题目描述：

https://leetcode.com/problems/longest-palindromic-substring/

解决方法：

https://leetcode.com/problems/longest-palindromic-substring/solution/

mycode(c++):

class Solution {
public:
    string longestPalindrome(string s) {
        if( s.length()<1)
            return "";
        int start = 0,end = 0;
        for (int i = 0 ; i < s.length() ; i++){
            int len1 = expandPalindrome(s,i,i);
            int len2 = expandPalindrome(s,i,i+1);
            int len = max(len1,len2);
            if(len>end - start){
                start = i - (len-1)/2;
                end = i + len / 2;
            }
        }
        return s.substr(start,end-start+1);
    }

private:
    int expandPalindrome(string s,int left,int right){
        int l = left;
        int r = right;
        while( l >= 0 && r < s.length() && s.at(l)== s.at(r)){
            l--;
            r++;
        }
        return r - l - 1;
    }
};

心得：主要是回文串的判断问题