LeetCode Problem Bank

Two Sum

Two Sum is solved fastest by storing seen values in a hash map and checking each number's needed complement once.

Add Two Numbers

Add Two Numbers requires careful linked-list pointer manipulation to sum digits while handling carries efficiently in in…

Longest Substring Without Repeating Characters

Find the length of the longest substring without repeating characters using a sliding window and hash map to track state…

Median of Two Sorted Arrays

Find the median of two sorted arrays using binary search for efficient O(log(min(m, n))) time complexity.

Longest Palindromic Substring

Find the longest contiguous palindromic substring in a given string using dynamic programming and two-pointer expansion …

Zigzag Conversion

Convert a string into a zigzag pattern across multiple rows and read it line by line efficiently for string manipulation…

Reverse Integer

Reverse Integer challenges you to invert the digits of a signed 32-bit integer, handling overflow and negative values ca…

String to Integer (atoi)

Convert a string to a 32-bit signed integer by carefully parsing characters, handling signs, and ignoring invalid traili…

Palindrome Number

Determine if a given integer reads the same forward and backward using a math-driven solution strategy without convertin…

Regular Expression Matching

The Regular Expression Matching problem involves checking if a string matches a pattern using '.' and '*'.

Container With Most Water

Find two vertical lines that can form a container with the most water in a given array of heights.

Integer to Roman

Convert a given integer to its Roman numeral representation using hash table mapping and decimal place math operations e…

Roman to Integer

Convert a Roman numeral string into an integer using a hash table and mathematical principles to determine value order.

Longest Common Prefix

Find the longest common prefix in an array of strings, returning an empty string if none exists.

3Sum

Given an integer array, return all unique triplets where the sum is zero using two-pointer scanning with careful duplica…

3Sum Closest

Find the sum of three integers in an array that is closest to a given target using two-pointer scanning.

Letter Combinations of a Phone Number

Generate all letter combinations a digit string can represent using backtracking with pruning, leveraging hash table map…

4Sum

The 4Sum problem requires finding all unique quadruplets in an array that sum to a specific target value.

Remove Nth Node From End of List

Remove the nth node from the end of a linked list using a two-pointer approach to solve efficiently.

Valid Parentheses

Determine if a string of parentheses, brackets, and braces is correctly nested using a stack for proper order validation…

Merge Two Sorted Lists

Merge two sorted linked lists by splicing nodes into one sorted list using linked-list pointer manipulation and recursio…

Generate Parentheses

Generate Parentheses requires generating all valid combinations of parentheses with given pairs using backtracking and s…

Merge k Sorted Lists

Merge k Sorted Lists requires efficiently combining multiple sorted linked lists into one using pointers and priority qu…

Swap Nodes in Pairs

Learn how to swap every adjacent linked-list pair by rewiring nodes safely without changing values or breaking the remai…

Reverse Nodes in k-Group

Reverse Nodes in k-Group challenges you to reverse segments of a linked list in groups of size k.

Remove Duplicates from Sorted Array

Learn how to remove duplicates from a sorted array in-place using two-pointer scanning while preserving element order.

Remove Element

Remove Element challenges you to remove a value from an array in-place using efficient two-pointer scanning and tracking…

Find the Index of the First Occurrence in a String

Locate the first occurrence of a substring within a string using a two-pointer scanning strategy and invariant tracking …

Divide Two Integers

Solve Divide Two Integers by turning repeated subtraction into bit-shifted chunk subtraction with careful sign and overf…

Substring with Concatenation of All Words

Find all starting indices of substrings in a string that are concatenations of a given list of words.

Next Permutation

Next Permutation is a medium-difficulty problem focusing on generating the next lexicographically greater permutation of…

Longest Valid Parentheses

Compute the length of the longest well-formed parentheses substring using state transition dynamic programming and stack…

Search in Rotated Sorted Array

Find the index of a target in a rotated sorted array using a careful binary search that handles pivot shifts.

Find First and Last Position of Element in Sorted Array

Locate the first and last index of a target in a sorted array using binary search for precise O(log n) performance.

Search Insert Position

Find the correct index for a target value in a sorted array using binary search, or return the position where it should …

Valid Sudoku

Check if a 9x9 Sudoku board is valid by scanning rows, columns, and sub-boxes with hash lookups, ensuring no duplicates …

Sudoku Solver

Solve the Sudoku puzzle by filling empty cells while respecting Sudoku's rules using array scanning and backtracking.

Count and Say

Count and Say requires building the nth sequence term by iteratively applying a run-length encoding on strings of digits…

Combination Sum

Find all unique combinations of numbers from a distinct array that sum to a target using controlled backtracking search.

Combination Sum II

Find all unique combinations of numbers that sum to a target using backtracking with careful pruning to avoid duplicates…