题目:
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 longest palindromic substring.
链接：https://leetcode.com/problems/longest-palindromic-substring/
题解：
Reference:
5. Longest Palindromic Substring
原文：http://www.cnblogs.com/yrbbest/p/4430093.html