最长回文子串——区间dp

class Solution {
public:
    string longestPalindrome(string s) {
        int n = s.size();
        vector<vector<int>> dp(n + 1, vector<int>(n + 1, 0));

        // dp[i][j] = dp[i + 1][j - 1]

        string ans = "";
        int idx = 0;
        int m = 0;
        for (int i = n - 1; i >= 0; i--) {
            for (int j = i; j < n; j++) {
                if (s[i] == s[j]) {
                    if (i + 1 > j - 1) dp[i][j] = 1;
                    else dp[i][j] = dp[i + 1][j - 1];
                }
                if (dp[i][j] && m < j - i + 1) {
                    m = j - i + 1;
                    idx = i;
                }
            }
        }

        for (int i = idx; i <= idx + m - 1; i++) ans += s[i];
        return ans;
    }
};