Longest Palindrome

class Solution {
    fun longestPalindrome(s: String): String {
        if (s.length < 1){
            return "";
        }
        var start = 0;
        var end = 0;
        for (i in 0..s.length - 1){
            val len1 = expandAroundCenter(s, i, i);
            val len2 = expandAroundCenter(s, i, i+1);
            val len = Math.max(len1, len2);
            if (len > (end - start)){
                start = i - (len - 1)/2;
                end = i + len / 2;
            }
        }
        return s.substring(start, end + 1);
    }

    fun expandAroundCenter(s: String, left: Int, right: Int): Int {
        var L = left;
        var R = right;
        while (L >= 0 && R < s.length && s[L] == s[R]){
            L--;
            R++;
        }

        return R-L -1;
    }
}