Given a Binary Search Tree and a target number, return true if there exist two elements in the BST such that their sum is equal to the given target. E ...

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. (i.e., [0,0,1,2,2,5,6] might become [2,5,6,0,0,1,2]). Y ...

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. (i.e., [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]). Y ...

Given a string containing just the characters ‘(‘ and ‘)’, find the length of the longest valid (well-formed) parentheses substring. ExampleNo.1Input: ...

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: 1 ...

Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique q ...

Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the thr ...

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the s ...

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 endpoi ...

The count-and-say sequence is the sequence of integers with the first five terms as following: 123451. 12. 113. 214. 12115. 111221 ...