Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is: 1234567[...

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string ...

Given a linked list, remove the nth node from the end of list and return its head. For example,123Given linked list: 1->2->3->4->5, and n = 2.Aft...

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives...

Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone butt...

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You ma...

Given n non-negative integers a1, a2, …, an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of l...

Implement regular expression matching with support for ‘.’ and ‘*’.12345678910111213141516'.' Matches any single character.'*' Matches zero or more of the pr...

Given a string, find the first non-repeating character in it and return it’s index. If it doesn’t exist, return -1. Examples:12345s = "leetcode"return 0.s = ...

Given an arbitrary ransom note string and another string containing letters from all the magazines, write a function that will return true if the ransom note...