Medium LeetCode problems

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…

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…

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…

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.

Generate Parentheses

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

Swap Nodes in Pairs

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

Divide Two Integers

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

Next Permutation

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

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.

Valid Sudoku

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

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…

Multiply Strings

Multiply Strings requires simulating integer multiplication using only string operations without direct numeric conversi…