeetCode 2468 - Split Message Based on Limit

LeetCode Problem 2468 Difficulty: 🔴 Hard Topics: String, Enumeration Solution LeetCode 2468 - Split Message Based on Limit Problem Understanding This problem asks us to divide a message into multiple parts while respecting a strict maximum length constraint for every part. Each part must include a suffix in the format "<a/b>" , where: a is the current part number, starting from 1 b is the total number of parts The...
leetcode Hard string enumeration May 29, 2026
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LeetCode 1956 - Minimum Time For K Virus Variants to Spread

LeetCode Problem 1956 Difficulty: 🔴 Hard Topics: Array, Math, Binary Search, Geometry, Enumeration Solution Problem Understanding The problem describes multiple virus variants spreading across an infinite 2D grid. Each virus starts from its own origin point on day 0 . Every day, a virus spreads one step in the four cardinal directions, which means after d days, a virus can reach every point whose Manhattan distance from its origin is...
leetcode Hard array math binary-search geometry enumeration May 29, 2026
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LeetCode 2440 - Create Components With Same Value

LeetCode Problem 2440 Difficulty: 🔴 Hard Topics: Array, Math, Tree, Depth-First Search, Enumeration Solution Problem Understanding This problem is asking us to take an undirected tree where each node has a numerical value and determine how many edges we can remove such that every resulting connected component has the same total value. The tree is represented by a list of node values nums and a list of edges edges that...
leetcode Hard array math tree depth-first-search enumeration May 29, 2026
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LeetCode 2778 - Sum of Squares of Special Elements

LeetCode Problem 2778 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding This problem asks us to compute the sum of squares of certain elements in an array, specifically the special elements . The array nums is 1-indexed , meaning the first element is at index 1 (not 0). An element nums[i] is considered special if its 1-based index divides the length of the array n exactly. In other words,...
leetcode Easy array enumeration May 29, 2026
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LeetCode 2437 - Number of Valid Clock Times

LeetCode Problem 2437 Difficulty: 🟢 Easy Topics: String, Enumeration Solution Problem Understanding The problem asks us to determine the number of valid times that can be formed from a partially known digital clock string of the format "hh:mm" , where unknown digits are represented by '?' . Each '?' can be replaced with any digit from 0 to 9 , but the resulting hour ( hh ) must be in...
leetcode Easy string enumeration May 29, 2026
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LeetCode 2261 - K Divisible Elements Subarrays

LeetCode Problem 2261 Difficulty: 🟡 Medium Topics: Array, Hash Table, Trie, Rolling Hash, Hash Function, Enumeration Solution Problem Understanding This problem requires counting the number of distinct subarrays of a given integer array nums that satisfy a specific constraint: each subarray can contain at most k elements divisible by p . A subarray is a contiguous slice of the array, and "distinct" means either differing in length or differing in...
leetcode Medium array hash-table trie rolling-hash hash-function enumeration May 29, 2026
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LeetCode 3309 - Maximum Possible Number by Binary Concatenation

LeetCode Problem 3309 Difficulty: 🟡 Medium Topics: Array, Bit Manipulation, Enumeration Solution Problem Understanding The problem is asking for the maximum integer value that can be created by concatenating the binary representations of all elements in a list of three integers. Each number should be converted to its binary representation without leading zeros. After conversion, the binary strings can be concatenated in any order. The resulting binary string should then...
leetcode Medium array bit-manipulation enumeration May 29, 2026
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LeetCode 1958 - Check if Move is Legal

LeetCode Problem 1958 Difficulty: 🟡 Medium Topics: Array, Matrix, Enumeration Solution Problem Understanding This problem asks us to determine whether a move in a board game is legal based on specific line rules. The board is an 8 x 8 matrix where cells can be empty '.' , white 'W' , or black 'B' . A move is represented by the row and column (rMove, cMove) and the color of...
leetcode Medium array matrix enumeration May 29, 2026
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LeetCode 2198 - Number of Single Divisor Triplets

LeetCode Problem 2198 Difficulty: 🟡 Medium Topics: Array, Counting, Enumeration Solution Problem Understanding The problem asks us to count how many ordered triplets of distinct indices (i, j, k) satisfy a very specific divisibility condition. For every triplet, we compute: $$\text{sum} = nums[i] + nums[j] + nums[k]$$ The triplet is considered valid if this sum is divisible by exactly one of the three participating values: nums[i] nums[j] nums[k] The indices...
leetcode Medium array counting enumeration May 29, 2026
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LeetCode 2234 - Maximum Total Beauty of the Gardens

