【字符串】最长回文子串Longest Palindromic Substring

题目：给定一个字符串，找到其中的最长的回文子串

回文串：字符串反过来和它本身相同

例如：给定字符串“abcdzdcab”，应返回“cdzdc”；

C++程序如下

    string longestPalindrome(string& s) {        if (s.empty()) return "";        if (s.size() == 1) return s;        int min_start = 0, max_len = 1;        for (int i = 0; i < s.size();) {          if (s.size() - i <= max_len / 2) break;          int j = i, k = i;          while (k < s.size()-1 && s[k+1] == s[k]) ++k; // Skip duplicate characters.          i = k+1;          while (k < s.size()-1 && j > 0 && s[k + 1] == s[j - 1]) { ++k; --j; } // Expand.          int new_len = k - j + 1;          if (new_len > max_len) { min_start = j; max_len = new_len; }        }        return s.substr(min_start, max_len);        // Write your code here    }