牛客 Sequence Game 学校OJ测出来20分

求各位大佬帮调

#include <bits/stdc++.h>
using namespace std;
const int N = 5e3 + 5, M = 1e3 + 5;
int n, k;
int a, flag[N][M], dp[N][M];
int ans = 0;
int main() {
	cin >> k >> n;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= k; j++) {
			cin >> a;
			flag[i][a] = 1;
		}
	}
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= 1e3; j++) {
			dp[i][j]=dp[i-1][j];
			dp[i][j] = max(max(dp[i][j - 1], dp[i][j]), dp[i - 1][j - 1] + flag[i][j]);
			ans = max(ans, dp[i][j]);
		}
	}
	cout << ans;
	return 0;
}