LeetCode Problem 2234 Difficulty: 🔴 Hard Topics: Array, Two Pointers, Binary Search, Greedy, Sorting, Enumeration, Prefix Sum Solution Problem Understanding In this problem, we are given several gardens, where flowers[i] represents how many flowers are already planted in the i-th garden. We are also given a limited number of additional flowers, newFlowers , that we may distribute among the gardens. The goal is to maximize the total beauty score after...
leetcode Hard array two-pointers binary-search greedy sorting enumeration prefix-sum May 29, 2026
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LeetCode 2122 - Recover the Original Array

LeetCode Problem 2122 Difficulty: 🔴 Hard Topics: Array, Hash Table, Two Pointers, Sorting, Enumeration Solution Problem Understanding The problem presents a scenario in which Alice has an original array arr of length n consisting of positive integers. She chooses a positive integer k and generates two new arrays: lower and higher . The array lower is formed by subtracting k from each element of arr , while higher is formed...
leetcode Hard array hash-table two-pointers sorting enumeration May 29, 2026
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LeetCode 3010 - Divide an Array Into Subarrays With Minimum Cost I

LeetCode Problem 3010 Difficulty: 🟢 Easy Topics: Array, Sorting, Enumeration Solution Problem Understanding The problem asks us to split a given array nums into exactly three disjoint contiguous subarrays and minimize the sum of their costs . The important detail is how cost is defined. The cost of a subarray is simply its first element . For example: [1,2,3] has cost 1 [10,5] has cost 10 Since we must divide...
leetcode Easy array sorting enumeration May 29, 2026
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LeetCode 3272 - Find the Count of Good Integers

LeetCode Problem 3272 Difficulty: 🔴 Hard Topics: Hash Table, Math, Combinatorics, Enumeration Solution Problem Understanding The problem asks us to count n-digit integers that are "good" with respect to a given integer k . A "good" integer is one whose digits can be rearranged to form a k-palindromic integer . A k-palindromic integer is defined as an integer that satisfies two properties: it is a palindrome (reads the same forwards...
leetcode Hard hash-table math combinatorics enumeration May 29, 2026
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LeetCode 2552 - Count Increasing Quadruplets

LeetCode Problem 2552 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Binary Indexed Tree, Enumeration, Prefix Sum Solution Problem Understanding The problem asks us to count the number of increasing quadruplets (i, j, k, l) in a 0-indexed array nums of size n , where nums is a permutation of the integers from 1 to n . A quadruplet is considered increasing if it satisfies both the index order 0 <=...
leetcode Hard array dynamic-programming binary-indexed-tree enumeration prefix-sum May 29, 2026
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LeetCode 3265 - Count Almost Equal Pairs I

LeetCode Problem 3265 Difficulty: 🟡 Medium Topics: Array, Hash Table, Sorting, Counting, Enumeration Solution Problem Understanding The problem asks us to find the number of index pairs (i, j) in an array nums such that i < j and the integers nums[i] and nums[j] are almost equal . Two integers are considered almost equal if you can make them equal by swapping any two digits at most once in either...
leetcode Medium array hash-table sorting counting enumeration May 29, 2026
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LeetCode 2048 - Next Greater Numerically Balanced Number

LeetCode Problem 2048 Difficulty: 🟡 Medium Topics: Hash Table, Math, Backtracking, Counting, Enumeration Solution Problem Understanding The problem asks us to find the smallest integer strictly greater than n such that the number is numerically balanced. A number is numerically balanced when every digit that appears in the number appears exactly as many times as its value. For example: 22 is balanced because digit 2 appears exactly 2 times. 1333...
leetcode Medium hash-table math backtracking counting enumeration May 29, 2026
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LeetCode 2970 - Count the Number of Incremovable Subarrays I

LeetCode Problem 2970 Difficulty: 🟢 Easy Topics: Array, Two Pointers, Binary Search, Enumeration Solution Problem Understanding The problem asks us to count all subarrays of a given array nums such that if we remove the subarray , the remaining array becomes strictly increasing. A strictly increasing array is one where each element is less than the next element. For example, [1,2,3] is strictly increasing, while [1,2,2] or [3,2,1] are not....
leetcode Easy array two-pointers binary-search enumeration May 29, 2026
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LeetCode 2929 - Distribute Candies Among Children II

