5.txt

class Solution {
    
private:
    int maxLen;
    int start;
    
public:
    string longestPalindrome(string s)
    {
        int len = s.size();
        if(len < 2 ) return s;
        start = maxLen = 0;
        for(int i = 0; i < len; i++)
        {
            valid(s,i,i);
            valid(s,i,i+1); //假定是奇数；
            
        }
        //cout<<start<<" "<<maxLen<<endl;
        
        return s.substr(start,maxLen);
        
        
        
        
    }
private:
    void valid(string &s, int left, int right )
    {
        while(s[left] == s[right] && left >= 0 && right < s.size())
        {
            left--;
            right++;
            
        }
        if(right-left-1 > maxLen)
        {
        start = left+1;
        maxLen = right-left-1;
            
            
            
        }

    }
};