/**
* @param DoubleLinkedList $first
* @param DoubleLinkedList $second
* @return DoubleLinkedListNode|DoubleLinkedList
*/
private function append(DoubleLinkedList $first, DoubleLinkedList $second)
{
$listToReturn = new DoubleLinkedList();
if ($first->isEmpty()) {
$listToReturn = $second;
} elseif ($second->isEmpty()) {
$listToReturn = $first;
} else {
/** @var DoubleLinkedListNode $bottom */
$bottom = $second->getBottom();
$bottom->setPrev($first->getTop());
$first->getTop()->setNext($second->getBottom());
$listToReturn->setBottom($first->getBottom());
$listToReturn->setTop($second->getTop());
}
return $listToReturn;
}
