#include<iostream>
#include<map>
#include<list>
#include<queue>
using namespace std;

template<typename T>
class graph{
map<T,list<T> >l;
public:
    void addEdge(int x, int y){
    l[x].push_back(y);
    l[y].push_back(x);
    }

    void bfs(T src){
        queue<T>q;
        map<int, bool>visited;

        q.push(src);
        visited[src] = true;

        while(!q.empty()){
            T node = q.front();
            q.pop();
            cout<<node<<" ";
            for(int nbr: l[node]){
                if(!visited[nbr]){
                    q.push(nbr);
                    //mark tht nbr as visited
                    visited[nbr] = true;
                }
            }
        }
    }

};
int main()
{
graph<int>g;
g.addEdge(0,1);
g.addEdge(1,2);
g.addEdge(2,3);
g.addEdge(3,4);
g.addEdge(4,5);
g.bfs(0);
return 0;}