BSF

#include<iostream>
#include<queue>
#include<vector>
using namespace std;
int main()
{
    int edges,a,b;
    vector<int>nodes[1000];
    cout<<"Enter the no of edges"<<endl;
    cin>>edges;
    for(int i=0; i<edges; i++)
    {
        cin>>a>>b;
        nodes[a].push_back(b);
        nodes[b].push_back(a);
    }

    cout<<endl;
    //Adj list representation
    for(int i=0; i<1000; i++)
    {
        if(!nodes[i].empty())
        {
            cout<<"[ "<<i<<" ]"<<"-->";
            for(vector<int>::iterator it=nodes[i].begin();
                    it!=nodes[i].end(); ++it)
            {
                cout<<*it<<"-->";
            }
            cout<<"NULL"<<endl;
        }
    }

    queue<int> que;
//initially que is empty
    bool visited[1000];
// mark all the vertices as not visited
    for(int i=0; i<1000; i++)
        visited[i]=false;

    int start;
    cout<<"\nEnter the starting node"<<endl;
    cin>>start;

//insert the starting node into the queue
    que.push(start);
//mark the starting node as visited
    visited[start]=true;


    cout<<"\nBFS Traversal\n";

    while(!que.empty())
    {
        //Dequeue a vertex from que and print it
        int front = que.front();
        cout<<front<<" ";
        que.pop();
// get all adjacent vertices of the dequeued vertex s
        // If an adjacent vertex has not been visited,
        //then mark it as visited
        // and enqueue it
        for(vector<int>::iterator it=nodes[front].begin();it!=nodes[front].end(); ++it)
        {
            //cout<<"it="<<*it<<endl;
            if(visited[*it]==false)
            {
                visited[*it]=true;
                que.push(*it);
            }
        }
    }

    cout<<endl;
    return 0;
}
/*
7
1 2
1 3
1 5
2 4
2 6
3 7
5 6
Enter the starting node
1
OUTPUT:
1 5 6 2 4 3 7
*/