BFS

#include <bits/stdc++.h>
using namespace std;

void bfs(vector<vector<int> > &adj){
    vector<int> visited(adj.size(), false);
    queue<int> q;

    int source = 1;
    q.push(source);
    visited[source] = true;

    while(!q.empty()){
        //take out the front node in queue
        int front = q.front();

        //pop the front
        q.pop();

        //print
        cout << front << " ";

        for(int i = 0; i < adj[front].size(); i++){
            int node = adj[front][i];
            if(!visited[node]){
                q.push(node);
                visited[node] = true;
            }
        }

    }
}

int main() {
    // your code goes here
    int n, m;
    cin >> n >> m;

   vector<vector<int> > adj(n + 1, vector<int>());

   for(int i = 0; i < m; i++){
       int u, v;
       cin >> u >> v;
       adj[u].push_back(v);
       adj[v].push_back(u);
   }

   bfs(adj);

}