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.

方法：

Manacher‘s algorithm，具体看这里http://leetcode.com/2011/11/longest-palindromic-substring-part-ii.html

或者有比较好的博客：http://www.felix021.com/blog/read.php?2040

[LeetCode] Longest Palindromic Substring