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Practice › LeetCode › LeetCode 36xx ›

LeetCode 3669 - Balanced K-Factor Decomposition

LeetCode Problem 3669 Difficulty: 🟡 Medium Topics: Math, Backtracking, Number Theory Solution Problem Understanding We are given two integers, n and k . Our goal is to split n into exactly k positive integers whose product is equal to n . Among all valid decompositions, we want the one where the difference between the largest number and the smallest number is as small as possible. Since the maximum difference between...

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...

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3646 - Next Special Palindrome Number

LeetCode Problem 3646 Difficulty: 🔴 Hard Topics: Backtracking, Bit Manipulation Solution Problem Understanding This problem asks us to construct a number system under two simultaneous constraints and then perform a “next greater element” query over that constrained set. We are given an integer n , and we must find the smallest integer strictly greater than n such that the number satisfies a special structural property. A number is considered special...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3437 - Permutations III

LeetCode Problem 3437 Difficulty: 🟡 Medium Topics: Array, Backtracking Solution LeetCode 3437 - Permutations III Problem Understanding We are given a single integer n , and we need to generate all permutations of the numbers from 1 to n . However, not every permutation is valid. A permutation is considered an alternating permutation if every pair of adjacent elements has different parity. In other words: An odd number must always...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3376 - Minimum Time to Break Locks I

LeetCode Problem 3376 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Breadth-First Search, Bitmask Solution LeetCode 3376 - Minimum Time to Break Locks I Problem Understanding The problem describes a sequence of locks that must all be broken. Each lock requires a certain amount of energy, given by strength[i] . Bob's sword starts with: Energy = 0 Growth factor x = 1 Every minute, the sword gains x...

Practice › LeetCode › LeetCode 20xx ›

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...

Practice › LeetCode › LeetCode 23xx ›

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,...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2698 - Find the Punishment Number of an Integer

LeetCode Problem 2698 Difficulty: 🟡 Medium Topics: Math, Backtracking Solution Problem Understanding The problem asks us to compute a special value called the punishment number for a given integer n . For every integer i in the range [1, n] , we square the number and examine the decimal representation of i * i . The key question is whether we can split this decimal string into contiguous pieces such...

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...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2992 - Number of Self-Divisible Permutations

LeetCode Problem 2992 Difficulty: 🟡 Medium Topics: Array, Math, Dynamic Programming, Backtracking, Bit Manipulation, Number Theory, Bitmask Solution Problem Understanding The problem asks us to count how many permutations of the numbers 1 through n satisfy a special condition called self-divisible. We start with the array: [1, 2, 3, ..., n] We must rearrange these numbers into every possible permutation, then determine whether the permutation is valid. A permutation a...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2597 - The Number of Beautiful Subsets

LeetCode Problem 2597 Difficulty: 🟡 Medium Topics: Array, Hash Table, Math, Dynamic Programming, Backtracking, Sorting, Combinatorics Solution Problem Understanding The problem asks us to count how many non-empty subsets of the array nums are considered "beautiful". A subset is beautiful if there are no two numbers inside the subset whose absolute difference equals k . For example, if k = 2 , then the subset cannot contain both 2 and...

Practice › LeetCode › LeetCode 22xx ›

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...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3211 - Generate Binary Strings Without Adjacent Zeros

LeetCode Problem 3211 Difficulty: 🟡 Medium Topics: String, Backtracking, Bit Manipulation Solution Problem Understanding The problem asks us to generate every binary string of length n such that no substring of length 2 contains two consecutive zeros. A binary string contains only the characters "0" and "1" . A substring of length 2 means every adjacent pair of characters in the string. The condition says that every such pair must...

Practice › LeetCode › LeetCode 21xx ›

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 ,...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2152 - Minimum Number of Lines to Cover Points

LeetCode Problem 2152 Difficulty: 🟡 Medium Topics: Array, Hash Table, Math, Dynamic Programming, Backtracking, Bit Manipulation, Geometry, Bitmask Solution Problem Understanding This problem asks us to determine the minimum number of straight lines needed to cover a given set of points on an X-Y plane. Each point is defined by its (x, y) coordinates, and a straight line can pass through any number of points as long as they are...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2305 - Fair Distribution of Cookies

LeetCode Problem 2305 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem asks us to distribute a set of cookie bags among k children such that the unfairness of the distribution is minimized. Here, unfairness is defined as the maximum total number of cookies any single child receives . The input consists of an array cookies where cookies[i] represents the number of cookies...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1863 - Sum of All Subset XOR Totals

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

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2850 - Minimum Moves to Spread Stones Over Grid

LeetCode Problem 2850 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Matrix, Bitmask Solution Problem Understanding This problem asks us to take a 3x3 grid of integers representing stones in each cell and redistribute them so that every cell contains exactly one stone. Each move consists of moving a stone from one cell to a directly adjacent cell (sharing a side, not a diagonal). The goal is to...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2375 - Construct Smallest Number From DI String

LeetCode Problem 2375 Difficulty: 🟡 Medium Topics: String, Backtracking, Stack, Greedy Solution Problem Understanding The problem asks us to construct the lexicographically smallest number from a string pattern consisting of 'I' and 'D' . Each character in the pattern defines a relationship between consecutive digits of the number: 'I' indicates that the next digit should be larger than the current, and 'D' indicates the next digit should be smaller ....

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1986 - Minimum Number of Work Sessions to Finish the Tasks

LeetCode Problem 1986 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding This problem asks us to schedule a collection of tasks into the minimum number of work sessions. Each task has a fixed duration, and every work session has a maximum allowed length, sessionTime . A task cannot be split across multiple sessions. Once a task starts inside a session, it must fully complete...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2065 - Maximum Path Quality of a Graph

LeetCode Problem 2065 Difficulty: 🔴 Hard Topics: Array, Backtracking, Graph Theory Solution Problem Understanding We are given an undirected weighted graph where each node has an associated value. A path is considered valid if: It starts at node 0 It ends at node 0 The total travel time does not exceed maxTime The important detail is that nodes may be revisited multiple times, but each node's value contributes to the...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2664 - The Knight’s Tour

LeetCode Problem 2664 Difficulty: 🟡 Medium Topics: Array, Backtracking, Matrix Solution LeetCode 2664 - The Knight’s Tour Problem Understanding This problem asks us to construct a complete knight’s tour on an m x n chessboard. A knight’s tour is a sequence of knight moves such that every cell on the board is visited exactly once. We are given: m , the number of rows n , the number of columns...

Practice › LeetCode › LeetCode 20xx ›

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...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3348 - Smallest Divisible Digit Product II

LeetCode Problem 3348 Difficulty: 🔴 Hard Topics: Math, String, Backtracking, Greedy, Number Theory Solution Problem Understanding The problem asks us to find the smallest number that satisfies several constraints relative to a given number num and a target integer t . The input num is a string representing a positive integer, and the number must be zero-free , meaning none of its digits are zero. Additionally, the product of its...

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...

