Longest Palindromic Substring

Given a stringS, find the longest palindromic substring inS. You may assume that the maximum length ofSis 1000, and there exists one unique longest palindromic substring.

Example

Given the string ="abcdzdcab", return"cdzdc".

public String longestPalindrome(String s) {
    if(s == null || s.length() == 0) {
        return "";
    }
    int n = s.length();
    boolean[][] dp = new boolean[n][n];
    String res = null;
    int max = 0;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n - i; j++) {
            int end = j + i;
            if(s.charAt(end) == s.charAt(j) && (end - j <= 2 || dp[j + 1][end - 1])) {
                dp[j][end] = true;
            }
            if(end - j + 1 > max && dp[j][end]) {
                max = end - j + 1;
                res = s.substring(j, end + 1);
            }
        }
    }
    return res;
}