【leetcode】Longest Palindromic Substring

string longestPalindrome(string s) {
	if(s.size() <= 1)
		return s;
	//vector<vector<bool> >dp(s.size(),vector<bool>(s.size(), false));
	bool dp[1000][1000] = {false};
	//bool **dp = new bool[s.size()][s.size()];
	int Len = s.size();
	int longest = 0;
	int start = 0;
	//init dp[i,i] = true
	for (int i = 0; i < Len; ++i)
		dp[i][i]  = true;
	//init dp[i, i + 1]
 	for (int i = 0; i < Len - 1; ++i)
 		if(s[i] == s[i + 1]) 
 			{
				dp[i][i + 1] = true;
 				longest = 2;
				start = i;
			}
	for (int i = Len - 3; i >= 0; --i)
		for(int j = i + 2; j < Len; ++j)
		{
			if(dp[i + 1][j - 1] && s[i] == s[j])
			{
				dp[i][j] = true;
				if(longest < j - i + 1)
				{
					longest = j - i + 1;
					start = i;
				}
			}
		}
	return s.substr(start,longest);
}