记忆化搜索

#include <bits/stdc++.h>
using namespace std;

const int N = 510;

vector<int> v[N];
bool vis[N];
int num[N];
int n, m, s, d;

int dfs(int x)
{
    vis[x] = true;
    if (num[x]) return num[x];
    int res = 0;
    for (auto c : v[x]) res += dfs(c);
    return num[x] = res;
}

int main()
{
    cin >> n >> m;
    while (m--)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        v[a].push_back(b);
    }
    cin >> s >> d;

    num[d] = 1;
    cout << dfs(s) << ' ';
    bool f = true;
    for (int i = 1; i <= n; i++)
        if (!num[i] && vis[i]) f = false;

    cout << (f ? "Yes" : "No");

    return 0;
}