A note on top() and bottom():

Picture the doubly-linked list (or queue) in the same way that you would a stack.

Say you started with an empty queue, and added five values:

$myList = new SplDoublyLinkedList

$mylist->push(1)
$mylist->push(2)
$mylist->push(3)
$mylist->push(4)
$mylist->push(5)

$mylist->top()
-> 5

$mylist->bottom()
-> 1

<?php

/*
 * Examples of DoublyLinkedList
 */

$obj = new SplDoublyLinkedList();

// Check wither linked list is empty
if ($obj->isEmpty())
{
    echo "Adding nodes to Linked List<br>";
    $obj->push(2);
    $obj->push(3);
    
    echo "Adding the node at beginning of doubly linked list <br>";
    $obj->unshift(10);
}

echo "<br>Our Linked List:";
print_r($obj);

echo "<br>Pick the node from beginning of doubly linked list";
echo $obj->bottom();

?>