Insert node at middle of linked list in php

Suppose we are inserted the following (1, 2, 3, 4, 5, 6, 7) node in a sequence. In this post are implement second approach.

<?php
// Php Program for
// Insert linked list element at middle position

// Linked list node
class LinkNode
{
    public $data;
    public $next;
    public  function __construct($data)
    {
        $this->data = $data;
        $this->next = NULL;
    }
}
class LinkedList
{
    public $head;
    // Class constructors
    public  function __construct()
    {
        $this->head = NULL;
    }
    // Insert node in middle position
    public  function insert($value)
    {
        // Create a new node
        $node = new LinkNode($value);
        if ($this->head == NULL)
        {
            // First node
            $this->head = $node;
        }
        else
        {
            $temp = $this->head;
            $middle = $this->head;
            // Find the middle node
            while ($temp->next != NULL && $temp->next->next != NULL)
            {
                $temp = $temp->next->next;
                $middle = $middle->next;
            }
            // Add node
            $node->next = $middle->next;
            $middle->next = $node;
        }
    }
    // Display linked list element
    public  function display()
    {
        if ($this->head == NULL)
        {
            return;
        }
        $temp = $this->head;
        // iterating linked list elements
        while ($temp != NULL)
        {
            printf("%s → ", $temp->data);
            // Visit to next node
            $temp = $temp->next;
        }
        printf("%s", "NULL\n");
    }
    public static function main($args)
    {
        $sll = new LinkedList();
        // Add node
        $sll->insert(1);
        $sll->insert(2);
        $sll->insert(3);
        $sll->insert(4);
        $sll->insert(5);
        $sll->insert(6);
        $sll->insert(7);
        // 1 → 3 → 5 → 7 → 6 → 4 → 2 → NULL
        $sll->display();
    }
}

LinkedList::main(array());

 1 → 3 → 5 → 7 → 6 → 4 → 2 → NULL