delete odd numbers from linked list in php

Php program for delete odd numbers from linked list. Here problem description and other solutions.

<?php
// Php program for
// Delete odd nodes from linked list

// Node of Linked List
class LinkNode
{
	public $data;
	public $next;
	public	function __construct($data)
	{
		//Set node value
		$this->data = $data;
		$this->next = NULL;
	}
}
class SingleLL
{
	public $head;
	public $tail;
	public	function __construct()
	{
		$this->head = NULL;
		$this->tail = NULL;
	}
	// Add new node at the end of linked list
	public	function addNode($value)
	{
		// Create a new node
		$node = new LinkNode($value);
		if ($this->head == NULL)
		{
			$this->head = $node;
		}
		else
		{
			$this->tail->next = $node;
		}
		$this->tail = $node;
	}
	// Display linked list element
	public	function display()
	{
		if ($this->head == NULL)
		{
			return;
		}
		$temp = $this->head;
		// iterating linked list elements
		while ($temp != NULL)
		{
			echo $temp->data," → ";
			// Visit to next node
			$temp = $temp->next;
		}
		echo "null\n";
	}
	// Delete all odd key nodes in linked list
	public	function deleteOddNodes()
	{
		// Define some auxiliary variables
		$current = $this->head;
		$auxiliary = NULL;
		$back = NULL;
		// iterating linked list elements
		while ($current != NULL)
		{
			if ($current->data % 2 != 0)
			{
				// When get odd node
				$auxiliary = $current;
			}
			else
			{
				$back = $current;
			}
			// Visit to next node
			$current = $current->next;
			if ($auxiliary != NULL)
			{
				// When Deleted node exists
				if ($back == NULL)
				{
					// When front node is odd node
					// head visit to next node
					$this->head = $current;
				}
				else
				{
					// When deleting centralized node
					$back->next = $current;
				}
				if ($this->tail == $auxiliary)
				{
					// When delete last node
					// Set new tail
					$this->tail = $back;
				}
				// Unlink deleted node 
				$auxiliary->next = NULL;
				$auxiliary = NULL;
			}
		}
	}
	public static
	function main($args)
	{
		$sll = new SingleLL();
		// Add linked list node
		$sll->addNode(3);
		$sll->addNode(1);
		$sll->addNode(4);
		$sll->addNode(7);
		$sll->addNode(9);
		$sll->addNode(6);
		$sll->addNode(5);
		$sll->addNode(11);
		// Before effect
		echo "Before Delete Odd Key Nodes\n";
		// 3 → 1 → 4 → 7 → 9 → 6 → 5 → 11 → NULL
		$sll->display();
		// Perform delete operation
		$sll->deleteOddNodes();
		// After effect
		echo "After Delete Odd Key Nodes\n";
		// 4 → 6 → NULL
		$sll->display();
	}
}
SingleLL::main(array());

Output

Before Delete Odd Key Nodes
3 → 1 → 4 → 7 → 9 → 6 → 5 → 11 → null
After Delete Odd Key Nodes
4 → 6 → null