Longest Palindromic Substring 最长回文子串
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.
普通做法，动态规划O(N^2)是能直接出结果的，长度从小到大排列，可以边动规边记录最大值。
Shortest Palindrome 最短回文生成
Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation.
For example:
Given "aacecaaa", return "aaacecaaa".
Given "abcd", return "dcbabcd".
普通做法，即找到从头开始的最长的回文，复杂度为O(N^2)；然后补齐。
事实上，找到以某个点为中心的最长回文子串的经典算法是 Manacher算法，复杂度为O(N)，可求出以字符串中各个点为中心的子串。Manacher算法可参考http://blog.csdn.net/ggggiqnypgjg/article/details/6645824/