Longest Palindromic Substring

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.

Java

public class Solution {
    public String longestPalindrome(String s) {
        if(s == null || s.length() == 0) {
            return s;
        }

        int len = s.length(), start = 0, max = 1;
        boolean[][] map = new boolean[len][len];

        for(int i = 0; i < len; i++) {
            map[i][i] = true;
        }
        for(int i = 0; i < len - 1; i++) {
            if(s.charAt(i) == s.charAt(i + 1)) {
                map[i][i + 1] = true;
                start = i;
                max = 2;
            }
        }
        for(int l = 3; l <= len; l++) {
            for(int i = 0; i <= len - l; i++) {
                int j = i + l - 1;
                if(s.charAt(i) == s.charAt(j) && map[i + 1][j - 1]) {
                    map[i][j] = true;
                    start = i;
                    max = l;
                }
            }
        }

        return s.substring(start, start + max);
    }
}