func_code_string: #include <bits/stdc++.h>   using namespace std;   void BFS(vector<vector<long long> > &graph, long long n,            vector<long long> &order) {     vector<long long> vis(n + 1);     set<long long> PQ;     PQ.insert(1);     while (!PQ.empty()) {       long long x = *PQ.begin();       PQ.erase(PQ.begin());       order.push_back(x);       vis[x] = 1;       for (long long i = 0; i < graph[x].size(); i++) {         if (vis[graph[x][i]] == 0) PQ.insert(graph[x][i]);       }     }   }   int main() {     long long n, m, i, j, k, l, w, u, v, t_sum = 0;     cin >> n >> m;     vector<vector<long long> > graph(n + 1);     for (i = 1; i <= m; i++) {       cin >> u >> v;       graph[u].push_back(v);       graph[v].push_back(u);     }     vector<long long> order;     BFS(graph, n, order);     for (i = 0; i < order.size(); i++) cout << order[i] <<    ;     return 0;   }   