codeIIEST/Algorithms

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

vector<bool>Visited;
vector< vector<int> >Graph;

void edge(int a,int b)
{
    Graph[a].push_back(b); //for directed

    //If undirected graph is there, then add the following line
    // Graph[b].push_back(a);
}

void BreadthFirstSearch(int u)
{
    queue<int>q;
    q.push(u);
    Visited[u]=true;

    while(!q.empty())
    {
        int f=q.front();
        q.pop();

        cout<<f<<" ";
        int ln=Graph[f].size();
        for(int j=0;j<ln;j++)
        {
            if(!Visited[Graph[f][j]])
            {
                q.push(Graph[f][j]);
                Visited[Graph[f][j]]=true;
            }
        }
    }
}

int main()
{
    int n,e;
    cin>>n>>e;
    Visited.assign(n,false);
    Graph.assign(n,vector<int>());

    int a,b;
    for(int i=0;i<e;i++)
    {
        cin>>a>>b;
        edge(a,b);
    }

    for(int i=0;i<n;i++)
    {
        if(!Visited[i])
        {
            BreadthFirstSearch(i);
        }
    }
    return 0;
}