[LeetCode #5] 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.

class Solution {
public:
    string longestPalindrome(string s) {
        int n = s.size();
        if (n <= 1) return s;
        
        int start = 0;
        int maxlen = 0;
        bool ispal[1000][1000] = {false};
        
        for (int i = 0; i < n; i++){
            for (int j = i; j >= 0; j--){
                if (s[i] == s[j] && (ispal[j+1][i-1] || j+1 > i-1)){
                    ispal[j][i] = true;
                    if (i - j + 1 > maxlen){
                        maxlen = i - j + 1;
                        start = j;
                    }
                }
            }
        }
        
        return s.substr(start, maxlen);
    }
};