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 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...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2178 - Maximum Split of Positive Even Integers

LeetCode Problem 2178 Difficulty: 🟡 Medium Topics: Math, Backtracking, Greedy Solution Problem Understanding The problem is asking us to take an input integer finalSum and split it into the maximum number of unique positive even integers such that their sum equals finalSum . A unique positive even integer means each number in the split must be even, greater than zero, and cannot be repeated. If no valid split exists (for...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1947 - Maximum Compatibility Score Sum

LeetCode Problem 1947 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem is asking us to optimally pair students with mentors such that the sum of their compatibility scores is maximized. Each student and each mentor has answered n yes/no questions represented by 0 s and 1 s. A student-mentor pair's compatibility score is the count of matching answers. For instance, if a...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2767 - Partition String Into Minimum Beautiful Substrings

LeetCode Problem 2767 Difficulty: 🟡 Medium Topics: Hash Table, String, Dynamic Programming, Backtracking Solution Problem Understanding The problem asks us to partition a given binary string s into the minimum number of substrings such that each substring is beautiful . A substring is beautiful if it represents a power of 5 in decimal and does not have leading zeros. The string s contains only '0' and '1' characters, and its...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1980 - Find Unique Binary String

LeetCode Problem 1980 Difficulty: 🟡 Medium Topics: Array, Hash Table, String, Backtracking Solution Problem Understanding The problem is asking us to find a binary string of length n that does not exist in a given list nums of unique binary strings, where each string in nums also has length n . In simpler terms, we are given n strings that consist of 0s and 1s, and we need to generate...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 473 - Matchsticks to Square

LeetCode Problem 473 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution LeetCode 473 - Matchsticks to Square Problem Understanding The problem gives us an array called matchsticks , where each element represents the length of a matchstick. The goal is to determine whether all of the matchsticks can be arranged to form exactly one square. A square has four equal sides, so the total length of...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 95 - Unique Binary Search Trees II

LeetCode Problem 95 Difficulty: 🟡 Medium Topics: Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to generate all structurally unique binary search trees (BSTs) that contain exactly n nodes labeled from 1 to n . A BST is a binary tree where for every node, all values in the left subtree are smaller than the node, and all values in the right...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 37 - Sudoku Solver

LeetCode Problem 37 Difficulty: 🔴 Hard Topics: Array, Hash Table, Backtracking, Matrix Solution Problem Understanding The problem asks us to build a complete Sudoku solver. We are given a partially filled 9 x 9 grid where each cell contains either a digit from '1' to '9' or the character '.' , which represents an empty space. Our goal is to fill every empty cell so that the final board satisfies...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 638 - Shopping Offers

LeetCode Problem 638 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Memoization, Bitmask Solution Problem Understanding This problem asks us to find the minimum cost to buy a set of items given individual prices and optional special offers. We are given three main inputs: an array price that specifies the unit price for each item, an array needs that specifies the exact number of each item we want...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1258 - Synonymous Sentences

LeetCode Problem 1258 Difficulty: 🟡 Medium Topics: Array, Hash Table, String, Backtracking, Sort, Union-Find Solution Problem Understanding This problem asks us to generate all possible synonymous variations of a given sentence based on a list of equivalent word pairs. Each synonym pair indicates that the two words can replace each other interchangeably. The output must include all possible sentences created by substituting words with their synonyms and must be sorted...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 254 - Factor Combinations

LeetCode Problem 254 Difficulty: 🟡 Medium Topics: Backtracking Solution Problem Understanding The problem asks us to generate every unique way to express a number n as a product of integers greater than 1 and less than n . A factor combination is a list of integers whose product equals n . The order inside a combination does not matter. For example, for 12 , the combinations [2, 6] and [6,...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 51 - N-Queens

LeetCode Problem 51 Difficulty: 🔴 Hard Topics: Array, Backtracking Solution Problem Understanding The N-Queens problem asks us to place n queens on an n x n chessboard such that no two queens can attack each other. In chess, a queen can attack horizontally, vertically, and diagonally. This means that for any valid arrangement: No two queens can share the same row No two queens can share the same column No...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 301 - Remove Invalid Parentheses

LeetCode Problem 301 Difficulty: 🔴 Hard Topics: String, Backtracking, Breadth-First Search Solution Problem Understanding The problem asks us to remove the minimum number of invalid parentheses from a string so that the remaining string becomes valid. The input string may contain lowercase English letters in addition to parentheses. Letters do not affect validity and should always remain in the resulting strings unless they are removed as part of a broader...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 465 - Optimal Account Balancing

LeetCode Problem 465 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem gives a list of money transfers between people. Each transaction is represented as [from, to, amount] , meaning one person paid a certain amount to another person. After all transactions are completed, some people may owe money overall, while others are owed money overall. The goal is not to recreate the...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 93 - Restore IP Addresses

LeetCode Problem 93 Difficulty: 🟡 Medium Topics: String, Backtracking Solution Problem Understanding The problem asks us to take a string containing only digits and determine every possible way to insert exactly three dots so that the resulting string becomes a valid IPv4 address. A valid IP address has four numeric segments separated by dots. Each segment must satisfy two conditions: Its numeric value must be between 0 and 255 inclusive....

Practice › LeetCode › LeetCode 06xx ›

LeetCode 679 - 24 Game

LeetCode Problem 679 Difficulty: 🔴 Hard Topics: Array, Math, Backtracking Solution Problem Understanding The problem is asking us to determine whether it is possible to use exactly four numbers, each between 1 and 9 inclusive, to form a mathematical expression that evaluates to exactly 24. The numbers are given in an array called cards of length 4. We can use the four basic arithmetic operations + , - , *...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 131 - Palindrome Partitioning

LeetCode Problem 131 Difficulty: 🟡 Medium Topics: String, Dynamic Programming, Backtracking Solution LeetCode 131, Palindrome Partitioning Problem Understanding The problem gives us a string s and asks us to divide it into substrings such that every substring is a palindrome. A palindrome is a string that reads the same forward and backward. We must return all possible valid ways to partition the string. A partition means splitting the string into...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1239 - Maximum Length of a Concatenated String with Unique Characters

LeetCode Problem 1239 Difficulty: 🟡 Medium Topics: Array, String, Backtracking, Bit Manipulation Solution Problem Understanding This problem asks us to select a subsequence of strings from the input array arr and concatenate them together such that the resulting string contains only unique characters. Among all valid concatenations, we must return the maximum possible length. A subsequence means we can either include or skip each string while preserving the original order....

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2002 - Maximum Product of the Length of Two Palindromic Subsequences

LeetCode Problem 2002 Difficulty: 🟡 Medium Topics: String, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem is asking us to find two disjoint palindromic subsequences from a given string s such that the product of their lengths is maximized. A subsequence is derived by deleting zero or more characters from the original string while keeping the relative order intact. A palindrome reads the same forward and backward,...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 411 - Minimum Unique Word Abbreviation

LeetCode Problem 411 Difficulty: 🔴 Hard Topics: Array, String, Backtracking, Bit Manipulation Solution LeetCode 411 - Minimum Unique Word Abbreviation Problem Understanding This problem asks us to generate the shortest possible abbreviation for a given target word such that the abbreviation cannot also represent any word in the dictionary. An abbreviation replaces one or more non-adjacent substrings with their lengths. For example, the word "apple" can become: "5" because the...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 90 - Subsets II

LeetCode Problem 90 Difficulty: 🟡 Medium Topics: Array, Backtracking, Bit Manipulation Solution Problem Understanding The problem asks us to generate every possible subset of a given integer array. A subset is any selection of elements from the array, including the empty subset and the subset containing all elements. Unlike the classic Subsets problem, this version introduces an important complication: the input array may contain duplicate values. Because of this, multiple...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 425 - Word Squares

LeetCode Problem 425 Difficulty: 🔴 Hard Topics: Array, String, Backtracking, Trie Solution Problem Understanding The problem is asking us to generate all possible word squares from a given list of unique words. A word square is a square arrangement of words such that the word at row i is identical to the word at column i for every i . In other words, reading across the rows and down the...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 79 - Word Search

LeetCode Problem 79 Difficulty: 🟡 Medium Topics: Array, String, Backtracking, Depth-First Search, Matrix Solution Problem Understanding In this problem, we are given a two dimensional grid of characters called board and a target string called word . The task is to determine whether the word can be formed by traversing the grid under a strict set of movement rules. A valid word construction must satisfy the following conditions: You may...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 491 - Non-decreasing Subsequences

LeetCode Problem 491 Difficulty: 🟡 Medium Topics: Array, Hash Table, Backtracking, Bit Manipulation Solution LeetCode 491 - Non-decreasing Subsequences Problem Understanding The problem gives us an integer array nums and asks us to return every distinct subsequence that is non-decreasing and has length at least two. A subsequence is formed by deleting zero or more elements from the array without changing the relative order of the remaining elements. Unlike subarrays,...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 140 - Word Break II

LeetCode Problem 140 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization Solution Problem Understanding The problem asks us to segment a given string s into all possible sentences where each word in the sentence exists in a given dictionary wordDict . Essentially, we need to find all ways to insert spaces into the string such that every resulting substring is a valid dictionary word. The...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1593 - Split a String Into the Max Number of Unique Substrings

LeetCode Problem 1593 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking Solution LeetCode 1593 - Split a String Into the Max Number of Unique Substrings Problem Understanding This problem asks us to split a string into the largest possible number of substrings such that every substring is unique. The substrings must be contiguous pieces of the original string, and when combined in order, they must reconstruct the original string exactly....