LeetCode Problem 2929 Difficulty: 🟡 Medium Topics: Math, Combinatorics, Enumeration Solution Problem Understanding The problem asks us to calculate the total number of ways to distribute n candies among exactly three children, with the constraint that no child can receive more than limit candies. Essentially, we are asked to enumerate all possible triplets (a, b, c) of non-negative integers that satisfy two conditions: a + b + c = n...
leetcode Medium math combinatorics enumeration May 29, 2026
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LeetCode 3114 - Latest Time You Can Obtain After Replacing Characters

LeetCode Problem 3114 Difficulty: 🟢 Easy Topics: String, Enumeration Solution Problem Understanding The problem gives us a string representing a time in 12-hour format using the pattern "HH:MM" . Some characters may already be fixed digits, while others are replaced with "?" . Our task is to replace every "?" with a digit so that the resulting time is both valid and as large as possible chronologically. The valid hour...
leetcode Easy string enumeration May 29, 2026
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LeetCode 2272 - Substring With Largest Variance

LeetCode Problem 2272 Difficulty: 🔴 Hard Topics: Hash Table, String, Dynamic Programming, Enumeration Solution Problem Understanding This problem asks us to find the maximum possible variance among all substrings of a given string. The string contains only lowercase English letters, and the variance of a substring is defined as the largest difference between the counts of any two characters that both appear in that substring. The important detail is that...
leetcode Hard hash-table string dynamic-programming enumeration May 29, 2026
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LeetCode 3132 - Find the Integer Added to Array II

LeetCode Problem 3132 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Sorting, Enumeration Solution Problem Understanding We are given two integer arrays, nums1 and nums2 . The array nums2 was created from nums1 using two operations: Remove exactly two elements from nums1 . Add the same integer x to every remaining element. After these operations, the resulting multiset of values becomes exactly equal to nums2 . The order of elements does...
leetcode Medium array two-pointers sorting enumeration May 29, 2026
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LeetCode 2443 - Sum of Number and Its Reverse

LeetCode Problem 2443 Difficulty: 🟡 Medium Topics: Math, Enumeration Solution Here’s a complete, detailed solution guide for LeetCode 2443 - Sum of Number and Its Reverse , fully following your formatting rules. Problem Understanding The problem asks whether a given non-negative integer num can be expressed as the sum of a non-negative integer x and its reversed version reverse(x) . In other words, we are asked to find whether there...
leetcode Medium math enumeration May 29, 2026
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LeetCode 2959 - Number of Possible Sets of Closing Branches

LeetCode Problem 2959 Difficulty: 🔴 Hard Topics: Bit Manipulation, Graph Theory, Heap (Priority Queue), Enumeration, Shortest Path Solution Problem Understanding This problem asks us to determine the number of possible sets of branches that can be closed such that the maximum distance between any pair of remaining open branches does not exceed a given maxDistance . The input consists of n branches connected by undirected roads with given weights, where...
leetcode Hard bit-manipulation graph-theory heap-(priority-queue) enumeration shortest-path May 29, 2026
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LeetCode 3027 - Find the Number of Ways to Place People II

LeetCode Problem 3027 Difficulty: 🔴 Hard Topics: Array, Math, Geometry, Sorting, Enumeration Solution Problem Understanding The problem asks us to determine how many valid placements of Alice and Bob exist on a 2D grid of points such that Alice can build a rectangular fence with her position as the upper left corner and Bob’s position as the lower right corner . A placement is only valid if no other person...
leetcode Hard array math geometry sorting enumeration May 29, 2026
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LeetCode 2761 - Prime Pairs With Target Sum

LeetCode Problem 2761 Difficulty: 🟡 Medium Topics: Array, Math, Enumeration, Number Theory Solution Problem Understanding The problem asks us to find all pairs of prime numbers (x, y) such that both numbers are between 1 and n inclusive, their sum equals n , and x <= y . The input is a single integer n , and the output is a sorted list of pairs [x, y] meeting these conditions,...
leetcode Medium array math enumeration number-theory May 29, 2026
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LeetCode 2240 - Number of Ways to Buy Pens and Pencils

LeetCode Problem 2240 Difficulty: 🟡 Medium Topics: Math, Enumeration Solution Problem Understanding The problem asks us to determine the number of distinct ways to spend a given amount of money, total , on pens and pencils, each with fixed costs, cost1 for pens and cost2 for pencils. You can buy any non-negative number of each item, including zero, as long as the total cost does not exceed your budget. The...
leetcode Medium math enumeration May 29, 2026
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LeetCode 2171 - Removing Minimum Number of Magic Beans

