5. Longest Palindromic Substring java solutions

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.

public class Solution {
    public String longestPalindrome(String s) {
        if(s == null || s.length() <= 1) return s;
        String ans = s.substring(0,1);
        for(int i = 0; i < s.length(); i++){
            String tmp = findPalindrome(s,i,i);//回文为奇数的情况
            if(tmp.length() > ans.length()) ans = tmp;
            
            tmp = findPalindrome(s,i,i+1);// 回文为偶数的情况
            if(tmp.length() > ans.length()) ans = tmp;
        }
        return ans;
    }
    
    public String findPalindrome(String str, int s, int e){
        while(s >=0 && e < str.length() && str.charAt(s) == str.charAt(e)){
            s--; e++;
        }
        return str.substring(++s,e);
    }
}

时间复杂度O(N*(N+N+1))

本题也可以使用DP做法：

参考DP:http://blog.csdn.net/soszou/article/details/37312317