class Solution {
    private String maxStr;
    public String longestPalindrome(String s) {
	if (s.length() < 2){
            return s;
        }
        maxStr = s.substring(0,1);
        for(int i = 0; i < s.length()-1; i++){
            extendPalindrome(s, i, i);
            extendPalindrome(s, i, i+1);
        }
        return maxStr;
    }
    private void extendPalindrome(String s, int begin, int end){
        while(begin>=0 && end < s.length() && s.charAt(begin) == s.charAt(end)){
            begin -= 1;
            end += 1;
        }
        if(maxStr.length() < end-begin){
            maxStr = s.substring(begin+1, end);
        }
    }
}