Level order traversal using queue in php

Php program for Level order traversal using queue. Here problem description and other solutions.

<?php
/*
  Php program for
  Level order tree traversal using queue
*/
// Create Q node
class QNode
{
	public $data;
	public $next;

	function __construct($node)
	{
		$this->data = $node;
		$this->next = NULL;
	}
}
// Binary Tree Node
class TreeNode
{
	public $data;
	public $left;
	public $right;
	public	function __construct($data)
	{
		// Set node value
		$this->data = $data;
		$this->left = NULL;
		$this->right = NULL;
	}
}
class MyQueue
{
	public $head;
	public $tail;
	public $count;
	public	function __construct()
	{
		$this->head = NULL;
		$this->tail = NULL;
		$this->count = 0;
	}
	public	function size()
	{
		return $this->count;
	}
	public	function isEmpty()
	{
		return $this->count == 0;
	}
	// Add new node of queue
	public	function enqueue($value)
	{
		// Create a new node
		$node = new QNode($value);
		if ($this->head == NULL)
		{
			// Add first element into queue
			$this->head = $node;
		}
		else
		{
			// Add node at the end using tail
			$this->tail->next = $node;
		}
		$this->count++;
		$this->tail = $node;
	}
	// Delete a element into queue
	function dequeue()
	{
		if ($this->head == NULL)
		{
			// Empty Queue
			return;
		}
		// Visit next node
		$this->head = $this->head->next;
		$this->count--;
		if ($this->head == NULL)
		{
			// When deleting a last node of linked list
			$this->tail = NULL;
		}
	}
	// Get front node
	public	function peek()
	{
		if ($this->head == NULL)
		{
			return NULL;
		}
		return $this->head->data;
	}
}
class BinaryTree
{
	public $root;
	public	function __construct()
	{
		$this->root = NULL;
	}
	public	function levelOrder()
	{
		if ($this->root != NULL)
		{
			$q = new MyQueue();
			// Add first node
			$q->enqueue($this->root);
			$node = $this->root;
			while ($q->isEmpty() == false && $node != NULL)
			{
				if ($node->left != NULL)
				{
					// Add left child node
					$q->enqueue($node->left);
				}
				if ($node->right != NULL)
				{
					// Add right child node
					$q->enqueue($node->right);
				}
				// Display level node
				echo "  ".strval($node->data);
				// Remove current node
				$q->dequeue();
				// Get new head
				$node = $q->peek();
			}
		}
		else
		{
			echo "Empty Tree", "\n";
		}
	}
	public static
	function main($args)
	{
		// Create new tree
		$tree = new BinaryTree();
		/*
		  Make A Binary Tree
		  -----------------------
		         1
		       /   \
		      2     3
		     /     / \
		    4     5   6
		   /     / \
		  7     8   9
		*/
		// Adding tree nodes
		$tree->root = new TreeNode(1);
		$tree->root->left = new TreeNode(2);
		$tree->root->right = new TreeNode(3);
		$tree->root->right->right = new TreeNode(6);
		$tree->root->right->left = new TreeNode(5);
		$tree->root->left->left = new TreeNode(4);
		$tree->root->left->left->left = new TreeNode(7);
		$tree->root->right->left->left = new TreeNode(8);
		$tree->root->right->left->right = new TreeNode(9);
		// Display level order  element
		$tree->levelOrder();
	}
}
BinaryTree::main(array());

Output

  1  2  3  4  5  6  7  8  9