Find top three elements of binary tree in php

Php program for Find top three elements of binary tree. Here mentioned other language solution.

<?php
/* 
  Php program for
  Find top three elements in binary tree
*/
// Node of Binary Tree
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 $first;
	public $second;
	public $third;
	public	function __construct()
	{
		$this->root = NULL;
		$this->first = NULL;
		$this->second = NULL;
		$this->third = NULL;
	}
	// Recursive function
	// Display preorder view of binary tree
	public	function preOrder($node)
	{
		if ($node != NULL)
		{
			//Print node value
			echo "  ".strval($node->data);
			$this->preOrder($node->left);
			$this->preOrder($node->right);
		}
	}
	// Find top three largest nodes in binary tree
	public	function getTopThree($node)
	{
		if ($node != NULL)
		{
			if ($this->first == NULL)
			{
				// First node of tree
				$this->first = $node;
			}
			else if ($this->first->data < $node->data)
			{
				// When get new first largest node
				// Interchange the node values
				$this->third = $this->second;
				$this->second = $this->first;
				$this->first = $node;
			}
			else if ($this->second == NULL)
			{
				if ($this->first->data != $node->data)
				{
					// Get second largest node
					$this->second = $node;
				}
			}
			else
			{
				if ($this->second->data < $node->data && 
                    $this->first->data > $node->data)
				{
					// When we get new second largest
					// Replace the third node with the second node
					$this->third = $this->second;
					// This is new second largest element
					$this->second = $node;
				}
				else if ($this->third == NULL)
				{
					if ($this->second->data > $node->data && 
                        $this->first->data > $node->data)
					{
						// Get the third largest node
						$this->third = $node;
					}
				}
				else if ($this->third->data < $node->data && 
                         $this->first->data > $node->data && 
                         $this->second->data > $node->data)
				{
					$this->third = $node;
				}
			}
			// Recursively, execute left and right subtree
			$this->getTopThree($node->left);
			$this->getTopThree($node->right);
		}
	}
	// This are handle the request to finding
	// top three nodes in binary tree.
	public	function printTopThree()
	{
		if ($this->root == NULL)
		{
			return;
		}
		// Display tree elements
		echo "\n Preorder : ";
		$this->preOrder($this->root);
		// Set the initial all three nodes
		$this->first = NULL;
		$this->second = NULL;
		$this->third = NULL;
		// Find three largest element
		$this->getTopThree($this->root);
		// Display calculated result
		echo "\n First : ".($this->first->data), "\n";
		if ($this->second != NULL && 
            $this->second != $this->first && 
            $this->second->data < $this->first->data)
		{
			echo " Second : ".($this->second->data), "\n";
		}
		else
		{
			echo " Second : None \n";
		}
		if ($this->third != NULL && 
            $this->third != $this->second && 
            $this->third != $this->first && 
            $this->third->data < $this->second->data)
		{
			echo " Third : ".($this->third->data), "\n";
		}
		else
		{
			echo " Third : None\n";
		}
	}
	public static function main()
	{
		// Create two trees
		$x = new BinaryTree();
		$y = new BinaryTree();
		/*
		    Construct Binary Tree
		    -----------------------
		           10
		          /  \
		         /    \
		        6      8
		       / \    / \
		      12  3  7   5
		     /        \   \
		    9         -6  13
		*/
		// Add nodes
		$x->root = new TreeNode(10);
		$x->root->left = new TreeNode(6);
		$x->root->left->left = new TreeNode(12);
		$x->root->right = new TreeNode(8);
		$x->root->right->right = new TreeNode(5);
		$x->root->right->left = new TreeNode(7);
		$x->root->right->left->right = new TreeNode(-6);
		$x->root->left->right = new TreeNode(3);
		$x->root->left->left->left = new TreeNode(9);
		$x->root->right->right->right = new TreeNode(13);
		/*
		    Construct Tree
		    --------------
		         1
		        / \ 
		       /   \
		      1     2
		     /     / \
		    1     2   2
		*/
		// Add second tree node
		$y->root = new TreeNode(1);
		$y->root->left = new TreeNode(1);
		$y->root->right = new TreeNode(2);
		$y->root->right->right = new TreeNode(2);
		$y->root->right->left = new TreeNode(2);
		$y->root->left->left = new TreeNode(1);
		// Test One
		$x->printTopThree();
		// Test Two
		$y->printTopThree();
	}
}
BinaryTree::main();

Output

 Preorder :   10  6  12  9  3  8  7  -6  5  13
 First : 13
 Second : 12
 Third : 10

 Preorder :   1  1  1  2  2  2
 First : 2
 Second : 1
 Third : None