5. Longest Palindromic Substring

class Solution {
public:
   string longestPalindrome(string s) {
    int len = s.length();
    int max_l = 0;//最长回文子串长度
    int max_s = 0;//最长回文子串开头的位置
    int cur_len;
    int cur_s;
    for (int i = 0; i < len; i++) {//字符串的长度是奇数
        for (int j = 0; i + j<len&&i - j>-1; j++) {
            if (s[i + j] != s[i - j]) {
                break;
            }
            cur_len = j * 2 + 1;
            cur_s = i - j;
        }
        if (cur_len > max_l) {
            max_s = cur_s;
            max_l = cur_len;
        }
        for (int j = 0; i - j > -1 && i + j + 1 < len; j++) {//字符串为偶数长度
            if (s[i + j + 1] != s[i - j]) {
                break;
            }
            cur_len = 2 * j + 2;
            cur_s = i - j;
        }
        if (cur_len > max_l) {
            max_s = cur_s;
            max_l = cur_len;
        }
    }
    return s.substr(max_s, max_l);
}
};