LeetCode Problem 2171 Difficulty: 🟡 Medium Topics: Array, Greedy, Sorting, Enumeration, Prefix Sum Solution Problem Understanding The problem asks us to remove beans from bags in such a way that all non-empty bags have the same number of beans while minimizing the total number of beans removed. Each element in the input array beans represents a bag with a positive number of beans. We are allowed to remove any number...
leetcode Medium array greedy sorting enumeration prefix-sum May 29, 2026
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LeetCode 2249 - Count Lattice Points Inside a Circle

LeetCode Problem 2249 Difficulty: 🟡 Medium Topics: Array, Hash Table, Math, Geometry, Enumeration Solution Problem Understanding The problem asks us to determine how many lattice points lie inside at least one of a set of circles on a 2D grid. Each circle is represented by a triplet [xi, yi, ri] , where (xi, yi) is the circle's center and ri is its radius. A lattice point is any point on...
leetcode Medium array hash-table math geometry enumeration May 29, 2026
Practice › LeetCode › LeetCode 19xx ›

LeetCode 1925 - Count Square Sum Triples

LeetCode Problem 1925 Difficulty: 🟢 Easy Topics: Math, Enumeration Solution Problem Understanding This problem asks us to count all ordered triples (a, b, c) such that: 1 <= a, b, c <= n a² + b² = c² This is the classic Pythagorean theorem relationship. Any triple satisfying this condition is called a square triple in the problem statement. The important detail is that the triples are ordered. This means...
leetcode Easy math enumeration May 29, 2026
Practice › LeetCode › LeetCode 22xx ›

LeetCode 2232 - Minimize Result by Adding Parentheses to Expression

LeetCode Problem 2232 Difficulty: 🟡 Medium Topics: String, Enumeration Solution Problem Understanding The problem presents a string expression in the form "<num1>+<num2>" , where both <num1> and <num2> are positive integers represented as strings. The task is to insert exactly one pair of parentheses such that the left parenthesis appears to the left of the plus sign and the right parenthesis appears to the right of the plus sign ,...
leetcode Medium string enumeration May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3020 - Find the Maximum Number of Elements in Subset

LeetCode Problem 3020 Difficulty: 🟡 Medium Topics: Array, Hash Table, Enumeration Solution Problem Understanding The problem gives us an array of positive integers and asks us to choose the largest possible subset that can be rearranged into a very specific symmetric structure. The required structure looks like this: $$[x, x^2, x^4, \dots, x^{k/2}, x^k, x^{k/2}, \dots, x^4, x^2, x]$$ where $k$ is a power of two. The sequence grows by...
leetcode Medium array hash-table enumeration May 29, 2026
Practice › LeetCode › LeetCode 31xx ›

LeetCode 3139 - Minimum Cost to Equalize Array

LeetCode Problem 3139 Difficulty: 🔴 Hard Topics: Array, Greedy, Enumeration Solution Problem Understanding This problem asks us to determine the minimum cost to make all elements in an array equal. You are allowed two types of operations: increment a single element at a cost of cost1 , or increment any two distinct elements simultaneously at a cost of cost2 . The goal is to compute the cheapest sequence of these...
leetcode Hard array greedy enumeration May 29, 2026
Practice › LeetCode › LeetCode 33xx ›

LeetCode 3389 - Minimum Operations to Make Character Frequencies Equal

LeetCode Problem 3389 Difficulty: 🔴 Hard Topics: Hash Table, String, Dynamic Programming, Counting, Enumeration Solution Problem Understanding The problem requires transforming a given string s into a good string , where a good string is defined as one in which every character appears the same number of times. The operations allowed include deleting a character, inserting a character, or incrementing a character to the next letter in the alphabet (with...
leetcode Hard hash-table string dynamic-programming counting enumeration May 29, 2026
Practice › LeetCode › LeetCode 24xx ›

LeetCode 2427 - Number of Common Factors

LeetCode Problem 2427 Difficulty: 🟢 Easy Topics: Math, Enumeration, Number Theory Solution Problem Understanding The problem gives us two positive integers, a and b , and asks us to count how many integers divide both numbers evenly. A number x is considered a common factor if: a % x == 0 b % x == 0 This means x divides both integers without leaving a remainder. For example, if a...
leetcode Easy math enumeration number-theory May 29, 2026
Practice › LeetCode › LeetCode 29xx ›

LeetCode 2934 - Minimum Operations to Maximize Last Elements in Arrays

LeetCode Problem 2934 Difficulty: 🟡 Medium Topics: Array, Enumeration Solution LeetCode 2934 - Minimum Operations to Maximize Last Elements in Arrays Problem Understanding You are given two arrays, nums1 and nums2 , both of the same length n . For every index i , you may optionally swap the pair (nums1[i], nums2[i]) . Each swap counts as one operation. Your goal is to make the last element of each array...
leetcode Medium array enumeration May 29, 2026
Practice › LeetCode › LeetCode 31xx ›

