为什么会TLE呀！大佬快教教蒟蒻！

#include <iostream>
using namespace std;

int n, m; bool a[1010][1010], vis[1010];
int dfs(int x) {
    int ans = x;
    for (int i = 1; i <= n; i++) {
        if (a[x][i] && !vis[i]) {
            vis[i] = true;
            ans = max(dfs(i), ans);
            vis[i] = false;
        }
    }
    return ans;
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y; cin >> x >> y;
        a[x][y] = true;
    }
    for (int i = 1; i <= n; i++)
        cout << dfs(i) << " ";
    return 0;
}