Longest Palindromic Substring

 1 var longestPalindrome = function(s) {
 2     if (s.length == 0) {
 3         return s;
 4     }
 5 
 6     var n = s.length;
 7     var longest = s[0];
 8 
 9     for (var i = 0; i < n; i++) {
10         var p1 = expandAroundCenter(s, i, i);
11         if (p1.length > longest.length) {
12             longest = p1;
13         }
14 
15         var p2 = expandAroundCenter(s, i, i + 1);
16         if (p2.length > longest.length) {
17             longest = p2;
18         }
19     }
20 
21     return longest;
22 };
23 
24 var expandAroundCenter = function(s, c1, c2) {
25     var l = c1,
26         r = c2,
27         n = s.length;
28 
29     while (l > -1 && r < n && s[l] == s[r]) {
30         l--;
31         r++;
32     }
33 
34     return s.substr(l + 1, r - l - 1);
35 };