摘要： 441. Arranging Coins You have a total of n coins that you want to form in a staircase shape, where every k-th row must have exactly k coins. Given n, 阅读全文

摘要： 20. Valid Parentheses Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. The brack 阅读全文

摘要： 1. Two Sum Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input wo 阅读全文