Submission #7761434

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Source Code Expand

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

using i64 = int64_t;

struct Edge{
    int from, to;
};

struct Node{
    int num;
    set<int> visited;
};

using Graph = vector<vector<Edge>>;

int main(){
    int n, m;
    cin >> n >> m;
    Graph graph(n+1, vector<Edge>());
    for(int i=0;i<m;++i){
        int a, b;
        cin >> a >> b;
        graph[a].push_back({a, b});
    }

    set<int> ans;
    for(int i=1;i<=n;++i){
        queue<Node> que;
        for(auto e: graph[i]){
            que.push({e.to, set<int>({e.to})});
        }
        while(!que.empty()){
            auto cur = que.front(); que.pop();
            if(cur.num == i){
                if(ans.size() == 0 || cur.visited.size() < ans.size()){
                    ans = cur.visited;
                }
                break;
            }
            for(auto e: graph[cur.num]){
                if(cur.visited.count(e.to))continue;
                auto st = cur.visited;
                st.insert(e.to);
                que.push({e.to, st});
            }
        }
    }

    if(ans.size() == 0)cout << -1 << endl;
    else{
        cout << ans.size() << endl;
        for(auto e: ans){
            cout << e << endl;
        }
    }

    return 0;
}

Submission Info

Judge Result