func_code_string: #include  bits/stdc++.h    using namespace std;      #define ffor(n) for(int i = 0; i < n; i++)   #define fffor(n) for(int j = 0; j < n; j++)   #define uwu ios_base::sync_with_stdio(false);cin.tie(NULL);   #pragma GCC optimize( Ofast )      const int INF = 1e9 + 7;   const long long INF2 = 1e15;      void solve(void) {       }      bool valid = true;      void verify(int current, vector <vector <int>>& asd, vector <int>& state, vector <int>& res) {    if (valid == false) return;    if (state[current] == 1) {     valid = false;     return;    }    if (state[current] == 2) return;    if (state[current] == 0) {     state[current] = 1;     for (int nextnode: asd[current]) {      verify(nextnode, asd, state, res);     }     state[current] = 2;     res.push_back(current);    }   }         int main(void) {    uwu       int n, k;    cin >> n >> k;    vector <int> v(n);    ffor(n) cin >> v[i];    vector <pair <int, int>> v2(k);    ffor(k) cin >> v2[i].first >> v2[i].second;       set <pair <int, int>> edges;    ffor(n) {     if (v[i] != 0) edges.insert({v[i] - 1, i});    }    ffor(k) {     edges.insert({v2[i].first - 1, v2[i].second - 1});    }        // next in chain    vector <int> next(n, -1), prev(n, -1);    for(int i = 0; i < k; i++) {     next[v2[i].first - 1] = v2[i].second - 1;     prev[v2[i].second - 1] = v2[i].first - 1;    }    vector <int> chained(n, -1);     for(int i = 0; i < n; i++) {     if (chained[i] != -1) continue;     auto head = i, tail = i;     chained[i] = i;     while(prev[head] != -1) {      if (chained[prev[head]] != -1) {       valid = false;       break;      }      head = prev[head];      chained[head] = i;     }     while(next[tail] != -1) {      if (chained[next[tail]] != -1) {       valid = false;       break;      }      tail = next[tail];      chained[tail] = i;     }     while(tail != head) {      if (v[tail] != 0 && chained[v[tail] - 1] != i) {       edges.insert({v[tail] - 1, head});      }      tail = prev[tail];     }    }        // adjacency list    vector <vector <int>> asd(n);    for(auto e: edges) {     asd[e.first].push_back(e.second);    }        // topological sort    vector <int> state(n), res;    for(int i = 0; i < n; i++) {     if (v[i] == 0) {      verify(i, asd, state, res);     }    }        vector <bool> visited(n);    reverse(res.begin(), res.end()); // reverse reversed topological sort    vector <int> ans, order_of(n);            for(int e: res) {     auto current = e;     if (visited[current]) continue;     // follow chain     while(next[current] != -1 && visited[next[current]] != true) {      ans.push_back(current);      visited[current] = true;      current = next[current];     }     ans.push_back(current);     visited[current] = true;     current = next[current];    }         if (valid) {     // find position in answer     for(int i = 0; i < ans.size(); i++) {      order_of[ans[i]] = i;     }     // verify ordering     for(int i = 0; i < v.size(); i++) {      if (v[i] == 0) continue;      if (order_of[v[i] - 1] > order_of[i]) valid = false;     }     for(int i = 0; i < k; i++) {      if (order_of[v2[i].first - 1] + 1 != order_of[v2[i].second - 1]) valid = false;     }     if (valid) {      for (auto e: ans) cout << e + 1 <<    ;      cout <<   n ;     }     else cout << 0 <<   n ;    }    else cout << 0 <<   n ;   }                         /*   C: Users User Desktop comp_programming final_straw_after_this_im_switching_to_vs_code finally_switched_to_geany.cpp   */   