func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename T>   ostream &operator<<(ostream &os, const vector<T> &v) {     os <<  { ;     string sep;     for (const auto &x : v) os << sep << x, sep =  ,  ;     return os <<  } ;   }   template <typename T, size_t size>   ostream &operator<<(ostream &os, const array<T, size> &arr) {     os <<  { ;     string sep;     for (const auto &x : arr) os << sep << x, sep =  ,  ;     return os <<  } ;   }   template <typename A, typename B>   ostream &operator<<(ostream &os, const pair<A, B> &p) {     return os <<  (  << p.first <<  ,   << p.second <<  ) ;   }   void dbg_out() { cerr << endl; }   template <typename Head, typename... Tail>   void dbg_out(Head H, Tail... T) {     cerr <<     << H;     dbg_out(T...);   }   auto random_address = [] {     char *p = new char;     delete p;     return (uint64_t)p;   };   mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count() *                  (random_address() | 1));   template <typename T>   void output_vector(const vector<T> &v, bool add_one = false, int start = -1,                      int end = -1) {     if (start < 0) start = 0;     if (end < 0) end = int(v.size());     for (int i = start; i < end; i++)       cout << v[i] + (add_one ? 1 : 0) << (i < end - 1 ?     :   n );   }   const int ATTEMPTS = 50;   int N, M;   vector<vector<int>> adj;   vector<int> tour_index;   vector<array<int, 2>> low_link;   vector<bool> in_stack;   int tour;   vector<int> tour_list;   array<int, 2> combine(array<int, 2> x, int y) {     array<int, 3> a = {x[0], x[1], y};     sort(a.begin(), a.end());     return {a[0], a[1]};   }   array<int, 2> combine(array<int, 2> x, array<int, 2> y) {     array<int, 4> a = {x[0], x[1], y[0], y[1]};     sort(a.begin(), a.end());     return {a[0], a[1]};   }   bool interesting_dfs(int node) {     tour_index[node] = tour++;     tour_list.push_back(node);     low_link[node] = {tour_index[node], tour_index[node]};     in_stack[node] = true;     for (int neighbor : adj[node])       if (tour_index[neighbor] < 0) {         if (!interesting_dfs(neighbor)) return false;         low_link[node] = combine(low_link[node], low_link[neighbor]);       } else if (in_stack[neighbor]) {         low_link[node] = combine(low_link[node], tour_index[neighbor]);       } else {         return false;       }     in_stack[node] = false;     return true;   }   vector<int> save_interesting;   bool check_interesting(int node) {     if (save_interesting[node] >= 0) return save_interesting[node];     tour_index.assign(N, -1);     low_link.resize(N);     in_stack.assign(N, false);     tour = 0;     tour_list.clear();     return (save_interesting[node] = interesting_dfs(node));   }   void run_case() {     cin >> N >> M;     adj.assign(N, {});     for (int i = 0; i < M; i++) {       int u, v;       cin >> u >> v;       u--;       v--;       adj[u].push_back(v);     }     save_interesting.assign(N, -1);     int root = -1;     for (int iter = 0; iter < ATTEMPTS; iter++) {       root = int(rng() % N);       if (check_interesting(root)) break;       root = -1;     }     if (root < 0) {       cout << -1 <<   n ;       return;     }     vector<bool> bad(N, false);     for (int x : tour_list)       if (low_link[x][0] < tour_index[x] && low_link[x][1] < tour_index[x]) {         bad[x] = true;       } else {         assert(low_link[x][1] == tour_index[x]);         int above = tour_list[low_link[x][0]];         bad[x] = bad[above];       }     vector<int> interesting;     for (int i = 0; i < N; i++)       if (!bad[i]) interesting.push_back(i);     if (5 * int(interesting.size()) < N)       cout << -1 <<   n ;     else       output_vector(interesting, true);   }   int main() {     ios::sync_with_stdio(false);     cin.tie(nullptr);     int tests;     cin >> tests;     while (tests-- > 0) run_case();   }   