class Solution {
    public String longestPalindrome(String s) {
        if (s==null || s.length() < 1) return "";
        int start = 0,end = 0;
        for(int i =0;i<s.length();i++){
            int l1 = check(s,i,i);
            int l2 = check(s,i,i+1);
            int l = Math.max(l1,l2);
            if(l>end- start){
                start = i-((l-1)/2);
                end = i + (l/2);
            }
        }
        return s.substring(start,end+1);
    }
    public int check (String s,int left ,int right){
        if (left>right) return 0;

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

        return right-left-1;
    }
}