php实现堆排序

针对堆排序的概念自己百度去，今天没事了用php实现堆排序的算法

 1 abstract class Heap {
 2     protected $elements = array();
 3     protected $n = 0;
 4     
 5     public abstract function insert($element);
 6 
 7     public function isEmpty() {
 8         return $this->n==0;
 9     }
10     
11     public function all(){
12         return $this->elements;
13     }
14 
15     /**
16      * Extract the top value of the heap
17      *
18     */
19     public function extract() {
20         $element = $this->elements[1];
21         $this->elements[1] = array_pop($this->elements);
22         $this->n--;
23         $this->siftDown();
24         return $element;
25     }
26     
27     /**
28      * Rearranges the heap after an extraction to keep the heap property
29      */
30     protected abstract function siftDown();
31 
32     /**
33      * Swap two elements on the elements array
34      *
35      */
36     protected function swap($x,$y) {
37         $tmp = $this->elements[$x];
38         $this->elements[$x] = $this->elements[$y];
39         $this->elements[$y] = $tmp;
40     }
41 }
42 class MinHeap extends Heap {
43     
44     public function insert($element) {
45         $this->elements[++$this->n] = $element;
46         for ($i = $this->n; $i > 1 && $this->elements[$i >> 1] > $this->elements[$i]; $i = $i >> 1)
47             $this->swap($i >> 1,$i);
48     }
49     protected function siftDown() {
50         for ($i = 1; ($c = $i * 2) $this