BFS of graph

//BFS of graph

import java.util.*;
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);
            }

            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();
        }
    }
}

class Solution {
    public ArrayList<Integer> bfsOfGraph(int V, ArrayList<ArrayList<Integer>> adj) {
        ArrayList<Integer> bfs = new ArrayList<>();
        Queue<Integer> q = new LinkedList<>();
        boolean[] vis = new boolean[V];
        q.add(0);
        vis[0] = true;
        
        while(!q.isEmpty()) {
            int rem = q.remove();
            bfs.add(rem);
            
            for(int v : adj.get(rem)) {
                if(vis[v] == false) {
                    q.add(v);
                    vis[v] = true;
                }
            }
        }
        
        return bfs;
    }
}