Practice › LeetCode › LeetCode 05xx ›

LeetCode 526 - Beautiful Arrangement

LeetCode Problem 526 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem asks us to count how many permutations of the integers from 1 to n satisfy a special divisibility condition. A permutation is an arrangement of all numbers from 1 to n where every number appears exactly once. For example, when n = 3 , the possible permutations include [1,2,3] , [2,1,3]...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 489 - Robot Room Cleaner

LeetCode Problem 489 Difficulty: 🔴 Hard Topics: Backtracking, Interactive Solution Problem Understanding This problem is an interactive backtracking problem where we must control a robot without directly seeing the room layout. Unlike traditional grid traversal problems, we are not given access to the actual room matrix during execution. The only way to explore the environment is through the robot's API. The room is conceptually a binary grid: 1 represents an...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 294 - Flip Game II

LeetCode Problem 294 Difficulty: 🟡 Medium Topics: Math, Dynamic Programming, Backtracking, Memoization, Game Theory Solution Problem Understanding This problem describes a two-player impartial game played on a string consisting only of '+' and '-' characters. A valid move consists of selecting any pair of consecutive "++" characters and flipping them into "--" . The players alternate turns. If a player cannot make a valid move on their turn, they lose...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1774 - Closest Dessert Cost

LeetCode Problem 1774 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking Solution Problem Understanding The problem asks us to create a dessert using one ice cream base and zero or more toppings, with the additional restriction that each topping type can be used at most twice. Each base and topping has a cost, and our goal is to make a dessert whose total cost is as close as possible to...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 698 - Partition to K Equal Sum Subsets

LeetCode Problem 698 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Memoization, Bitmask Solution Problem Understanding The problem is asking whether an array of integers nums can be divided into exactly k subsets such that each subset has the same sum. The input consists of the integer array nums and the integer k . The expected output is a boolean value: true if such a partitioning is possible,...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 996 - Number of Squareful Arrays

LeetCode Problem 996 Difficulty: 🔴 Hard Topics: Array, Hash Table, Math, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem asks us to count all permutations of a given integer array nums such that the array is squareful , meaning that the sum of every pair of adjacent elements is a perfect square . In other words, for a permutation [a1, a2, a3, ..., an] , each a[i]...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 357 - Count Numbers with Unique Digits

LeetCode Problem 357 Difficulty: 🟡 Medium Topics: Math, Dynamic Programming, Backtracking Solution Problem Understanding The problem asks us to count how many integers in the range 0 <= x < 10^n contain no repeated digits. For example, when n = 2 , the valid range is: 0 <= x < 100 This means we consider every number from 0 to 99 . Among these numbers, we only count those whose...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1655 - Distribute Repeating Integers

LeetCode Problem 1655 Difficulty: 🔴 Hard Topics: Array, Hash Table, Dynamic Programming, Backtracking, Bit Manipulation, Counting, Bitmask Solution Problem Understanding This problem asks whether we can satisfy a set of customer requests using repeated integers from the array nums . Each customer wants a certain quantity of numbers, given by quantity[i] . The important restriction is that every number given to a single customer must be identical. A customer asking...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 78 - Subsets

LeetCode Problem 78 Difficulty: 🟡 Medium Topics: Array, Backtracking, Bit Manipulation Solution LeetCode 78, Subsets Problem Understanding This problem asks us to generate every possible subset of a given array of unique integers. A subset is any selection of elements from the array, including the empty subset and the subset containing every element. If the input array has n elements, then there are exactly 2^n possible subsets. This comes from...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 980 - Unique Paths III

LeetCode Problem 980 Difficulty: 🔴 Hard Topics: Array, Backtracking, Bit Manipulation, Matrix Solution Problem Understanding This problem asks us to count the number of valid paths in a grid under very strict movement rules. We are given a matrix where each cell has a special meaning: 1 is the starting position 2 is the ending position 0 is an empty square we may walk on -1 is an obstacle that...

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...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 257 - Binary Tree Paths

LeetCode Problem 257 Difficulty: 🟢 Easy Topics: String, Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to return every path from the root of a binary tree to each leaf node. A root-to-leaf path is formed by starting at the root node and continuously moving downward through child nodes until reaching a node that has no children. The input is the root node of a...

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LeetCode 1096 - Brace Expansion II

LeetCode Problem 1096 Difficulty: 🔴 Hard Topics: Hash Table, String, Backtracking, Stack, Breadth-First Search, Sorting Solution Problem Understanding The problem asks us to interpret a string expression representing a set of words generated according to a specific grammar and return all distinct words sorted in lexicographical order. The expression can contain lowercase letters, curly braces {} , and commas , . The rules of the grammar are: A single lowercase...

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LeetCode 22 - Generate Parentheses

LeetCode Problem 22 Difficulty: 🟡 Medium Topics: String, Dynamic Programming, Backtracking Solution Problem Understanding The problem asks us to generate every possible valid combination of n pairs of parentheses. A valid parentheses string is one where every opening parenthesis ( has a matching closing parenthesis ) , and the parentheses are properly nested. For example, "(()())" is valid because every opening bracket is closed in the correct order. However, strings...

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LeetCode 40 - Combination Sum II

LeetCode Problem 40 Difficulty: 🟡 Medium Topics: Array, Backtracking Solution Problem Understanding This problem asks us to find all unique combinations of numbers from the candidates array such that the sum of the chosen numbers equals target . Unlike the original Combination Sum problem, each number can only be used once. Even if a number appears multiple times in the input array, each occurrence is treated as a separate element,...

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LeetCode 46 - Permutations

LeetCode Problem 46 Difficulty: 🟡 Medium Topics: Array, Backtracking Solution LeetCode 46 - Permutations Problem Understanding The problem gives us an array of distinct integers called nums , and asks us to generate every possible permutation of those numbers. A permutation is an arrangement of elements in a specific order. For example, if the input is [1,2,3] , then [1,2,3] , [1,3,2] , and [2,1,3] are all different permutations because...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 842 - Split Array into Fibonacci Sequence

LeetCode Problem 842 Difficulty: 🟡 Medium Topics: String, Backtracking Solution LeetCode 842 - Split Array into Fibonacci Sequence Problem Understanding The problem gives us a string consisting only of digits, and asks us to split it into a sequence of integers that behaves like a Fibonacci sequence. A Fibonacci-like sequence follows three important rules: Every number must fit inside a signed 32-bit integer, meaning each value must be less than...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1467 - Probability of a Two Boxes Having The Same Number of Distinct Balls

LeetCode Problem 1467 Difficulty: 🔴 Hard Topics: Array, Math, Dynamic Programming, Backtracking, Combinatorics, Probability and Statistics Solution Problem Understanding The problem gives us several colors of balls, where balls[i] represents how many balls exist for color i . The total number of balls is always even, say 2n . We randomly shuffle all balls and place the first n balls into box 1 and the remaining n balls into box...

