Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
Example:
Input: "babad" Output: "bab" Note: "aba" is also a valid answer.
Example:
Input: "cbbd" Output: "bb"
把题目放着，先想想^^
5、最长回文子串Longest Palindromic Substring
原文：http://www.cnblogs.com/hozhangel/p/7739645.html