construct a linked list from 2d matrix in php

Php program for construct a linked list from 2d matrix. Here more information.

<?php
// Php program for
// Construct a linked list from 2D matrix
class LinkNode
{
	public $data;
	public $next;
	public $down;
	public	function __construct($data)
	{
		$this->data = $data;
		$this->next = NULL;
		$this->down = NULL;
	}
}
class DoublyLinkedList
{
	public $head;
	public	function __construct()
	{
		$this->head = NULL;
	}
	public	function display()
	{
		if ($this->head == NULL)
		{
			echo "Empty linked list";
		}
		else
		{
			$front = $this->head;
			$right = NULL;
			while ($front != NULL)
			{
				$right = $front;
				while ($right != NULL)
				{
					echo strval($right->data).
					"  ";
					$right = $right->next;
				}
				echo "\n";
				// Visit to down node
				$front = $front->down;
			}
		}
	}
	public	function insertData($matrix, $rows, $cols)
	{
		// Some auxiliary variables
		$levelHead = NULL;
		$root = NULL;
		$perv = NULL;
		$i = 0;
		$j = 0;
		// Add first row elements into result list 
		while ($i < $cols)
		{
			if ($this->head == NULL)
			{
				// Add first node
				$this->head = new LinkNode($matrix[0][$i]);
				$levelHead = $this->head;
			}
			else
			{
				// next head
				$levelHead->next = new LinkNode($matrix[0][$i]);
				$levelHead = $levelHead->next;
			}
			$i++;
		}
		// Get first element    
		$levelHead = $this->head;
		$i = 1;
		// Add all the bottom element of each column
		while ($i < $rows)
		{
			$root = NULL;
			$perv = $root;
			while ($j < $cols)
			{
				$levelHead->down = new LinkNode($matrix[$i][$j]);
				if ($root == NULL)
				{
					$root = $levelHead->down;
					$perv = $root;
				}
				else
				{
					$perv->next = $levelHead->down;
					$perv = $levelHead->down;
				}
				$levelHead = $levelHead->next;
				$j++;
			}
			$levelHead = $root;
			// reset col
			$j = 0;
			// change row
			$i++;
		}
	}
	public static
	function main($args)
	{
		$dll = new DoublyLinkedList();
		// Create 2D metrix
		$matrix = array(
          array(1, 6, 9, 2, -9), 
          array(2, 5, -5, 7, 1), 
          array(3, 4, 1, 8, 2)
        );
		$rows = count($matrix);
		$cols = count($matrix[0]);
		$dll->insertData($matrix, $rows, $cols);
		$dll->display();
	}
}
DoublyLinkedList::main(array());

Output

1  6  9  2  -9
2  5  -5  7  1
3  4  1  8  2