The SplDoublyLinkedList class

FIFO and LIFO in SplDoublyLinkedList
$list = new SplDoublyLinkedList();
$list->push('a');
$list->push('b');
$list->push('c');
$list->push('d');
 
echo "FIFO (First In First Out) :\n";
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO);
for ($list->rewind(); $list->valid(); $list->next()) {
 echo $list->current()."\n";
}
 
Result :
// FIFO (First In First Out):
// a
// b
// c
// d
 
echo "LIFO (Last In First Out) :\n";
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO);
for ($list->rewind(); $list->valid(); $list->next()) {
 echo $list->current()."\n";
}
 
Result :
// LIFO (Last In First Out):
// d
// c
// b
// a

/*
php doubly link list is an amazing data structure ,doubly means you can traverse forward as well as backward, it can act as a deque(double ended queue) if you want it to,
here is how it works 
*/
//instantiating an object of doubly link list
$dlist=new SplDoublyLinkedList();
//a push inserts data at the end of the list 
$dlist->push('hiramariam');
$dlist->push('maaz');
$dlist->push('zafar');
/* the list contains
hiramariam
maaz
zafar
*/ 
//while an unshift inserts an object at top of the list
$dlist->unshift(1);
$dlist->unshift(2);
$dlist->unshift(3);
/* the list now contains
3
2
1
hiramariam
maaz
zafar
*/ 
//you can delete an item from the bottom of the list by using pop
$dlist->pop();
/* the list now contains
3
2
1
hiramariam
maaz
*/ 
//you can delete an item from the top of the list by using shift()
$dlist->shift();
/* the list now contains
2
1
hiramariam
maaz
*/ 
/* if you want to replace an item at particular index you can use a method named add , note that if you want to replace an item that does not exist , an exception will be thrown*/
$dlist->add(3 , 2.24);
/*
to go through the list we use a simple for loop, the rewind() method shown below point to the initials of the list depending on the iterator, a valid() method checks whether a list is still valid or not , meaning it ensures the loop does not go on and on after we reach the last data in the list , and the next() method simply points to the next data in the list.
*/
for($dlist->rewind();$dlist->valid();$dlist->next()){
 
 echo $dlist->current()."<br/>";
 }
echo "<br/>";
/*
To traverse backward 
*/
$dlist->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO);
for($dlist->rewind();$dlist->valid();$dlist->next()){
 
 echo $dlist->current()."<br/>";;
 }

<?php
$splDoubleLinkedList = new SplDoublyLinkedList();
$splDoubleLinkedList->push('a');
$splDoubleLinkedList->push('3');
$splDoubleLinkedList->push('v');
$splDoubleLinkedList->push('1');
$splDoubleLinkedList->push('p');
//First of all, we need rewind list
$splDoubleLinkedList->rewind();
//Use while, check if the list has valid node
while ($splDoubleLinkedList->valid()){
 //Print current node's value
 echo $splDoubleLinkedList->current()."\n";
 //Turn the cursor to next node
 $splDoubleLinkedList->next();
}
?>

$list = new SplDoublyLinkedList();
for ($i = 0; $i < 2000001; $i++) {
 $list->push($i);
}
$s = microtime(true);
//$res = $list->offsetGet(2000000); // spend 7 ms
$res = $list->offsetGet(0); // spend 0.07 ms
var_dump($res);
$e = microtime(true);
echo ($e - $s) * 1000;

A function which replaces some portion od doubly linked list (DLL) with items from specified array.
<?php
/**
 * Replace some portion (specified by index and length) of DLL with items
 * from the specified replacement array.
 */
public function dll_splice(
 \SplDoublyLinkedList $dll,
 int $start,
 int $length,
 array $replacement,
): void {
 if ($start < 0 || ($start + $length) > $dll->count()) {
 throw new \OutOfRangeException("Invalid range for splicing");
 }
 for ($i = 0; $i < $length; $i++) {
 $dll->offsetUnset($start);
 }
 foreach ($replacement as $item) {
 $dll->add($start, $item);
 }
}
?>

$a = new SplDoublyLinkedList;
$arr=[1,2,3,4,5,6,7,8,9];
for($i=0;$i<count($arr);$i++){
 $a->add($i,$arr[$i]);
}
$a->push(11); //push method
$a->add(10,12); //add method must with index
$a->shift(); //remove array first value
$a->unshift(1); //add first value
$a->rewind(); //initial from first 
echo "SplDoublyLinkedList array last/top value " . $a->top() ." \n";
echo "SplDoublyLinkedList array count value " . $a->count() ." \n";
echo "SplDoublyLinkedList array first/top value " . $a->bottom() . " \n\n";
while($a->valid()){ //check with valid method
 echo 'key ', $a->key(), ' value ', $a->current(),"\n"; //key and current method use here
 $a->next(); //next method use here
}
$a->pop(); //remove array last value
print_r($a);
$s=$a->serialize();
echo $s;
//Output
SplDoublyLinkedList array last/top value 12 
SplDoublyLinkedList array count value 11 
SplDoublyLinkedList array first/top value 1 
key 0 value 1
key 1 value 2
key 2 value 3
key 3 value 4
key 4 value 5
key 5 value 6
key 6 value 7
key 7 value 8
key 8 value 9
key 9 value 11
key 10 value 12
SplDoublyLinkedList Object
(
 [flags:SplDoublyLinkedList:private] => 0
 [dllist:SplDoublyLinkedList:private] => Array
 (
 [0] => 1
 [1] => 2
 [2] => 3
 [3] => 4
 [4] => 5
 [5] => 6
 [6] => 7
 [7] => 8
 [8] => 9
 [9] => 11
 )
)
i:0;:i:1;:i:2;:i:3;:i:4;:i:5;:i:6;:i:7;:i:8;:i:9;:i:11;