BFS

#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)
        {
            if(visited[*it]==false)
            {
                visited[*it]=true;
                que.push(*it);
            }
        }
}

    cout<<endl;
    return 0;
}