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LeetCode 1238 - Circular Permutation in Binary Representation

LeetCode Problem 1238 Difficulty: 🟡 Medium Topics: Math, Backtracking, Bit Manipulation Solution LeetCode 1238 - Circular Permutation in Binary Representation Problem Understanding This problem asks us to construct a special ordering of all integers from 0 to 2^n - 1 . The ordering must satisfy the properties of a circular Gray code sequence. We are given two integers: n , which determines how many numbers exist in the permutation start...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1079 - Letter Tile Possibilities

LeetCode Problem 1079 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking, Counting Solution Problem Understanding The problem asks us to count all possible non-empty sequences that can be formed from a set of letter tiles, where each tile has a single uppercase letter. The input is a string tiles representing the letters available on the tiles. The output is an integer representing the total number of distinct sequences that can...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 494 - Target Sum

LeetCode Problem 494 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking Solution Problem Understanding The problem asks us to count how many different ways we can assign either a '+' or '-' sign to every number in the array nums such that the resulting arithmetic expression evaluates to target . Each number must be used exactly once, and for every position we have only two choices: Add the number Subtract...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1799 - Maximize Score After N Operations

LeetCode Problem 1799 Difficulty: 🔴 Hard Topics: Array, Math, Dynamic Programming, Backtracking, Bit Manipulation, Number Theory, Bitmask Solution Problem Understanding The problem asks us to maximize the total score obtained by performing n operations on an array nums of size 2 * n . In each operation, you select two elements from the array, calculate the greatest common divisor (GCD) of the two elements, multiply it by the operation index...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 784 - Letter Case Permutation

LeetCode Problem 784 Difficulty: 🟡 Medium Topics: String, Backtracking, Bit Manipulation Solution Problem Understanding The problem asks us to generate every possible string that can be formed by independently changing the case of each alphabetic character in the input string. Digits cannot be modified, so they always remain the same in every generated result. Only English letters can change between lowercase and uppercase. For example, if the input is "a1b2"...

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LeetCode 17 - Letter Combinations of a Phone Number

LeetCode Problem 17 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking Solution Problem Understanding The problem gives a string of digits where each digit is between 2 and 9 . Each digit corresponds to a set of letters on a traditional phone keypad: 2 -> "abc" 3 -> "def" 4 -> "ghi" 5 -> "jkl" 6 -> "mno" 7 -> "pqrs" 8 -> "tuv" 9 -> "wxyz" We must generate...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1219 - Path with Maximum Gold

LeetCode Problem 1219 Difficulty: 🟡 Medium Topics: Array, Backtracking, Matrix Solution Problem Understanding The problem gives us a two dimensional grid representing a gold mine. Each cell contains either a positive amount of gold or 0 , which means the cell is empty. We are allowed to start from any cell that contains gold and move through the grid collecting gold along the way. Movement is restricted to the four...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1088 - Confusing Number II

LeetCode Problem 1088 Difficulty: 🔴 Hard Topics: Math, Backtracking Solution Problem Understanding In this problem, we are given an integer n , and we must count how many numbers in the range [1, n] are considered confusing numbers. A number becomes a confusing number if, after rotating every digit by 180 degrees, the resulting number is both: Valid after rotation Different from the original number Only five digits remain valid...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 401 - Binary Watch

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

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1240 - Tiling a Rectangle with the Fewest Squares

LeetCode Problem 1240 Difficulty: 🔴 Hard Topics: Backtracking Solution Problem Understanding The problem is asking us to completely cover a rectangle of size n x m with the fewest number of squares that have integer side lengths. The rectangle can be tiled with squares of any size, as long as each square fits entirely within the rectangle and there is no overlap. The input consists of two integers, n and...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 320 - Generalized Abbreviation

LeetCode Problem 320 Difficulty: 🟡 Medium Topics: String, Backtracking, Bit Manipulation Solution LeetCode 320, Generalized Abbreviation Problem Understanding This problem asks us to generate every possible generalized abbreviation of a given word. A generalized abbreviation is created by replacing some characters in the string with their count, while preserving the order of the remaining characters. The important restriction is that abbreviated sections must be non-overlapping and non-adjacent. In practice, this...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1415 - The k-th Lexicographical String of All Happy Strings of Length n

LeetCode Problem 1415 Difficulty: 🟡 Medium Topics: String, Backtracking Solution LeetCode 1415, The k-th Lexicographical String of All Happy Strings of Length n Problem Understanding The problem asks us to generate strings of length n using only the characters 'a' , 'b' , and 'c' , with one important restriction: no two adjacent characters can be the same. These valid strings are called happy strings. After generating all valid happy...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1255 - Maximum Score Words Formed by Letters

LeetCode Problem 1255 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Dynamic Programming, Backtracking, Bit Manipulation, Counting, Bitmask Solution Problem Understanding This problem asks us to select a subset of words that can be constructed using a limited supply of letters, such that the total score of all chosen words is maximized. We are given three inputs: words , an array of strings letters , a multiset of available characters...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 267 - Palindrome Permutation II

LeetCode Problem 267 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking Solution Problem Understanding The problem asks us to generate every unique palindrome that can be formed by rearranging the characters of a given string. A palindrome is a string that reads the same forward and backward. For example, "abba" and "racecar" are palindromes. The task is not to determine whether the original string is already a palindrome. Instead, we...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1066 - Campus Bikes II

LeetCode Problem 1066 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution That is a long-form technical guide with multiple required sections and detailed worked examples. I can provide the complete reference document, but it will be quite lengthy. I will include all requested sections: Problem Understanding Brute Force and Optimal Approaches Comparison Table Step-by-step Algorithm Walkthrough with proof sketch Complete Python Solution Complete Go Solution Fully...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 967 - Numbers With Same Consecutive Differences

LeetCode Problem 967 Difficulty: 🟡 Medium Topics: Backtracking, Breadth-First Search Solution Problem Understanding The problem asks us to generate all integers of length n such that the absolute difference between every two consecutive digits is exactly k . The input consists of two integers: n , the number of digits the integers must have, and k , the difference constraint between consecutive digits. The output is an array of integers...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 797 - All Paths From Source to Target

LeetCode Problem 797 Difficulty: 🟡 Medium Topics: Backtracking, Depth-First Search, Breadth-First Search, Graph Theory Solution Problem Understanding The problem gives us a directed acyclic graph, usually abbreviated as a DAG. The graph contains n nodes labeled from 0 to n - 1 . The graph is represented as an adjacency list, where graph[i] contains all nodes that can be reached directly from node i . Our task is to find...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1723 - Find Minimum Time to Finish All Jobs

LeetCode Problem 1723 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding This problem is asking us to assign a set of jobs, each with a specific time requirement, to k workers such that every job is assigned to exactly one worker, and we minimize the maximum total working time among all workers. The input jobs is an integer array where jobs[i] represents the time...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1307 - Verbal Arithmetic Puzzle

LeetCode Problem 1307 Difficulty: 🔴 Hard Topics: Array, Math, String, Backtracking Solution Problem Understanding The problem gives a collection of words on the left side of an equation and a single result word on the right side. Each distinct uppercase letter must be assigned a unique digit from 0 to 9 . After replacing every letter with its assigned digit, the numerical values represented by the left-side words must sum...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1215 - Stepping Numbers

LeetCode Problem 1215 Difficulty: 🟡 Medium Topics: Math, Backtracking, Breadth-First Search Solution Problem Understanding The problem is asking us to find all integers within a given range [low, high] that are stepping numbers . A stepping number is defined as a number in which the absolute difference between every pair of adjacent digits is exactly 1 . For instance, 321 is a stepping number because |3-2| = 1 and |2-1|...

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...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1087 - Brace Expansion

LeetCode Problem 1087 Difficulty: 🟡 Medium Topics: String, Backtracking, Stack, Breadth-First Search, Sorting Solution Problem Understanding In this problem, we are given a string that represents multiple possible words. Each position in the word may contain either a single fixed character or a set of alternative characters enclosed in curly braces. For example: a{b,c}d means: The first character is always 'a' The second character can be either 'b' or 'c'...

