The SplHeap class
(PHP 5 >= 5.3.0)
Introduction
The SplHeap class provides the main functionalities of a Heap.
Class synopsis
/* Methods */
}Table of Contents
- SplHeap::compare — Compare elements in order to place them correctly in the heap while sifting up.
- SplHeap::__construct — Constructs a new empty heap
- SplHeap::count — Counts the number of elements in the heap.
- SplHeap::current — Return current node pointed by the iterator
- SplHeap::extract — Extracts a node from top of the heap and sift up.
- SplHeap::insert — Inserts an element in the heap by sifting it up.
- SplHeap::isEmpty — Checks whether the heap is empty.
- SplHeap::key — Return current node index
- SplHeap::next — Move to the next node
- SplHeap::recoverFromCorruption — Recover from the corrupted state and allow further actions on the heap.
- SplHeap::rewind — Rewind iterator back to the start (no-op)
- SplHeap::top — Peeks at the node from the top of the heap
- SplHeap::valid — Check whether the heap contains more nodes
Коментарии
To have a good idea what you can do with SplHeap, I created a little example script that will show the rankings of Belgian soccer teams in the Jupiler League.
<?php
/**
* A class that extends SplHeap for showing rankings in the Belgian
* soccer tournament JupilerLeague
*/
class JupilerLeague extends SplHeap
{
/**
* We modify the abstract method compare so we can sort our
* rankings using the values of a given array
*/
public function compare($array1, $array2)
{
$values1 = array_values($array1);
$values2 = array_values($array2);
if ($values1[0] === $values2[0]) return 0;
return $values1[0] < $values2[0] ? -1 : 1;
}
}
// Let's populate our heap here (data of 2009)
$heap = new JupilerLeague();
$heap->insert(array ('AA Gent' => 15));
$heap->insert(array ('Anderlecht' => 20));
$heap->insert(array ('Cercle Brugge' => 11));
$heap->insert(array ('Charleroi' => 12));
$heap->insert(array ('Club Brugge' => 21));
$heap->insert(array ('G. Beerschot' => 15));
$heap->insert(array ('Kortrijk' => 10));
$heap->insert(array ('KV Mechelen' => 18));
$heap->insert(array ('Lokeren' => 10));
$heap->insert(array ('Moeskroen' => 7));
$heap->insert(array ('Racing Genk' => 11));
$heap->insert(array ('Roeselare' => 6));
$heap->insert(array ('Standard' => 20));
$heap->insert(array ('STVV' => 17));
$heap->insert(array ('Westerlo' => 10));
$heap->insert(array ('Zulte Waregem' => 15));
// For displaying the ranking we move up to the first node
$heap->top();
// Then we iterate through each node for displaying the result
while ($heap->valid()) {
list ($team, $score) = each ($heap->current());
echo $team . ': ' . $score . PHP_EOL;
$heap->next();
}
?>
This results in the following output:
Club Brugge: 21
Anderlecht: 20
Standard: 20
KV Mechelen: 18
STVV: 17
Zulte Waregem: 15
AA Gent: 15
G. Beerschot: 15
Charleroi: 12
Racing Genk: 11
Cercle Brugge: 11
Kortrijk: 10
Lokeren: 10
Westerlo: 10
Moeskroen: 7
Roeselare: 6
Hope this example paved the way for more complex implementations of SplHeap.
While Michelangelo Van Dam example (http://br2.php.net/manual/en/class.splheap.php#93930) is a great demonstration of what can be done with SplHeap, this implementation is exactly what SplPriorityQueue does - based on SplMaxHeap. If you're planning to copy that snippet, go no further! There's a SPL class that does exactly what you want :)If you wish to build a true tree based heap, you can do so as follows (implemented with SplMinHeap, but could be SplMaxHeap if you wish for the opposite order of items):
The stucture that we're trying to represent:
1
|
+-----+--+--+-----+
| | | |
2 3 4 5
| | |
+ +-+-+ +
| | | |
7 6 8 9
|
+-+-+
| |
10 11
<?php
$h = new SplMinHeap();
// [parent, child]
$h->insert([9, 11]);
$h->insert([0, 1]);
$h->insert([1, 2]);
$h->insert([1, 3]);
$h->insert([1, 4]);
$h->insert([1, 5]);
$h->insert([3, 6]);
$h->insert([2, 7]);
$h->insert([3, 8]);
$h->insert([5, 9]);
$h->insert([9, 10]);
for ($h->top(); $h->valid(); $h->next()) {
list($parentId, $myId) = $h->current();
echo "$myId ($parentId)\n";
}
?>
As you iterate over the heap, the return data will be read as if you're reading a book; ie left to right, top to bottom. It will NOT follow the relationships.
So, the above code will output the following:
1 (0)
2 (1)
3 (1)
4 (1)
5 (1)
7 (2)
6 (3)
8 (3)
9 (5)
10 (9)
11 (9)