/**
 * @param {string} s
 * @return {string}
 */
var longestPalindrome = function(s) {
    if (s.length < 2) {
        return s;
    }

    let left = 0, right = 0, maxLeft = 0, maxRight = 0;

    for (let index = 0; index < s.length; index++) {
        left = index, right = index;

        while (right < s.length - 1 && s[right] == s[right + 1]) {
            right++;
        }

        while (left > 0 && right < s.length - 1 && s[left - 1] === s[right + 1]) {
            left--;
            right++;
        }

        if (maxRight - maxLeft == s.length - 1)
            return s;
        if (right - left > maxRight - maxLeft) {
            maxLeft = left, maxRight = right;
        }
    }
    return s.substring(maxLeft, maxRight + 1);
};