Longest Palindromic Substring

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

string longestPalindrome(string s) {

	vector<vector<bool> >dp(s.size(), vector<bool>(s.size(), true));
	//bool dp[s.size()][s.size()];
	for (int i = 0; i < s.size(); i++)
	for (int j = 0; j < s.size(); j++)
	if (i >= j)
		dp[i][j] = true;
	else dp[i][j] = false;
	int begin = 0, maxlen = 1;
	for (int len = 1; len < s.size(); ++len){
		for (int idx = 0; idx + len < s.size(); ++idx)
		{
			if (s[idx] == s[idx + len]){
				dp[idx][idx + len] = dp[idx + 1][idx + len - 1];
				if (dp[idx][idx + len] == true && len + 1 > maxlen){
					begin = idx;
					maxlen = len + 1;
				}

			}
			else
				dp[idx][idx + len] = false;
		}
	}
	return s.substr(begin, maxlen);
}

Time Limit Exceeded

 string longestPalindrome(string s) {
        int len = s.length(), max = 1, ss = 0, tt = 0;
        bool flag[len][len];
        for (int i = 0; i < len; i++)
            for (int j = 0; j < len; j++)
                if (i >= j)
                    flag[i][j] = true;
                else flag[i][j] = false;
        for (int j = 1; j < len; j++)
            for (int i = 0; i < j; i++)
            {
                if (s[i] == s[j])
                {
                    flag[i][j] = flag[i+1][j-1];
                    if (flag[i][j] == true && j - i + 1 > max)
                    {
                        max = j - i + 1;
                        ss = i;
                        tt = j;
                    }
                }
                else flag[i][j] = false;
            }
        return s.substr(ss, max);
    }

AC

Longest Palindromic Substring

原文：http://blog.csdn.net/li_chihang/article/details/44655093