LeetCode 3197 - Find the Minimum Area to Cover All Ones II

LeetCode Problem 3197 Difficulty: 🔴 Hard Topics: Array, Matrix, Enumeration Solution Problem Understanding The problem gives us a binary matrix grid , where each cell contains either 0 or 1 . Our goal is to place exactly three non-overlapping axis-aligned rectangles so that every cell containing 1 is covered by at least one rectangle. Each rectangle must satisfy several conditions: Its sides must be parallel to the grid axes. It...
leetcode Hard array matrix enumeration May 29, 2026
Practice › LeetCode › LeetCode 27xx ›

LeetCode 2708 - Maximum Strength of a Group

LeetCode Problem 2708 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Greedy, Bit Manipulation, Sorting, Enumeration Solution Problem Understanding The problem asks us to select a non-empty subset of integers from a given array nums such that the product of the numbers in the subset is maximized. Each number represents a student’s exam score, and the subset represents a group of students. The "strength" of a group is the product...
leetcode Medium array dynamic-programming backtracking greedy bit-manipulation sorting enumeration May 29, 2026
Practice › LeetCode › LeetCode 32xx ›

LeetCode 3256 - Maximum Value Sum by Placing Three Rooks I

LeetCode Problem 3256 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Matrix, Enumeration Solution Problem Understanding We are given an m x n matrix called board , where each cell contains an integer value. We must place exactly three rooks on the board. A rook attacks every square in the same row and the same column. Therefore, for three rooks to be valid: No two rooks can share the same row...
leetcode Hard array dynamic-programming matrix enumeration May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3091 - Apply Operations to Make Sum of Array Greater Than or Equal to k

LeetCode Problem 3091 Difficulty: 🟡 Medium Topics: Math, Greedy, Enumeration Solution Problem Understanding The problem gives us a single positive integer k . We start with an array containing exactly one element: nums = [1] We are allowed to perform two kinds of operations any number of times: Increase the value of any existing element by 1 Duplicate any existing element and append the duplicate to the array Our goal...
leetcode Medium math greedy enumeration May 29, 2026
Practice › LeetCode › LeetCode 23xx ›

LeetCode 2310 - Sum of Numbers With Units Digit K

LeetCode Problem 2310 Difficulty: 🟡 Medium Topics: Math, Dynamic Programming, Greedy, Enumeration Solution Problem Understanding This problem asks us to construct a set of positive integers such that: Every number in the set has a units digit equal to k . The sum of all numbers equals num . We want the smallest possible number of integers in the set. If it is impossible to create such a set, we...
leetcode Medium math dynamic-programming greedy enumeration May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3001 - Minimum Moves to Capture The Queen

LeetCode Problem 3001 Difficulty: 🟡 Medium Topics: Math, Enumeration Solution LeetCode 3001 - Minimum Moves to Capture The Queen Problem Understanding This problem gives us the positions of three chess pieces on a standard 8 x 8 chessboard: A white rook at (a, b) A white bishop at (c, d) A black queen at (e, f) We are allowed to move only the white pieces. The queen remains stationary. Our...
leetcode Medium math enumeration May 29, 2026
Practice › LeetCode › LeetCode 16xx ›

LeetCode 1620 - Coordinate With Maximum Network Quality

LeetCode Problem 1620 Difficulty: 🟡 Medium Topics: Array, Enumeration Solution Problem Understanding The problem asks us to find the integral coordinate on a 2D plane where the network quality is maximized. We are given several network towers, each defined by its (x, y) coordinates and quality factor q . A tower contributes to the network quality at a specific coordinate if it is within the given radius . The contribution...
leetcode Medium array enumeration May 28, 2026
Practice › LeetCode › LeetCode 09xx ›

LeetCode 949 - Largest Time for Given Digits

LeetCode Problem 949 Difficulty: 🟡 Medium Topics: Array, String, Backtracking, Enumeration Solution Problem Understanding The problem provides an array of exactly four digits. Using each digit exactly once, we must construct the latest possible valid 24-hour time in the format "HH:MM" . A valid 24-hour time has two important constraints: The hour portion, HH , must be between 00 and 23 The minute portion, MM , must be between 00...
leetcode Medium array string backtracking enumeration May 28, 2026
Practice › LeetCode › LeetCode 08xx ›

