/**
* Merges two sorted linked lists non recursively
* @param DoubleLinkedList $first
* @param DoubleLinkedList $second
* @return DoubleLinkedList
*/
private function merge(DoubleLinkedList $first, DoubleLinkedList $second)
{
$listToReturn = new DoubleLinkedList();
if ($first === null) {
$listToReturn = $second;
} elseif ($second === null) {
$listToReturn = $first;
} else {
while (!$first->isEmpty() && !$second->isEmpty()) {
if ($first->getBottom()->getData() < $second->getBottom()->getData()) {
$listToReturn->push($first->getBottom()->getData());
$first->delete();
} else {
$listToReturn->push($second->getBottom()->getData());
$second->delete();
}
}
while (!$first->isEmpty()) {
$listToReturn->push($first->getBottom()->getData());
$first->delete();
}
while (!$second->isEmpty()) {
$listToReturn->push($second->getBottom()->getData());
$second->delete();
}
}
return $listToReturn;
}
