using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Node root=Node.NewNode(1);

        root.Left=Node.NewNode(10);

        root.Right=Node.NewNode(100);

        root.Left.Left=Node.NewNode(21);

        root.Left.Right=Node.NewNode(31);

        root.Right.Left=Node.NewNode(101);

        root.Right.Right=Node.NewNode(102);

        root.Left.Left.Right=Node.NewNode(23);

        root.Left.Right.Left=Node.NewNode(32);

        var output=Node.TraverseLeafNode(root);

    }

}

public class Node

{

    public int Key;

    public Node Left;

    public Node Right;

    public static Node NewNode(int value)

    {

        Node node=new Node();

        node.Key=value;

        node.Left=null;

        node.Right=null;

        return node;

    }

    public static List<Node> TraverseLeafNode(Node root)

    {

        List<Node> list=new List<Node>();

        Queue<Node> queue=new Queue<Node>();

        queue.Enqueue(root);

        while(queue.Count!=0)

        {

            int count=queue.Count;

            while(count>0)

            {

                Node node=new Node();

                node=queue.Peek();

                queue.Dequeue();

                if(node.Left==null && node.Right==null)

                {

                    list.Add(node);

                    Console.WriteLine(node.Key);

                }

                else

                {

                    if(node.Left!=null)

                        queue.Enqueue(node.Left);

                    if(node.Right!=null)

                        queue.Enqueue(node.Right);

                }

                count--;

            }

        }

        return list;

    }

}