func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = (int)1e6 + 5;   vector<int> adjList[N];   unordered_set<int> remaining;   bitset<N> inQ, nextToQ;   vector<int> ans;   void solve(int u) {     remaining.erase(u);     for (auto v : adjList[u]) {       remaining.erase(v);     }     if (!remaining.empty()) {       solve(*remaining.begin());     }     if (!nextToQ[u]) {       inQ[u] = 1;       nextToQ[u] = 1;       for (auto v : adjList[u]) {         nextToQ[v] = 1;       }       ans.push_back(u);     }   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int n, m;     cin >> n >> m;     for (int i = 0; i < m; i++) {       int u, v;       cin >> u >> v;       adjList[u].push_back(v);     }     for (int i = 1; i <= n; i++) {       remaining.insert(i);     }     solve(1);     cout << ans.size() << endl;     for (auto u : ans) {       cout << u <<    ;     }     cout << endl;   }   