1     public String longestPalindrome(String s) {
 2         if (s == null || s.length() <=1)
 3             return s;
 4         
 5         int start = 0;
 6         int longest = 0;
 7         for (int i = 0; i < s.length();){
 8             int p1 = i;
 9             int p2 = i;
10             while(p2<s.length()-1 && s.charAt(p2) == s.charAt(p2+1)){
11                 p2 ++;
12             }
13             i = p2 + 1;
14             while(p1>0 && p2<s.length()-1 && s.charAt(p1-1) == s.charAt(p2+1)){
15                p1--;
16                p2++;
17             }
18             int len = p2 - p1 + 1;
19             if (len > longest){
20                 start = p1;
21                 longest = len;
22             }
23         }
24         return s.substring(start, start + longest);
25     }