func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 1000 * 1000 + 10;   vector<int> vec[N];   vector<int> d[2];   bool mark[N];   void dfs(int v, int hh) {     mark[v] = true;     d[hh].push_back(v);     for (int u : vec[v])       if (!mark[u]) dfs(u, 1 - hh);   }   int main() {     int o;     cin >> o;     while (o--) {       int n, m;       cin >> n >> m;       for (int i = 0; i < n; i++) vec[i].clear(), mark[i] = false;       ;       d[0].clear();       d[1].clear();       for (int i = 0; i < m; i++) {         int a, b;         cin >> a >> b;         a--, b--;         vec[a].push_back(b);         vec[b].push_back(a);       }       dfs(0, 0);       if ((int)d[0].size() > (int)d[1].size()) swap(d[0], d[1]);       cout << (int)d[0].size() << endl;       for (int a : d[0]) cout << a + 1 <<    ;       cout << endl;     }     return 0;   }   