摘要：
Given a string containing just the characters'(', ')', '{', '}', '[' and ']', determine if the input string is valid. The brackets must close in the c 阅读全文
摘要：
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. "A man, a plan, a canal: Panama" is a pa 阅读全文
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Follow up for "Unique Paths": Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space 阅读全文
摘要：
A robot is located at the top-left corner of a m x ngrid (marked 'Start' in the diagram below). The robot can only move either down or right at any po 阅读全文