LeetCode-求最长回文子序列

题目：给定一个字符串，求它的最长回文子串

/*求最长回文子串,以当前字符为中心，向两边同时拓展*/
string longestPalindrome(string s) 
{
    int len = s.length();
    if(len < 2)
        return s;
    int leftMost = 0, rightMost = 0;
    int i = 0;
    int start, end;
    while(i < len)
    {
        start = i;
        i++;
        while(i < len && s[i] == s[start])  //中间重复的字符满足回文条件
        {
            i++;
        }
        end = i-1;
        while(start-1 >= 0 && end+1 < len && s[start-1] == s[end+1])  //两边同时拓展判断是否相等
        {
            start--;
            end++;
        }
        if(end - start > rightMost - leftMost)  //保存最长的字符区间
        {
            leftMost = start;
            rightMost = end;
        }
    }
    return s.substr(leftMost, rightMost-leftMost+1); // 返回最长回文子串
}