新手訓練系列 ~ 圖論

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

//{
//#pragma gcc optimize("Ofast,unroll-loops")
//#pragma gcc target("sse,sse2,sse3,ssse3,sse4,avx,avx2,fma,abm,mmx,popcnt,tune=native")
//#define int long long
//#define double long double
#define MP make_pair
#define F first
#define S second
#define MOD 1000000007
//}

vector<bool> vis;
vector<vector<int>> edge;

void dfs(int u)
{
    vis[u] = true;
    for (int i : edge[u])
        if (!vis[i])
            dfs(i);
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int n, m;
    while (cin >> n >> m)
    {
        vis.resize(n + 1), edge.resize(n + 1);
        for (int i = 1; i <= n; i++)
            vis[i] = false, edge[i].clear();

        int u, v;
        while (m--)
            cin >> u >> v, edge[u].push_back(v);

        int a, b;
        cin >> a >> b;

        dfs(a);
        if (vis[b])
            cout << "Yes!!!\n";
        else
            cout << "No!!!\n";
    }

    return 0;
}

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