摘要：
问题：Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique lon... 阅读全文
摘要：
问题：Given a digit string, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telep... 阅读全文
摘要：
问题:Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.The brackets must close in th... 阅读全文