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,...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 988 - Smallest String Starting From Leaf

LeetCode Problem 988 Difficulty: 🟡 Medium Topics: String, Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree where every node stores an integer between 0 and 25 . Each integer corresponds to a lowercase English letter: 0 -> 'a' 1 -> 'b' ... 25 -> 'z' We need to construct strings that begin at a leaf node and move upward...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 77 - Combinations

LeetCode Problem 77 Difficulty: 🟡 Medium Topics: Backtracking Solution Problem Understanding This problem asks us to generate all possible combinations of size k from the numbers in the inclusive range [1, n] . In other words, we are given two integers: n , which defines the range of available numbers from 1 to n k , which specifies how many numbers each combination must contain The task is to return...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 773 - Sliding Puzzle

LeetCode Problem 773 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Backtracking, Breadth-First Search, Memoization, Matrix Solution Problem Understanding The Sliding Puzzle problem presents a 2 x 3 board containing five numbered tiles from 1 to 5 and a blank space represented as 0 . The goal is to transform the board into a solved configuration [[1,2,3],[4,5,0]] using the fewest number of moves, where a move consists of swapping 0 with...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 351 - Android Unlock Patterns

LeetCode Problem 351 Difficulty: 🟡 Medium Topics: Dynamic Programming, Backtracking, Bit Manipulation, Bitmask Solution Problem Understanding The problem models the Android lock screen as a 3 x 3 grid containing digits 1 through 9 . A valid unlock pattern is a sequence of distinct dots that follows a special movement rule. The first rule is straightforward: each dot can only be used once in a pattern. This means every pattern...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1286 - Iterator for Combination

LeetCode Problem 1286 Difficulty: 🟡 Medium Topics: String, Backtracking, Design, Iterator Solution Problem Understanding The problem asks us to design a class CombinationIterator that generates all combinations of a given length from a string of sorted, distinct lowercase letters. The iterator must return these combinations in lexicographical order , meaning alphabetically. The input consists of two components: a string characters , which contains unique letters sorted in ascending order, and...

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LeetCode 89 - Gray Code

LeetCode Problem 89 Difficulty: 🟡 Medium Topics: Math, Backtracking, Bit Manipulation Solution LeetCode 89 - Gray Code Problem Understanding The problem asks us to generate a valid Gray code sequence for a given number of bits, n . A Gray code sequence is a special ordering of numbers where every adjacent pair differs by exactly one bit in binary form. In addition, the sequence is cyclic, meaning the first and...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 212 - Word Search II

LeetCode Problem 212 Difficulty: 🔴 Hard Topics: Array, String, Backtracking, Trie, Matrix Solution Problem Understanding LeetCode 212, LeetCode Word Search II, asks us to find every word from a given dictionary that can be formed inside a 2D character grid. Each word must be built by moving one cell at a time horizontally or vertically. Diagonal movement is not allowed, and a board cell cannot be reused within the same...

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LeetCode 216 - Combination Sum III

LeetCode Problem 216 Difficulty: 🟡 Medium Topics: Array, Backtracking Solution Problem Understanding This problem asks us to generate all unique combinations of exactly k distinct numbers chosen from the range 1 to 9 such that their sum equals n . Each number can only be used once in a combination. This means combinations like [1,1,5] are invalid because the number 1 is repeated. Order also does not matter, so [1,2,4]...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 756 - Pyramid Transition Matrix

LeetCode Problem 756 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking, Bit Manipulation Solution Here’s a full, detailed technical solution guide for LeetCode 756 - Pyramid Transition Matrix , following your formatting rules precisely. Problem Understanding The problem is asking us to determine whether a pyramid of blocks can be constructed from a given bottom row of blocks, such that all blocks above obey certain triangular stacking rules. Each block...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 126 - Word Ladder II

LeetCode Problem 126 Difficulty: 🔴 Hard Topics: Hash Table, String, Backtracking, Breadth-First Search Solution Problem Understanding This problem asks us to find all shortest transformation sequences from beginWord to endWord , where each transformation changes exactly one character and every intermediate word must exist in wordList . We can think of the problem as navigating through a graph. Each word is a node, and two words are connected if they...

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...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 306 - Additive Number

LeetCode Problem 306 Difficulty: 🟡 Medium Topics: String, Backtracking Solution Problem Understanding The problem asks us to determine whether a given string of digits can be partitioned into a valid additive sequence. An additive sequence is a sequence of numbers where: There are at least three numbers. Every number after the first two is equal to the sum of the previous two numbers. No number is allowed to contain leading...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 52 - N-Queens II

LeetCode Problem 52 Difficulty: 🔴 Hard Topics: Backtracking Solution LeetCode 52, N-Queens II Problem Statement The n-queens puzzle asks us to place n queens on an n x n chessboard so that no two queens can attack each other. In chess, a queen can move horizontally, vertically, and diagonally. That means any two queens sharing the same row, same column, or same diagonal would be attacking one another, which is...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1718 - Construct the Lexicographically Largest Valid Sequence

LeetCode Problem 1718 Difficulty: 🟡 Medium Topics: Array, Backtracking Solution Problem Understanding The problem asks us to construct a special integer sequence using numbers from 1 to n . The resulting sequence has length 2 * n - 1 because: The number 1 appears exactly once. Every number from 2 to n appears exactly twice. That means the total number of elements is: 1 occurrence for 1 2 * (n...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 47 - Permutations II

LeetCode Problem 47 Difficulty: 🟡 Medium Topics: Array, Backtracking, Sorting Solution Problem Understanding The problem asks us to generate every possible permutation of the given array nums , while ensuring that duplicate permutations are not included in the final result. A permutation is an arrangement of all elements in a particular order. For example, the permutations of [1,2,3] are all six possible orderings of those three numbers. The complication in...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 282 - Expression Add Operators

LeetCode Problem 282 Difficulty: 🔴 Hard Topics: Math, String, Backtracking Solution Problem Understanding The problem gives us a numeric string num and an integer target . We must insert binary operators, specifically '+' , '-' , and '*' , between the digits of the string so that the resulting mathematical expression evaluates exactly to target . The important detail is that we are not allowed to reorder digits. We may...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 291 - Word Pattern II

LeetCode Problem 291 Difficulty: 🟡 Medium Topics: Hash Table, String, Backtracking Solution Problem Understanding The problem asks us to determine whether a given string s can be formed by substituting each character in a pattern with a non-empty string , under a bijective mapping . Bijective means that every character maps to exactly one unique substring and no two characters map to the same substring. Essentially, each character in the...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 113 - Path Sum II

LeetCode Problem 113 Difficulty: 🟡 Medium Topics: Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find all root-to-leaf paths in a binary tree where the sum of the node values equals a given targetSum . A binary tree is provided through the root node, and every node contains an integer value. We are also given an integer targetSum . Our task is to explore...

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LeetCode 39 - Combination Sum

LeetCode Problem 39 Difficulty: 🟡 Medium Topics: Array, Backtracking Solution Problem Understanding This problem asks us to generate every possible unique combination of numbers from the given candidates array such that the sum of the chosen numbers equals target . There are several important details in the problem statement: Every number in candidates is distinct. Each number can be used an unlimited number of times. The output should contain only...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 691 - Stickers to Spell Word

LeetCode Problem 691 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Dynamic Programming, Backtracking, Bit Manipulation, Memoization, Bitmask Solution Let's dive deep into a detailed technical solution guide for LeetCode 691, following your formatting rules exactly. Problem Understanding The problem asks us to construct a target string using letters cut from an unlimited supply of given stickers, where each sticker is a lowercase word. You can reuse stickers multiple times...

