LeetCode 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.

如果一个字符串从左向右写和从右向左写是一样的，这样的字符串就叫做palindromic string，如aba,或者abba。本题是这样的，给定输入一个字符串，要求输出一个子串，使得子串是最长的padromic string。

public class Solution {
    public String longestPalindrome(String s) {
        String longets = "";
        if (s.length() <= 1) {
            return s;
        }
        boolean[][] isP = new boolean[s.length()][s.length()];
        for (int i = 0; i < s.length(); i++) {
            isP[i][i] = true;
        }
        for (int i = 0; i < s.length()-1; i++) {
            if (s.charAt(i) == s.charAt(i + 1)) {
                isP[i][i + 1] = true;
                longets = s.substring(i, i + 2);
            }
        }

        for (int l = 3; l <= s.length(); l++) {
            for (int i = 0; i <= s.length() - l; i++) {
                int j = i + l - 1;
                if (s.charAt(i) == s.charAt(j)) {
                    isP[i][j] = isP[i + 1][j - 1];
                    if (isP[i][j] && l > longets.length()) {
                        longets = s.substring(i, j + 1);
                    }
                }
            }
        }
        return longets;

    }


}