func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<long long> gr[200011];   vector<long long> v;   vector<long long> v1;   bool vis[200011];   queue<pair<long long, bool> > q;   long long n, m;   void bfs(long long s, bool k) {     q.push({s, k});     while (!q.empty()) {       long long node = q.front().first;       bool z = q.front().second;       q.pop();       if (vis[node]) continue;       if (z)         v.push_back(node);       else         v1.push_back(node);       vis[node] = 1;       for (int i = 0; i < gr[node].size(); i++)         if (!vis[gr[node][i]]) q.push({gr[node][i], !z});     }   }   int main() {     ios::sync_with_stdio(0);     long long q, i, x, y;     cin >> q;     while (q--) {       cin >> n >> m;       for (i = 0; i < m; i++) {         cin >> x >> y;         gr[x].push_back(y);         gr[y].push_back(x);       }       v.clear();       v1.clear();       bfs(1, 0);       if (v.size() <= n / 2) {         cout << v.size() << endl;         for (i = 0; i < v.size(); i++) cout << v[i] <<    ;         cout << endl;       } else {         cout << v1.size() << endl;         for (i = 0; i < v1.size(); i++) cout << v1[i] <<    ;         cout << endl;       }       for (i = 1; i <= n; i++) {         vis[i] = 0;         gr[i].clear();       }     }     return 0;   }   