摘要：
题目：Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.For example,"A man, a plan, a canal: P... 阅读全文
摘要：
题目：Given a string containing just the characters'(',')','{','}','['and']', determine if the input string is valid.The brackets must close in the corre... 阅读全文