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

LeetCode 1087: Brace Expansion

Problem Restatement We are given a string s representing a word with the following format: A single letter c means the set {c} . A brace expression {a,b,c,...} means choose one of the letters. Consecutive groups are concatenated. Return all strings generated by the pattern in sorted order. The official constraints state that 1 <= s.length <= 50 . Input and Output Item Meaning Input Pattern string s Output Sorted...

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

LeetCode 1079: Letter Tile Possibilities

Problem Restatement We have a set of tiles with letters on them. We need to return the number of possible non-empty sequences of letters using some or all of the tiles. Two sequences are the same if they use the same letters in the same order. The official constraints state that 1 <= tiles.length <= 7 and each tiles[i] is an uppercase English letter. Input and Output Item Meaning Input...

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

LeetCode 1088: Confusing Number II

Problem Restatement A confusing number rotated 180 degrees gives a different valid number (see LeetCode 1056). Valid digit rotations: 0→0 , 1→1 , 6→9 , 8→8 , 9→6 . We are given a positive integer n . Count all confusing numbers in [1, n] . The official constraints state that 1 <= n <= 10^9 . Input and Output Item Meaning Input Integer n Output Count of confusing numbers in...

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

LeetCode 1096: Brace Expansion II

Problem Restatement We are given a string expression representing a set of strings under a brace expansion language: A letter c represents the set {c} . {e1, e2, ...} represents the union of the sets. e1 e2 (concatenation) represents all strings formed by concatenating one from each. Return all strings in the resulting set in sorted order. The official constraints state that 1 <= expression.length <= 60 . Input and...

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

LeetCode 967: Numbers With Same Consecutive Differences

Problem Restatement We are given two integers: n k Return all integers with exactly n digits such that the absolute difference between every two consecutive digits is exactly k . Numbers must not have leading zeros. The answer may be returned in any order. The official constraints are: Constraint Value n 2 <= n <= 9 k 0 <= k <= 9 Source: LeetCode problem statement. Input and Output Item...

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

LeetCode 842: Split Array into Fibonacci Sequence

Problem Restatement We are given a string num containing only digits. We need to split it into a Fibonacci-like sequence. A valid Fibonacci-like sequence must satisfy these rules: Rule Meaning Length The sequence must contain at least 3 numbers Value limit Every number must fit in a 32-bit signed integer Fibonacci rule seq[i] + seq[i + 1] == seq[i + 2] Leading zero rule A number cannot have extra leading...

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

LeetCode 996: Number of Squareful Arrays

Problem Restatement We are given an integer array nums . An array is squareful if the sum of every pair of adjacent elements is a perfect square. We need to return the number of unique permutations of nums that are squareful. For example, if two adjacent values are 1 and 8 , then: 1 + 8 = 9 Since 9 is a perfect square, this adjacent pair is valid. The...

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

LeetCode 797: All Paths From Source to Target

Problem Restatement We are given a directed acyclic graph, also called a DAG. The graph has n nodes labeled: 0, 1, 2, ..., n - 1 The graph is represented as an adjacency list. graph[i] contains every node we can visit directly from node i . We need to return all possible paths from node 0 to node n - 1 , in any order. The graph is guaranteed to...

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...

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

LeetCode 47: Permutations II

Problem Restatement We are given an array nums that may contain duplicate numbers. We need to return all possible unique permutations in any order. A permutation is an ordering that uses every element exactly once. Since nums may contain duplicates, different index choices can produce the same value ordering. We must return each unique ordering only once. The official problem states: given a collection of numbers that might contain duplicates,...

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

LeetCode 46: Permutations

Problem Restatement We are given an array nums containing distinct integers. We need to return all possible permutations of the array. A permutation is one possible ordering of all elements. The answer may be returned in any order. The official problem states: given an array nums of distinct integers, return all possible permutations. Example: nums = [1, 2, 3] The possible permutations are: [ [1, 2, 3], [1, 3, 2],...

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

LeetCode 698: Partition to K Equal Sum Subsets

Problem Restatement We are given an integer array nums and an integer k . We need to return true if it is possible to divide nums into k non-empty subsets such that every subset has the same sum. Otherwise, return false . Each number must be used exactly once. The official constraints include 1 <= k <= nums.length <= 16 and positive integers in nums . ( leetcode.com ) Input...

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

LeetCode 784: Letter Case Permutation

Problem Restatement We are given a string s . Each alphabet letter may be changed independently to lowercase or uppercase. Digits must stay the same. Return all possible strings we can create. The output may be returned in any order. Input and Output Item Meaning Input A string s Output A list of all possible letter-case permutations Letters Can become lowercase or uppercase Digits Must stay unchanged Constraint 1 <=...

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LeetCode 638: Shopping Offers

Problem Restatement We are given item prices, special bundle offers, and the exact number of each item we need to buy. Each item i has an individual price: price[i] Each special offer contains quantities of items plus a final bundle price: special[j] = [count_item_0, count_item_1, ..., offer_price] We can use each special offer any number of times. The goal is to pay the minimum total cost while buying exactly the...

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LeetCode 756: Pyramid Transition Matrix

Problem Restatement We are given a bottom row of blocks. Each block has a color represented by one letter. We are also given a list of allowed triples. A triple has length 3 . For example: "ABC" means: A B C If two adjacent blocks are A and B , then we may place C on top of them. Starting from the given bottom row, we need to decide whether...

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LeetCode 980: Unique Paths III

Problem Restatement We are given an m x n grid. Each cell has one of four values: Value Meaning 1 Starting square 2 Ending square 0 Empty square we can walk over -1 Obstacle we cannot walk over There is exactly one starting square and exactly one ending square. We need to count how many 4-directional walks go from the start to the end while visiting every non-obstacle square exactly...

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LeetCode 679: 24 Game

Problem Restatement We are given exactly four cards. Each card contains an integer from 1 to 9 . We need to decide whether we can arrange all four numbers into a mathematical expression that evaluates to 24 . We may use: Allowed item Meaning + Addition - Subtraction * Multiplication / Real division Parentheses Control operation order There are also important restrictions: Rule Meaning Use every card exactly once All...

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LeetCode 526: Beautiful Arrangement

Problem Restatement We are given an integer n . There are n integers labeled from 1 to n . We need to count how many permutations of these numbers are beautiful. A permutation perm is beautiful if, for every position i , at least one of these is true: perm[i] % i == 0 or: i % perm[i] == 0 The permutation is 1-indexed. That means positions start from 1...

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LeetCode 425: Word Squares

Problem Restatement We are given an array of unique strings: words All words have the same length. Return all word squares that can be built from these words. The same word may be used multiple times. A word square is a list of words where the k th row and the k th column read the same string. The answer may be returned in any order. The source statement says...

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LeetCode 473: Matchsticks to Square

Problem Restatement We are given an integer array matchsticks . Each value represents the length of one matchstick. We must use every matchstick exactly once. We need to determine whether all matchsticks can form a square. A square has four sides of equal length, so the task is to divide the matchsticks into four groups with the same sum. The official problem asks whether the given matchsticks can make one...

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LeetCode 320: Generalized Abbreviation

Problem Restatement We are given a lowercase string word . Return all possible generalized abbreviations of word . A generalized abbreviation replaces any number of non-overlapping and non-adjacent substrings with their lengths. For example, "abcde" can become "a3e" , "1bcd1" , "5" , or "abcde" . The input length is at most 15 , and the answer can be returned in any order. Input and Output Item Meaning Input A...

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LeetCode 494: Target Sum

Problem Restatement We are given an integer array nums and an integer target . For every number in nums , we must choose one sign: Sign Meaning + Add this number - Subtract this number We need to count how many different sign assignments evaluate to target . For example: nums = [1, 1, 1, 1, 1] target = 3 There are five valid expressions: -1 + 1 + 1...

