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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.
题目大意：给一个字符串S，存在唯一的最长的回文子串，求这个回文子串。
解题思路：首先这个题有O(n)的解，是在http://articles.leetcode.com/2011/11/longest-palindromic-substring-part-ii.html这里有详细的解释，本文的算法是O(n^2)的，中规中矩的做法。回文有两种，abba和aba，本文分别对子串以i为中心进行检查偶数和奇数哪个长，同时记录长度，下标，奇偶等信息。
Talk is cheap>>
public String longestPalindrome(String s) { if (s == null || s.length() <= 1) { return s; } int max_len = 0, pos = 0; boolean odd = false; for (int i = 0; i < s.length(); i++) { int forward = i - 1; int backward = i + 1; int len = 0; while (forward >= 0 && backward < s.length() && s.charAt(forward) == s.charAt(backward)) { forward--; backward++; len++; } if (max_len < (len * 2 + 1)) { max_len = len * 2 + 1; odd = true; pos = i; } len = 0; forward = i; backward = i + 1; while (forward >= 0 && backward < s.length() && s.charAt(forward) == s.charAt(backward)) { forward--; backward++; len++; } if (max_len < len * 2) { max_len = len * 2; odd = false; pos = i; } } if (odd) { return s.substring(pos - (max_len - 1) / 2, pos + (max_len - 1) / 2 + 1); } return s.substring(pos - max_len / 2 + 1, pos + max_len / 2 + 1); }
Longest Palindromic Substring——LeetCode
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原文地址：http://www.cnblogs.com/aboutblank/p/4401146.html