LeetCode 800 - Similar RGB Color

LeetCode Problem 800 Difficulty: 🟢 Easy Topics: Math, String, Enumeration Solution Problem Understanding The problem is asking us to find the shorthand RGB color that is most similar to a given full-length RGB color string. An RGB color is represented as a hexadecimal string of the form "#RRGGBB" , where each pair of characters ( RR , GG , BB ) represents the red, green, and blue components, respectively, using...
leetcode Easy math string enumeration May 28, 2026
Practice › LeetCode › LeetCode 20xx ›

LeetCode 2018 - Check if Word Can Be Placed In Crossword

LeetCode Problem 2018 Difficulty: 🟡 Medium Topics: Array, Matrix, Enumeration Solution Problem Understanding This problem asks us to determine whether a given word can be legally placed into a crossword board while respecting crossword placement rules. The input consists of a 2D matrix called board , where each cell can contain one of three possible values: '#' , representing a blocked cell that cannot be used. ' ' , representing...
leetcode Medium array matrix enumeration May 28, 2026
Practice › LeetCode › LeetCode 16xx ›

LeetCode 1625 - Lexicographically Smallest String After Applying Operations

LeetCode Problem 1625 Difficulty: 🟡 Medium Topics: String, Depth-First Search, Breadth-First Search, Enumeration Solution Problem Understanding The problem gives us a numeric string s of even length and two operations that can be performed any number of times in any order. The first operation adds the integer a to every digit located at an odd index. Since digits must remain between 0 and 9 , the addition wraps around using...
leetcode Medium string depth-first-search breadth-first-search enumeration May 28, 2026
Practice › LeetCode › LeetCode 04xx ›

LeetCode 479 - Largest Palindrome Product

LeetCode Problem 479 Difficulty: 🔴 Hard Topics: Math, Enumeration Solution Largest Palindrome Product Problem Understanding The problem asks us to find the largest palindrome number that can be written as the product of two n -digit integers. A palindrome is a number that reads the same forward and backward. For example, 9009 is a palindrome because reversing its digits still gives 9009 . The input is a single integer n...
leetcode Hard math enumeration May 28, 2026
Practice › LeetCode › LeetCode 20xx ›

LeetCode 2025 - Maximum Number of Ways to Partition an Array

LeetCode Problem 2025 Difficulty: 🔴 Hard Topics: Array, Hash Table, Counting, Enumeration, Prefix Sum Solution Problem Understanding The problem asks us to count how many valid partition points exist in an array after optionally changing at most one element to a given value k . A partition is defined by a pivot index pivot such that: 1 <= pivot < n The sum of elements on the left side equals...
leetcode Hard array hash-table counting enumeration prefix-sum May 28, 2026
Practice › LeetCode › LeetCode 12xx ›

LeetCode 1291 - Sequential Digits

LeetCode Problem 1291 Difficulty: 🟡 Medium Topics: Enumeration Solution Problem Understanding The problem asks us to find all integers within a given range [low, high] whose digits are sequential , meaning that each digit is exactly one greater than the previous digit. For instance, 123 is sequential because 2 = 1 + 1 and 3 = 2 + 1 , but 135 is not sequential because the digits do not...
leetcode Medium enumeration May 28, 2026
Practice › LeetCode › LeetCode 09xx ›

LeetCode 906 - Super Palindromes

LeetCode Problem 906 Difficulty: 🔴 Hard Topics: Math, String, Enumeration Solution LeetCode 906 - Super Palindromes Problem Understanding This problem asks us to count how many numbers within a given inclusive range are "super-palindromes". A number is considered a super-palindrome if both of the following conditions are true: The number itself is a palindrome. The number is the square of another palindrome. For example: 121 is a palindrome. 121 =...
leetcode Hard math string enumeration May 28, 2026
Practice › LeetCode › LeetCode 16xx ›

LeetCode 1617 - Count Subtrees With Max Distance Between Cities

LeetCode Problem 1617 Difficulty: 🔴 Hard Topics: Dynamic Programming, Bit Manipulation, Tree, Enumeration, Bitmask Solution Problem Understanding The input describes an undirected tree with n cities. Since the graph is a tree, there are exactly n - 1 edges and there is a unique simple path between every pair of cities. The problem asks us to examine every possible connected subset of cities. A subset is considered a valid subtree...
leetcode Hard dynamic-programming bit-manipulation tree enumeration bitmask May 28, 2026
Practice › LeetCode › LeetCode 15xx ›

