func_code_string: #include <bits/stdc++.h>   using namespace std;   using ll = long long;   using pii = pair<int, int>;   template <class T>   using V = vector<T>;   template <class T>   using VV = V<V<T>>;   constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }   template <class T, class U>   void chmin(T &t, const U &u) {     if (t > u) t = u;   }   template <class T, class U>   void chmax(T &t, const U &u) {     if (t < u) t = u;   }   template <class T, class U>   ostream &operator<<(ostream &os, const pair<T, U> &p) {     os <<  (  << p.first <<  ,  << p.second <<  ) ;     return os;   }   template <class T>   ostream &operator<<(ostream &os, const vector<T> &v) {     os <<  { ;     for (int i = 0; i < (v.size()); i++) {       if (i) os <<  , ;       os << v[i];     }     os <<  } ;     return os;   }   int main() {     ios::sync_with_stdio(false);     cin.tie(nullptr);     int tc;     cin >> tc;     while (tc--) {       int n, m;       cin >> n >> m;       V<int> ans;       VV<int> g(n);       for (int i = 0; i < (m); i++) {         int a, b;         cin >> a >> b;         --a, --b;         g[a].push_back(b);       }       VV<int> st(n, V<int>(3));       for (int i = 0; i < (n); i++) {         int c;         if (st[i][1]) {           c = 2;         } else if (st[i][0]) {           c = 1;         } else {           c = 0;         }         if (c == 2) ans.push_back(i);         for (int to : g[i]) {           st[to][c] = 1;         }       }       cout << ans.size() <<   n ;       for (auto v : ans) cout << v + 1 <<    ;       cout <<   n ;     }     return 0;   }   