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LeetCode 491: Non-decreasing Subsequences

Problem Restatement We are given an integer array nums . We need to return all different non-decreasing subsequences with length at least 2 . A subsequence keeps the original order, but may skip elements. A sequence is non-decreasing if every next value is greater than or equal to the previous value. The answer can be returned in any order. The constraints are 1 <= nums.length <= 15 and -100 <=...

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LeetCode 465: Optimal Account Balancing

Problem Restatement We are given a list of transactions. Each transaction has the form: [from_person, to_person, amount] This means from_person gave amount dollars to to_person . After all original transactions, some people may owe money and some people may be owed money. We need to return the minimum number of transactions required to settle all debts. The official problem defines each transaction as [from_i, to_i, amount_i] and asks for the...

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LeetCode 294: Flip Game II

Problem Restatement We are given a string currentState containing only: "+" "-" Two players take turns. On each turn, a player chooses two consecutive plus signs: "++" and flips them into: "--" The player who cannot make a move loses. We start first. We need to return whether the starting player can guarantee a win. The source statement defines the game this way: players take turns flipping two consecutive "++"...

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LeetCode 291: Word Pattern II

Problem Restatement We are given: pattern s We need to check whether s follows pattern . Each character in pattern must map to a non-empty substring of s . The mapping must be bijective: Rule Meaning One character maps to one substring The same pattern character must always use the same substring One substring maps to one character Two different pattern characters cannot use the same substring Full match All...

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LeetCode 216: Combination Sum III

Problem Restatement We are given two integers: k n We need to find all valid combinations of exactly k numbers that sum to n . Rules: Rule Meaning Number range Only numbers 1 through 9 may be used Reuse Each number can be used at most once Combination size Each combination must contain exactly k numbers Combination sum The numbers must add up to n Duplicates The answer must not...

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LeetCode 267: Palindrome Permutation II

Problem Restatement We are given a string s . Return all palindromic permutations of s without duplicates. A palindrome reads the same forward and backward. If no palindromic permutation exists, return an empty list. The answer may be returned in any order. The constraints are 1 <= s.length <= 16 , and s contains only lowercase English letters. Input and Output Item Meaning Input A lowercase string s Output List...

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LeetCode 95: Unique Binary Search Trees II

Problem Restatement We are given an integer n . We need to generate all structurally unique binary search trees that contain exactly the values: 1, 2, 3, ..., n Each value must be used exactly once. The answer may be returned in any order. A binary search tree has this rule: Node relation Required value rule Left subtree Values smaller than the root Right subtree Values greater than the root...

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LeetCode 93: Restore IP Addresses

Problem Restatement We are given a string s containing only digits. We need to return all possible valid IP addresses that can be formed by inserting dots into s . We cannot reorder digits. We cannot remove digits. We only insert exactly three dots so that the string becomes four valid IP address segments. A valid IP address has exactly four integers separated by dots. Each integer must be between...

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LeetCode 90: Subsets II

Problem Restatement We are given an integer array nums . Unlike LeetCode 78, this array may contain duplicate values. We need to return all possible subsets, also called the power set. The answer must not contain duplicate subsets. The subsets may be returned in any order. The official statement says that nums may contain duplicates, the solution set must not contain duplicate subsets, and the constraints are 1 <= nums.length...

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LeetCode 113: Path Sum II

Problem Restatement We are given the root of a binary tree and an integer targetSum . We need to return all root-to-leaf paths where the sum of node values equals targetSum . Each returned path must: Start at the root. End at a leaf. Have node values summing to targetSum . The official problem asks for all root-to-leaf paths whose sum equals the target. For this tree: 5 / \...

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LeetCode 89: Gray Code

Problem Restatement We are given an integer n . We need to return any valid n -bit Gray code sequence. A valid Gray code sequence has these rules: Rule Meaning Length The sequence contains 2^n integers Range Every integer is between 0 and 2^n - 1 Start The first integer must be 0 No duplicates Each integer appears at most once Adjacent rule Adjacent integers differ by exactly one bit...

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LeetCode 140: Word Break II

Problem Restatement We are given: Name Meaning s A string without spaces wordDict A list of valid dictionary words We need to insert spaces into s so that every piece is a valid dictionary word. Return all possible valid sentences. The same dictionary word may be reused multiple times. The answer may be returned in any order. LeetCode gives constraints including 1 <= s.length <= 20 , 1 <= wordDict.length...

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LeetCode 40: Combination Sum II

Problem Restatement We are given an array candidates and an integer target . We need to return all unique combinations where the chosen numbers sum to target . Each number in candidates may be used at most once. The input may contain duplicate values, but the answer must not contain duplicate combinations. The result may be returned in any order. The constraints are 1 <= candidates.length <= 100 , 1...

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LeetCode 212: Word Search II

Problem Restatement We are given: board words board is an m x n grid of characters. words is a list of strings. We need to return all words from words that can be formed on the board. A word can be formed by moving from one cell to another adjacent cell. Allowed moves: up down left right Diagonal moves are not allowed. The same board cell cannot be used more...

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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...

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LeetCode 39: Combination Sum

Problem Restatement We are given an array of distinct integers candidates and an integer target . We need to return all unique combinations of numbers from candidates whose sum equals target . Each candidate number may be chosen unlimited times. Two combinations are considered different only when the frequency of at least one chosen number is different. The result may be returned in any order. The test cases guarantee fewer...

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LeetCode 211: Design Add and Search Words Data Structure

Problem Restatement We need to design a data structure that supports two operations: Operation Meaning addWord(word) Add a word into the data structure search(word) Return whether a word matches the query The search query may contain lowercase letters and the special character: . A dot matches any one lowercase letter. The official LeetCode problem asks us to implement WordDictionary with addWord and search , where search supports . as a...

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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...

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LeetCode 488: Zuma Game

Problem Restatement We are given a row of colored balls called board and some balls in our hand called hand . Each ball has one of five colors: Character Color R Red Y Yellow B Blue G Green W White On each move, we choose one ball from hand and insert it anywhere in board . After insertion, if there are three or more consecutive balls of the same color,...

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LeetCode 37: Sudoku Solver

Problem Restatement We are given a partially filled 9 x 9 Sudoku board. Empty cells are represented by: "." We must fill the empty cells so that the final board satisfies Sudoku rules: Rule Meaning Row rule Each digit 1 to 9 appears exactly once in every row Column rule Each digit 1 to 9 appears exactly once in every column Box rule Each digit 1 to 9 appears exactly...

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LeetCode 282: Expression Add Operators

Problem Restatement We are given: A string num containing only digits. An integer target . We need to insert the operators: +, -, * between the digits so that the final mathematical expression evaluates exactly to target . We must return all valid expressions. Digits must remain in the original order. We may also choose to join consecutive digits into a larger number. For example: "123" can become: "1+2+3" "12-3"...

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LeetCode 22: Generate Parentheses

Problem Restatement We are given an integer n . We need to generate all combinations of well-formed parentheses using exactly n pairs. For example, if: n = 3 then every result must contain: 3 opening parentheses 3 closing parentheses and the parentheses must be valid. The problem asks for all valid strings, not just the number of valid strings. The constraint is 1 <= n <= 8 . Input and...

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LeetCode 257: Binary Tree Paths

Problem Restatement We are given the root of a binary tree. We need to return all paths from the root to every leaf node. A leaf node is a node with no left child and no right child. Each path must be returned as a string using "->" between node values. For example, this path: 1 \ 2 \ 5 becomes: "1->2->5" The problem asks for all root-to-leaf paths in...

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LeetCode 131: Palindrome Partitioning

Problem Restatement We are given a string s . We need to split it into substrings so that every substring is a palindrome. Return all possible palindrome partitionings of s . A palindrome is a string that reads the same forward and backward, such as: "a" "aa" "aba" "racecar" LeetCode states the task as: partition s so every substring of the partition is a palindrome, then return all possible palindrome...

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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...