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

LeetCode Problem 1566 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding The problem gives us an integer array arr and two integers, m and k . We need to determine whether there exists a contiguous subarray of length m that repeats consecutively at least k times. A pattern is considered valid only if: The repeated segments are consecutive Each repeated segment has exactly length m The repetitions do not...
leetcode Easy array enumeration May 28, 2026
Practice › LeetCode › LeetCode 16xx ›

LeetCode 1638 - Count Substrings That Differ by One Character

LeetCode Problem 1638 Difficulty: 🟡 Medium Topics: Hash Table, String, Dynamic Programming, Enumeration Solution Problem Understanding The problem asks us to count how many pairs of substrings, one taken from s and one taken from t , differ by exactly one character. A substring is contiguous, so for a string like "abcde" , valid substrings include "a" , "bc" , "abcd" , and "cde" . We are not allowed to...
leetcode Medium hash-table string dynamic-programming enumeration May 28, 2026
Practice › LeetCode › LeetCode 06xx ›

LeetCode 681 - Next Closest Time

LeetCode Problem 681 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking, Enumeration Solution Problem Understanding The problem gives us a valid time string in the format "HH:MM" and asks us to construct the next chronological time using only the digits already present in the original time. The important detail is that digits may be reused any number of times. If the input is "19:34" , the allowed digits are {1,...
leetcode Medium hash-table string backtracking enumeration May 28, 2026
Practice › LeetCode › LeetCode 08xx ›

LeetCode 816 - Ambiguous Coordinates

LeetCode Problem 816 Difficulty: 🟡 Medium Topics: String, Backtracking, Enumeration Solution Problem Understanding The problem gives us a compressed string representation of a 2D coordinate. Originally, the coordinate looked something like "(1, 3)" or "(2, 0.5)" , but all commas, spaces, and decimal points were removed. Our task is to reconstruct every possible valid original coordinate pair. For example: "(1, 3)" -> "(13)" "(2, 0.5)" -> "(205)" Given the compressed...
leetcode Medium string backtracking enumeration May 28, 2026
Practice › LeetCode › LeetCode 09xx ›

LeetCode 970 - Powerful Integers

LeetCode Problem 970 Difficulty: 🟡 Medium Topics: Hash Table, Math, Enumeration Solution LeetCode 970 - Powerful Integers Problem Understanding This problem asks us to generate all integers that can be written in the form: $x^i + y^j$ where: i >= 0 j >= 0 the resulting value is less than or equal to bound The inputs are three integers: x , the base of the first exponential term y ,...
leetcode Medium hash-table math enumeration May 28, 2026
Practice › LeetCode › LeetCode 08xx ›

LeetCode 829 - Consecutive Numbers Sum

LeetCode Problem 829 Difficulty: 🔴 Hard Topics: Math, Enumeration Solution Problem Understanding The problem asks us to determine in how many distinct ways an integer n can be expressed as a sum of consecutive positive integers. In other words, we need to find sequences of integers starting from some positive number x and having length k such that the sum of that sequence equals n . The sequences must consist...
leetcode Hard math enumeration May 28, 2026
Practice › LeetCode › LeetCode 08xx ›

LeetCode 869 - Reordered Power of 2

LeetCode Problem 869 Difficulty: 🟡 Medium Topics: Hash Table, Math, Sorting, Counting, Enumeration Solution Problem Understanding The problem gives us a positive integer n and asks whether its digits can be rearranged to form a power of two. The rearrangement may keep the digits in their original order or place them in any other order, but the resulting number cannot contain a leading zero. A power of two is any...
leetcode Medium hash-table math sorting counting enumeration May 28, 2026
Practice › LeetCode › LeetCode 08xx ›

LeetCode 845 - Longest Mountain in Array

LeetCode Problem 845 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Dynamic Programming, Enumeration Solution Problem Understanding The problem asks us to find the length of the longest contiguous subarray that forms a valid mountain. A mountain is a sequence that strictly increases up to a peak, then strictly decreases afterward. The peak cannot be the first or last element of the subarray because the mountain must contain both an uphill...
leetcode Medium array two-pointers dynamic-programming enumeration May 28, 2026
Practice › LeetCode › LeetCode 16xx ›

LeetCode 1601 - Maximum Number of Achievable Transfer Requests

LeetCode Problem 1601 Difficulty: 🔴 Hard Topics: Array, Backtracking, Bit Manipulation, Enumeration Solution Problem Understanding The problem asks us to maximize the number of employee transfer requests that can be fulfilled under the constraint that the total number of employees in each building remains constant. Each request is represented as a pair [from, to] , indicating an employee wants to move from building from to building to . The challenge...
leetcode Hard array backtracking bit-manipulation enumeration May 28, 2026
Practice › LeetCode › LeetCode 15xx ›

