Lorenzo Alberton

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PHP 5.3 SPL data structures: SplStack, SplHeap, SplPriorityQueue, SplDoublyLinkedList

Abstract: A sneak peak at some new SPL data structures (stack, heap, queue, list) introduced in PHP 5.3.


Following my recent experiments with the new SPL features in PHP 5.3, I saw that there are some new SPL data structures: heap, stack, queue and linked list. They aren't documented yet but I had a peek at the C sources.

SplStack

The first class, SplStack, is a standard implementation of a stack (duh!).

$stack = new SplStack();
 
$stack->push('b');
$stack->push('a');
$stack->push('c');
 
echo $stack->pop()."\n";
echo $stack->pop()."\n";
echo $stack->pop()."\n";
 
// OUTPUT:
// c
// a
// b

SplHeap

The second class is SplHeap, which is an abstract class and can't be instantiated directly. Two of its child classes are SplMinHeap (which sorts the data in descending order) and SplMaxHeap (which sorts the data in ascending order).

$heap = new SplMaxHeap();
$heap->insert('b');
$heap->insert('a');
$heap->insert('c');
 
echo $heap->extract()."\n";
echo $heap->extract()."\n";
echo $heap->extract()."\n";
 
// OUTPUT:
// c
// b
// a
$heap = new SplMinHeap();
$heap->insert('b');
$heap->insert('a');
$heap->insert('c');
 
echo $heap->extract()."\n";
echo $heap->extract()."\n";
echo $heap->extract()."\n";
 
// OUTPUT:
// a
// b
// c

Another SplHeap-derived class is SplPriorityQueue, which sorts the data by priority. With the setExtractFlags() method, you can choose what to extract:

  • EXTR_DATA (only the data)
  • EXTR_PRIORITY: only the priority value
  • EXTR_BOTH: both (array)

$pqueue = new SplPriorityQueue();
$pqueue->setExtractFlags(SplPriorityQueue::EXTR_DATA);
 
$pqueue->insert('low',    1);
$pqueue->insert('top',    3);
$pqueue->insert('medium', 2);
 
echo 'TOP ELEMENT: '.$pqueue->top()."\n";
echo $pqueue->extract()."\n";
echo $pqueue->extract()."\n";
echo $pqueue->extract()."\n";
 
// OUTPUT:
// TOP ELEMENT: top
// top
// medium
// low

SplDoublyLinkedList

$list = new SplDoublyLinkedList();
$list->push('a');
$list->push('b');
$list->push('c');
 
echo 'TOP: '.$list->top()."\n";
echo 'BOTTOM: '.$list->bottom()."\n";
 
// OUTPUT:
// TOP: c
// BOTTOM: a
 
echo "FIFO:\n";
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO);
for ($list->rewind(); $list->valid(); $list->next()) {
    echo $list->current()."\n";
}
 
// OUTPUT:
// FIFO:
// a
// b
// c
 
echo "LIFO:\n";
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO);
for ($list->rewind(); $list->valid(); $list->next()) {
    echo $list->current()."\n";
}
 
// OUTPUT:
// LIFO:
// c
// b
// a


2 responses to "PHP 5.3 SPL data structures: SplStack, SplHeap, SplPriorityQueue, SplDoublyLinkedList"

OriginalCopy, 19 January 2010 18:04

Hi.
It seems you know how to work with the \"new\" SPL classes. I\'m wondering if you could write an article with a solution to this one: http://stackoverflow.com/questions/2095680/, and make a blog entry out of it.
I\'ll keep an eye on your blog
Yours, Flavius

Matthew Setter, 14 April 2010 16:08

lorenzo,
cheers for the info. the SplPriorityQueue will definitely be used in a new project of mine.
Matt


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