Convert a binary tree into a circular doubly linked list in php

Php program for Convert a binary tree into a circular doubly linked list. Here more information.

<?php
/* 
  Php program for
  Convert binary tree to circular doubly linked list
*/
// 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 BinaryTree
{
	public $root;
	public	function __construct()
	{
		$this->root = NULL;
	}
	// Reversibly converting a given tree to
	// Circular doubly linked list
	public	function changeLink($node, $l, $r)
	{
		if ($node != NULL)
		{
			// Visit left subtree with left and right node
			$this->changeLink($node->left, $l, $node);
			// Visit right subtree with left and right node
			$this->changeLink($node->right, $node, $r);
			if ($node->left == NULL)
			{
				// Set new leaf side node
				$node->left = $l;
				if ($l != NULL)
				{
					// Because circular doubly linked list
					// So setup right side node
					$l->right = $node;
				}
			}
			if ($node->right == NULL)
			{
				$node->right = $r;
				if ($r != NULL)
				{
					// So setup left side node
					$r->left = $node;
				}
			}
		}
	}
	// Handles the request of convert binary tree into
	// Circular doubly linked list
	public	function convertToCll()
	{
		if ($this->root == NULL)
		{
			// When empty tree
			return;
		}
		// Change node link
		$this->changeLink($this->root, NULL, NULL);
		$temp = $this->root;
		// Setup first new node
		while ($temp->left != NULL)
		{
			$temp = $temp->left;
		}
		// Make new root
		$this->root = $temp;
		// Find last node
		while ($temp->right != NULL)
		{
			$temp = $temp->right;
		}
		// Make circular linked list
		$temp->right = $this->root;
		$this->root->left = $temp;
	}
	// Display circular linked list elements
	public	function displayData()
	{
		// Get first node
		$temp = $this->root;
		echo "\n Circular List element from front to rear\n";
		while ($temp != NULL)
		{
			// Display node value
			echo "  ".strval($temp->data);
			// Visit to right node
			$temp = $temp->right;
			if ($temp == $this->root)
			{
				// Stop execution
				$temp = NULL;
			}
		}
		echo "\n Circular List element from rear to front\n";
		// Get last node
		$temp = $this->root->left;
		while ($temp != NULL)
		{
			// Display node value
			echo "  ",$temp->data;
			// Visit to left node
			$temp = $temp->left;
			if ($temp == $this->root->left)
			{
				// Stop execution
				$temp = NULL;
			}
		}
	}
	public static function main($args)
	{
		// Create a binary tree
		$tree = new BinaryTree();
		/*
		        -1
		       /   \
		      2     8
		     / \   / \
		    3  -3 6   5
		       /   \   \
		     -7     4  -6
		     /     / \
		    9     1  -2  
		         /
		        7 
		-----------------------
		      Binary Tree
		-----------------------
		*/
		$tree->root = new TreeNode(-1);
		$tree->root->left = new TreeNode(2);
		$tree->root->right = new TreeNode(8);
		$tree->root->left->left = new TreeNode(3);
		$tree->root->left->right = new TreeNode(-3);
		$tree->root->left->right->left = new TreeNode(-7);
		$tree->root->left->right->left->left = new TreeNode(9);
		$tree->root->right->left = new TreeNode(6);
		$tree->root->right->right = new TreeNode(5);
		$tree->root->right->left->right = new TreeNode(4);
		$tree->root->right->right->right = new TreeNode(-6);
		$tree->root->right->left->right->left = new TreeNode(1);
		$tree->root->right->left->right->right = new TreeNode(-2);
		$tree->root->right->left->right->left->left = new TreeNode(7);
		// Convert to circular doubly linked list
		$tree->convertToCll();
		// Display element
		$tree->displayData();
	}
}
BinaryTree::main(array());

Output

 Circular List element from front to rear
  3  2  9  -7  -3  -1  6  7  1  4  -2  8  5  -6
 Circular List element from rear to front
  -6  5  8  -2  4  1  7  6  -1  -3  -7  9  2  3