Longest Palindromic Substring

var longestPalindrome = function(s) {
    if (s.length == 0) {
        return s;
    }

    var n = s.length;
    var longest = s[0];

    for (var i = 0; i < n; i++) {
        var p1 = expandAroundCenter(s, i, i);
        if (p1.length > longest.length) {
            longest = p1;
        }

        var p2 = expandAroundCenter(s, i, i + 1);
        if (p2.length > longest.length) {
            longest = p2;
        }
    }

    return longest;
};

var expandAroundCenter = function(s, c1, c2) {
    var l = c1,
        r = c2,
        n = s.length;

    while (l > -1 && r < n && s[l] == s[r]) {
        l--;
        r++;
    }

    return s.substr(l + 1, r - l - 1);
};