Untitled

// Online Java Compiler
// Use this editor to write, compile and run your Java code online

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;


class Main {
    public static void main(String[] args) {
Node node1=new Node(1);
        Node n2=new Node(2);
        Node n3=new Node(3);
        Node n4=new Node(4);
        n2.setLeft(n4);

        List<List<Integer>> list=new ArrayList<>();
        int count=0;
        node1.setLeft(n2);
        node1.setRight(n3);
        Queue<Node> queue=new LinkedList<>();
        queue.add(node1);

        List<Integer> list1=new ArrayList<>();
        while(!queue.isEmpty()){
            Node element=queue.poll();
            count--;
            if(element!=null)
            list1.add(element.data);
            if(queue.isEmpty()|| count==0){
                list.add(list1);
                list1=new ArrayList<>();
                count=list1.size()*2;
            }
            if(element!=null){
            queue.add(element.left);
            queue.add(element.right);
            }
        }

        System.out.println(list);

    }


}


class Node{
    public int data;
    public Node left;
    public Node right;

    public Node(int data){
        this.data=data;
    }

    public void setLeft(Node left) {
        this.left = left;
    }

    public void setRight(Node right) {
        this.right = right;
    }
}