class Solution {
    public String longestPalindrome(String s) {
        if(s.length() == 0)
            return "";
        char[] c = s.toCharArray();
        int[] range = new int[2];
        for(int i = 0; i < s.length(); i ++){
            i = next(c,i,range);
        }
        return s.substring(range[0],range[1]+1);
    }

    int next(char[] c, int low, int[] range){
        int max = c.length - 1;
        int high = low;
        while(high < max && c[high+1] == c[low])
            high ++;
        int result = high;
        while(low > 0 && high < max && c[high+1] == c[low-1]){
            low --;
            high ++;
        }
        if((high - low) > (range[1]-range[0])){
            range[0] = low; range[1] = high;
        }
        return result;    
    }


}