字符串系列一＞最长回文子串

class Solution {
    public String longestPalindrome(String s) {
        char[] ss = s.toCharArray();
        int n = ss.length;
        int begin = 0;//返回结果的起始字符串
        int len = 0;//判断返回的字符串是否为最长的字符串
        for(int i = 0; i < n; i++){
            //先扩展偶数
            int left = i, right = i;
            while(right < n && left >= 0 && ss[left] == ss[right]){
                left--;
                right++;
            }
            if(right-left-1 > len){
                len = right-left-1;
                begin = left+1;
            }

            //扩展偶数
            left = i;
            right = left+1;
            while(right < n && left >= 0 && ss[left] == ss[right]){
                left--;
                right++;
            }
            if(right-left-1 > len){
                len = right-left-1;
                begin = left+1;
            }
        }

        return s.substring(begin,begin + len);
    }
}