Organize linked list into groups of even and odd nodes in php

Php program for Organize linked list into groups of even and odd nodes. Here problem description and explanation.

<?php
/*
    Php program for
    Grouping of even and odd nodes in linked list
*/
// Linked list node
class LinkNode
{
	public $data;
	public $next;
	public	function __construct($data)
	{
		$this->data = $data;
		$this->next = NULL;
	}
}
class SingleLL
{
	public $head;
	public	function __construct()
	{
		$this->head = NULL;
	}
	// Adding new node at beginning of linked list
	public	function insert($data)
	{
		// Create new node
		$node = new LinkNode($data);
		// Connect current node to head
		$node->next = $this->head;
		$this->head = $node;
	}
	// Display linked list element
	public	function display()
	{
		if ($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";
	}
	// Arrange alternative even and odd nodes in linked list
	public	function arrangeEvenOdds()
	{
		// Define some auxiliary variables
		$even_node = NULL;
		$odd_node = NULL;
		$tail_1 = NULL;
		$tail_2 = NULL;
		$auxiliary = $this->head;
		$this->head = NULL;
		// Segregation of even and odd nodes elements
		while ($auxiliary != NULL)
		{
			if ($auxiliary->data % 2 == 0)
			{
				// Even Node element
				if ($even_node == NULL)
				{
					$even_node = $auxiliary;
				}
				else
				{
					// Add node at end of even list
					$tail_1->next = $auxiliary;
				}
				// Get new last node
				$tail_1 = $auxiliary;
				// visit to next node
				$auxiliary = $auxiliary->next;
				// set next node is null
				$tail_1->next = NULL;
			}
			else
			{
				// Odd Node element
				if ($odd_node == NULL)
				{
					$odd_node = $auxiliary;
				}
				else
				{
					// Add node at end of odd list
					$tail_2->next = $auxiliary;
				}
				// Get new last node
				$tail_2 = $auxiliary;
				// visit to next node
				$auxiliary = $auxiliary->next;
				// set next node is null
				$tail_2->next = NULL;
			}
		}
		if ($even_node != NULL)
		{
			// new first node of linked list
			$this->head = $even_node;
		}
		else
		{
			// When only odd element exists in linked list
			$this->head = $odd_node;
		}
		// Combine even and odd nodes
		while ($even_node != NULL && $odd_node != NULL)
		{
			// next node of even list
			$tail_1 = $even_node->next;
			// next node of odd list
			$tail_2 = $odd_node->next;
			$even_node->next = $odd_node;
			if ($tail_1 != NULL)
			{
				// This is useful to handle 
				// when even linked list next node is empty 
				// and odd elements are next node not empty.
				$odd_node->next = $tail_1;
			}
			// Visit to next node
			$even_node = $tail_1;
			$odd_node = $tail_2;
		}
	}
	public static
	function main($args)
	{
		$list1 = new SingleLL();
		$list2 = new SingleLL();
		$list3 = new SingleLL();
		// Create linked list1
		$list1->insert(8);
		$list1->insert(2);
		$list1->insert(9);
		$list1->insert(7);
		$list1->insert(3);
		$list1->insert(10);
		$list1->insert(5);
		$list1->insert(4);
		$list1->insert(6);
		// Create linked list2
		$list2->insert(1);
		$list2->insert(1);
		$list2->insert(4);
		$list2->insert(2);
		$list2->insert(3);
		$list2->insert(1);
		// Create linked list3
		$list3->insert(2);
		$list3->insert(3);
		$list3->insert(3);
		$list3->insert(8);
		$list3->insert(4);
		$list3->insert(6);
		$list3->insert(2);
		// Test A
		echo " Before arrange : \n";
		// Before arrange nodes
		$list1->display();
		// Case A
		// When linked list contains same length of 
		// Even and Odd nodes
		$list1->arrangeEvenOdds();
		echo " After arrange  : \n";
		// After arrange nodes
		$list1->display();
		// Test B
		echo "\n Before arrange : \n";
		// Before arrange nodes
		$list2->display();
		// Case B
		// When linked list Odd nodes are more than Even
		$list2->arrangeEvenOdds();
		echo " After arrange  : \n";
		// After arrange nodes
		$list2->display();
		// Test C
		echo "\n Before arrange : \n";
		// Before arrange nodes
		$list3->display();
		// Case C
		// When linked list Odd nodes are more than Even
		$list3->arrangeEvenOdds();
		echo " After arrange  : \n";
		// After arrange nodes
		$list3->display();
	}
}
SingleLL::main(array());

Output

 Before arrange :
 6 → 4 → 5 → 10 → 3 → 7 → 9 → 2 → 8 → NULL
 After arrange  :
 6 → 5 → 4 → 3 → 10 → 7 → 2 → 9 → 8 → NULL

 Before arrange :
 1 → 3 → 2 → 4 → 1 → 1 → NULL
 After arrange  :
 2 → 1 → 4 → 3 → 1 → 1 → NULL

 Before arrange :
 2 → 6 → 4 → 8 → 3 → 3 → 2 → NULL
 After arrange  :
 2 → 3 → 6 → 3 → 4 → 8 → 2 → NULL