LeetCode 1534 - Count Good Triplets

LeetCode Problem 1534 Difficulty: 🟢 Easy Topics: Array, Enumeration Solution Problem Understanding The problem asks us to count the number of good triplets in an integer array arr based on three difference constraints a , b , and c . A triplet (arr[i], arr[j], arr[k]) is considered good if it satisfies three conditions simultaneously: the indices i , j , and k are strictly increasing ( 0 <= i <...
leetcode Easy array enumeration May 28, 2026
Practice › LeetCode › LeetCode 02xx ›

LeetCode 204 - Count Primes

LeetCode Problem 204 Difficulty: 🟡 Medium Topics: Array, Math, Enumeration, Number Theory Solution Problem Understanding The problem asks us to count how many prime numbers exist that are strictly smaller than a given integer n . A prime number is a positive integer greater than 1 that has exactly two divisors: 1 and itself. Examples of prime numbers include 2 , 3 , 5 , 7 , and 11 ....
leetcode Medium array math enumeration number-theory May 27, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 970: Powerful Integers

Problem Restatement We are given three integers: x y bound An integer is powerful if it can be written as: x ** i + y ** j where: i >= 0 j >= 0 Return all powerful integers less than or equal to bound . Each value should appear at most once, and the answer may be returned in any order. The constraints are 1 <= x, y <= 100...
leetcode math hash-table enumeration May 12, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 816: Ambiguous Coordinates

Problem Restatement We are given a string s that represents a coordinate pair after removing commas, spaces, and decimal points. For example: "(1, 3)" -> "(13)" "(2, 0.5)" -> "(205)" The string still contains the opening and closing parentheses. We need to return all possible original coordinate strings. The original coordinate representation had no unnecessary zeroes. So values like these are invalid: "00" "001" "0.0" "1.0" ".1" The final answer...
leetcode string enumeration backtracking May 12, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 906: Super Palindromes

Problem Restatement A positive integer is called a super-palindrome if: The number itself is a palindrome. It is the square of another palindrome. We are given two positive integers left and right as strings. Return how many super-palindromes are in the inclusive range: [left, right] For example, 9 is a super-palindrome because: 9 = 3 * 3 and both 9 and 3 are palindromes. The official problem uses string inputs...
leetcode math palindrome enumeration May 12, 2026
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...
leetcode string simulation enumeration May 12, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 555: Split Concatenated Strings

Problem Restatement We are given an array of strings strs . We can concatenate the strings into a loop. For each string, we may use it normally or reversed. The strings must stay in the same order as given. After forming the loop, we choose one cut point. Cutting the loop turns it into a normal string. Our goal is to return the lexicographically largest possible string. The input strings...
leetcode string greedy enumeration May 11, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 411: Minimum Unique Word Abbreviation

Problem Restatement We are given a target string and a dictionary of strings. We need to find the shortest abbreviation of target that does not conflict with any abbreviation of any word in the dictionary. An abbreviation may replace substrings with their lengths. Each number or letter in the abbreviation counts as length 1 . For example, "a32bc" has abbreviation length 4 . If multiple shortest answers exist, any one...
leetcode bit-manipulation backtracking string enumeration May 10, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 03xx ›

LeetCode 306: Additive Number

Problem Restatement We are given a string num containing only digits. Return true if the digits can be split into an additive sequence. Otherwise, return false . An additive sequence must satisfy three rules: Rule Meaning At least three numbers We need a, b, c , not only a, b Sum rule Every number after the first two equals the sum of the previous two No leading zeros Numbers like...
leetcode string backtracking enumeration May 10, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 479: Largest Palindrome Product

Problem Restatement We are given an integer n . We need to find the largest palindrome that can be written as the product of two n -digit integers. Because the answer may be very large, we return the palindrome modulo 1337 . For example, when n = 2 , the two-digit numbers are from 10 to 99 . The largest palindrome product is: 99 * 91 = 9009 Then we...
leetcode math enumeration palindrome May 10, 2026
Practice › LeetCode › LeetCode (archived) › LeetCode 04xx ›

LeetCode 401: Binary Watch

Problem Restatement A binary watch uses LEDs to show time. There are 4 LEDs for the hour. The hour range is: 0 <= hour <= 11 There are 6 LEDs for the minute. The minute range is: 0 <= minute <= 59 Each LED represents one binary bit. A bit with value 1 means the LED is on. Given an integer turnedOn , return all possible valid times where exactly...
leetcode bit-manipulation enumeration binary-watch May 10, 2026