Online Course in BSU - 770C - Codeforces

#include <bits/stdc++.h>

using namespace std;

const int BIG_N=100001;

deque<int> ans,ret;

vector<vector<int>> adj(BIG_N);

bool dfs(vector<bool>& look,vector<int>& vu,int node){

if (adj[node].empty()) return true;

for (auto& i:adj[node]){

if (vu[i] <= 1){

ans.emplace_back(i);

vu[i]++;

if (dfs(look,vu,i)) return true;

}

else if (look[i]) return true;

else return false;

}

return false;

}

int main(){

ios::sync_with_stdio(false);

cin.tie(nullptr);

int n,k;

cin >> n >> k;

vector<int> v(k);

for (int i=0; i<k; ++i) cin >> v[i];

for (int i=1; i<=n; ++i){

int t;

cin >> t;

for (int j=0; j<t; ++j){

int a;

cin >> a;

adj[i].emplace_back(a);

}

}

vector<int> vu(n+1);

vector<bool> look(n+1);

for (auto& i:v){

bool ok=true;

if (!vu[i]){

ok=dfs(look,vu,i);

ans.emplace_back(i);

}

if (!ok){

cout << -1;

return 0;

}

else{

for (auto& i:ans) look[i]=true;

reverse(ans.begin(),ans.end());

for (auto& i:ans) ret.emplace_back(i);

ans.clear();

}

}

cout << ret.size() << '\n';

for (auto& i:ret) cout << i << ' ';

return 0;

}