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Reverse a given string.
Easy
Frequently Asked
Find indices of two numbers in an array that add up to a specific target.
Easy
Frequently Asked
Check if a string containing just the characters '(', ')', '{', '}', '[' and ']' is valid.
Easy
Frequently Asked
Check if a given string is a palindrome.
Easy
Frequently Asked
Implement the FizzBuzz algorithm.
Easy
Occasionally Asked
Reverse the digits of an integer.
Easy
Occasionally Asked
Merge two sorted linked lists and return it as a new sorted list.
Easy
Occasionally Asked
Remove duplicates from a sorted array in-place and return the new length.
Easy
Occasionally Asked
Convert a Roman numeral to an integer.
Easy
Rarely Asked
Find the longest common prefix string amongst an array of strings.
Easy
Rarely Asked
Determine if a 9x9 Sudoku board is valid.
Medium
Frequently Asked
Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
Hard
Rarely Asked
Merge k sorted linked lists and return it as one sorted list.
Hard
Frequently Asked
Given an input string (s) and a pattern (p), implement regular expression matching with support for '.' and '*' where: '.' Matches any single character. '*' Matches zero or more of the preceding element.
Hard
Frequently Asked
You are given a string s and an array of strings words. You must find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once, in any order, and without any intervening characters.
Hard
Occasionally Asked
Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
Medium
Rarely Asked
Given a string s, find the length of the longest substring without repeating characters.
Medium
Occasionally Asked
Given a binary tree, return the inorder traversal of its nodes' values iteratively.
Medium
Rarely Asked
Given an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].
Medium
Rarely Asked
Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the histogram.
Hard
Rarely Asked