Leet code problem 5 Longest Palindromic Substring

class Solution {
public:
    string longestPalindrome(string s) {
        int x = -1;
        int l = -1;
        for (int i = 0; i < (int)s.size(); ++i){
            int left = i;
            int right = i;
            while (left >= 0 && right < s.size() && s[left] == s[right]){
                --left;
                ++right;
            }
            int tl = right - left - 1;
            if (tl > l){
                l = tl;
                x = left+1;
            }
            left = i-1;
            right = i;
            while (left >= 0 && right < s.size() && s[left] == s[right]){
                --left;
                ++right;
            }
            tl = right - left - 1;
            if (tl > l){
                l = tl;
                x = left+1;
            }

        }
        if (l > -1){
            return s.substr(x, l);
        }
        return "";
    }
}; 

号称还有O(n)的算法：

http://articles.leetcode.com/longest-palindromic-substring-part-ii/

后面再研究，