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LeetCode 17: Letter Combinations of a Phone Number

Problem Restatement We are given a string digits . Each character is a digit from 2 to 9 . Each digit maps to letters like on a phone keypad: Digit Letters 2 abc 3 def 4 ghi 5 jkl 6 mno 7 pqrs 8 tuv 9 wxyz We need to return all possible letter combinations that the digit string could represent. The answer may be returned in any order. The...

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LeetCode 254: Factor Combinations

Problem Restatement We are given a positive integer n . We need to return all possible ways to write n as a product of factors. Each factor must be between 2 and n - 1 . For example: 8 = 2 * 2 * 2 8 = 2 * 4 So for n = 8 , valid answers are: [[2, 2, 2], [2, 4]] We may return the combinations in...

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LeetCode 79: Word Search

Problem Restatement We are given an m x n grid of characters called board and a string called word . We need to return True if word can be formed by walking through the grid. The walk must follow these rules: Rule Meaning Sequential letters The first visited cell must match word[0] , the next must match word[1] , and so on Adjacent cells only We may move up, down,...

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LeetCode 78: Subsets

Problem Restatement We are given an integer array nums . Every element in nums is unique. We need to return all possible subsets of nums . A subset may contain: Size Meaning 0 elements The empty subset [] Some elements Any valid partial selection All elements The whole array The answer must not contain duplicate subsets. The subsets may be returned in any order. The official problem states that nums...

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LeetCode 351: Android Unlock Patterns

Problem Restatement We have a 3 x 3 Android lock screen. The dots are numbered like this: 1 2 3 4 5 6 7 8 9 Given two integers m and n , count how many valid unlock patterns have length at least m and at most n . A pattern is a sequence of distinct dots. A move from one dot to another is valid if either: The line...

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LeetCode 301: Remove Invalid Parentheses

Problem Restatement We are given a string s containing parentheses and letters. We need to remove the minimum number of invalid parentheses so that the remaining string becomes valid. Return all unique valid strings that can be produced with the minimum number of removals. The answer may be returned in any order. A valid parentheses string means: Every ( has a matching ) . Every ) matches some earlier (...

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LeetCode 77: Combinations

Problem Restatement We are given two integers: n: int k: int We need to return all possible combinations of k numbers chosen from the range: 1, 2, 3, ..., n The order of combinations in the answer does not matter. Inside one combination, order also does not define a new result. For example, [1, 2] and [2, 1] are the same combination. The official constraints are 1 <= n <=...

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LeetCode 52: N-Queens II

Problem Restatement We are given an integer n . We need to count how many ways we can place n queens on an n x n chessboard so that no two queens attack each other. A queen can attack another queen if they are in the same row, same column, or same diagonal. Unlike LeetCode 51, we do not need to return the boards. We only return the number of...

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LeetCode 126: Word Ladder II

Problem Restatement We are given three things: Name Meaning beginWord The word where the transformation starts endWord The word we want to reach wordList The dictionary of valid transformed words We need to return all shortest transformation sequences from beginWord to endWord . A valid transformation sequence looks like this: beginWord -> s1 -> s2 -> ... -> endWord Each step must obey two rules: Adjacent words must differ by...

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LeetCode 51: N-Queens

Problem Restatement We are given an integer n . We need to place n queens on an n x n chessboard so that no two queens attack each other. A queen can attack another queen if they share: The same row The same column The same diagonal Return all distinct valid board configurations. Each board uses "Q" for a queen and "." for an empty square. The answer may be...

#backtracking

LeetCode 3669 - Balanced K-Factor Decomposition

LeetCode 3799 - Word Squares II

LeetCode 3646 - Next Special Palindrome Number

LeetCode 3437 - Permutations III

LeetCode 3376 - Minimum Time to Break Locks I

LeetCode 2014 - Longest Subsequence Repeated k Times

LeetCode 2397 - Maximum Rows Covered by Columns

LeetCode 2698 - Find the Punishment Number of an Integer

LeetCode 2708 - Maximum Strength of a Group

LeetCode 2992 - Number of Self-Divisible Permutations

LeetCode 2597 - The Number of Beautiful Subsets

LeetCode 2212 - Maximum Points in an Archery Competition

LeetCode 3211 - Generate Binary Strings Without Adjacent Zeros

LeetCode 2151 - Maximum Good People Based on Statements

LeetCode 2152 - Minimum Number of Lines to Cover Points

LeetCode 2305 - Fair Distribution of Cookies

LeetCode 1863 - Sum of All Subset XOR Totals

LeetCode 2850 - Minimum Moves to Spread Stones Over Grid

LeetCode 2375 - Construct Smallest Number From DI String

LeetCode 1986 - Minimum Number of Work Sessions to Finish the Tasks

LeetCode 2065 - Maximum Path Quality of a Graph

LeetCode 2664 - The Knight’s Tour

LeetCode 2048 - Next Greater Numerically Balanced Number

LeetCode 3348 - Smallest Divisible Digit Product II

LeetCode 1849 - Splitting a String Into Descending Consecutive Values

LeetCode 2056 - Number of Valid Move Combinations On Chessboard

LeetCode 2044 - Count Number of Maximum Bitwise-OR Subsets

LeetCode 2178 - Maximum Split of Positive Even Integers

LeetCode 1947 - Maximum Compatibility Score Sum

LeetCode 2767 - Partition String Into Minimum Beautiful Substrings

LeetCode 1980 - Find Unique Binary String

LeetCode 473 - Matchsticks to Square

LeetCode 95 - Unique Binary Search Trees II

LeetCode 37 - Sudoku Solver

LeetCode 638 - Shopping Offers

LeetCode 1258 - Synonymous Sentences

LeetCode 254 - Factor Combinations

LeetCode 51 - N-Queens

LeetCode 301 - Remove Invalid Parentheses

LeetCode 465 - Optimal Account Balancing

LeetCode 93 - Restore IP Addresses

LeetCode 679 - 24 Game

LeetCode 131 - Palindrome Partitioning

LeetCode 1239 - Maximum Length of a Concatenated String with Unique Characters

LeetCode 2002 - Maximum Product of the Length of Two Palindromic Subsequences

LeetCode 411 - Minimum Unique Word Abbreviation

LeetCode 90 - Subsets II

LeetCode 425 - Word Squares

LeetCode 79 - Word Search

LeetCode 491 - Non-decreasing Subsequences

LeetCode 140 - Word Break II

LeetCode 1593 - Split a String Into the Max Number of Unique Substrings

LeetCode 526 - Beautiful Arrangement

LeetCode 489 - Robot Room Cleaner

LeetCode 294 - Flip Game II

LeetCode 1774 - Closest Dessert Cost

LeetCode 698 - Partition to K Equal Sum Subsets

LeetCode 996 - Number of Squareful Arrays

LeetCode 357 - Count Numbers with Unique Digits

LeetCode 1655 - Distribute Repeating Integers

LeetCode 78 - Subsets

LeetCode 980 - Unique Paths III

LeetCode 949 - Largest Time for Given Digits

LeetCode 257 - Binary Tree Paths

LeetCode 1096 - Brace Expansion II

LeetCode 22 - Generate Parentheses

LeetCode 40 - Combination Sum II

LeetCode 46 - Permutations

LeetCode 842 - Split Array into Fibonacci Sequence

LeetCode 1467 - Probability of a Two Boxes Having The Same Number of Distinct Balls

LeetCode 1238 - Circular Permutation in Binary Representation

LeetCode 1079 - Letter Tile Possibilities

LeetCode 494 - Target Sum

LeetCode 1799 - Maximize Score After N Operations

LeetCode 784 - Letter Case Permutation

LeetCode 17 - Letter Combinations of a Phone Number

LeetCode 1219 - Path with Maximum Gold

LeetCode 1088 - Confusing Number II

LeetCode 401 - Binary Watch