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。

 1 public class Solution {
 2     public String longestPalindrome(String s) {
 3         String longets = "";
 4         if (s.length() <= 1) {
 5             return s;
 6         }
 7         boolean[][] isP = new boolean[s.length()][s.length()];
 8         for (int i = 0; i < s.length(); i++) {
 9             isP[i][i] = true;
10         }
11         for (int i = 0; i < s.length()-1; i++) {
12             if (s.charAt(i) == s.charAt(i + 1)) {
13                 isP[i][i + 1] = true;
14                 longets = s.substring(i, i + 2);
15             }
16         }
17 
18         for (int l = 3; l <= s.length(); l++) {
19             for (int i = 0; i <= s.length() - l; i++) {
20                 int j = i + l - 1;
21                 if (s.charAt(i) == s.charAt(j)) {
22                     isP[i][j] = isP[i + 1][j - 1];
23                     if (isP[i][j] && l > longets.length()) {
24                         longets = s.substring(i, j + 1);
25                     }
26                 }
27             }
28         }
29         return longets;
30 
31     }
32 
33 
34 }