BfsJava

import java.lang.*;
import java.io.*;
class GFG
{
    public static void main(String[] args) throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int T = Integer.parseInt(br.readLine().trim());
        while(T-->0)
        {
            String[] s = br.readLine().trim().split(" ");
            int V = Integer.parseInt(s[0]);
            int E = Integer.parseInt(s[1]);
            ArrayList<ArrayList<Integer>>adj = new ArrayList<>();
            for(int i = 0; i < V; i++)
                adj.add(i, new ArrayList<Integer>());
            for(int i = 0; i < E; i++){
                String[] S = br.readLine().trim().split(" ");
                int u = Integer.parseInt(S[0]);
                int v = Integer.parseInt(S[1]);
                adj.get(u).add(v);
                // adj.get(v).add(u);
            }
            Solution obj = new Solution();
            ArrayList<Integer>ans = obj.bfsOfGraph(V, adj);
            for (int i =0 ;i < ans.size (); i++) 
                System.out.print (ans.get (i) + " ");
            System.out.println();
        }
    }
}
// } Driver Code Ends


class Solution
{
    public ArrayList<Integer> bfsOfGraph(int V, ArrayList<ArrayList<Integer>> adj)
    {
        
        ArrayList<Integer> bfs = new ArrayList<>(); 
        boolean vis[] = new boolean[V]; 
        Queue<Integer> q = new LinkedList<>();
        
        q.add(0); 
        vis[0] = true; 
        
        while (!q.isEmpty())
        {
            Integer node = q.poll();
            bfs.add(node); 
 
            // Get all adjacent vertices of the dequeued vertex s
            // If a adjacent has not been visited, then mark it
            // visited and enqueue it
            for(Integer it: adj.get(node)) {
                if(vis[it] == false) {
                    vis[it] = true; 
                    q.add(it); 
                } 
            }
        }
        
        return bfs; 
        
        // Code here
    }
}