func_code_string: #include <bits/stdc++.h>   using namespace std;   unsigned long long mod = 1e9 + 7;   int n, m;   vector<int> depth;   vector<bool> visited;   vector<vector<int>> adj;   void dfs(int curr, int dt) {     depth[curr] = (dt) % 2;     visited[curr] = true;     for (int i = 0; i < adj[curr].size(); i++) {       if (!visited[adj[curr][i]]) {         dfs(adj[curr][i], dt + 1);       }     }   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     int t;     cin >> t;     while (t--) {       cin >> n >> m;       adj = vector<vector<int>>(n + 1);       depth = vector<int>(n + 1);       visited = vector<bool>(n + 1, false);       for (int i = 0; i < m; i++) {         int x, y;         cin >> x >> y;         adj[x].push_back(y);         adj[y].push_back(x);       }       dfs(1, 0);       vector<int> v1;       vector<int> v2;       for (int i = 1; i <= n; i++) {         if (depth[i] % 2) {           v1.push_back(i);         } else {           v2.push_back(i);         }       }       if (v1.size() < v2.size()) {         cout << v1.size() << endl;         for (int i = 0; i < v1.size(); i++) {           cout << v1[i] <<    ;         }       } else {         cout << v2.size() << endl;         for (int i = 0; i < v2.size(); i++) {           cout << v2[i] <<    ;         }       }       cout << endl;     }   }   