我最近正在解决非常类似的问题，似乎 SPL 不支持更新。所以
我不得不写我自己的堆。
它效率不高，但它可以满足我的需要，并且比重复排序数组要快得多……尽管 SPL 堆仍然快得多……
这里是...
class heap
{
public $members=array();
// these two are just for statistics
private $swaps=0;
private $recurs=array('lups'=>0, 'ldowns'=>0);
public function insert($val){
if(is_array($val) && empty($this->members)){ // because heapify is (in theory) more efficient
foreach($val as $v){
$this->members[]=$v;
}
$this->heapify();
}else{
$emptyPosition=count($this->members); // count(members) gets index of first empty position, not last key
$this->members[]=$val; // puts $val in
$this->ladderup($emptyPosition);
}
}
public function heapify(){
/* in case all the heap is broken, we can always use this to repair it.
It should be more efficient to fill $members randomly and "repair" it with heapify after,
than inserting things one by one*/
$start=max(0, floor( (count($this->members)-1)/2)); // find last parent
for($i=$start;$i>=0;$i--){
$this->ladderdown($i);
}
}
private function ladderdown($index){
// recursively sifts down $index
$this->recurs['ldowns']++;
/*
indexes of children
they are stored at parent_position*2 and parent_position*2+1
but becouse php uses null-based array indexing, we have to modify it a little
*/
$iA=$index*2+1;
$iB=$index*2+2;
if($iA<count($this->members)){ // check if children exist
if($iB<count($this->members)){
if($this->compare($iA, $iB)>=0) $bigger=$iA; // if both exist, compare them, cause we want to swap with the bigger one ; I'm using ">=" here, that means if they're equal, left child is used
else $bigger=$iB;
}else{
$bigger=$iA; // if only one children exists, use it
}
if($this->compare($bigger, $index)>0){ // not using ">=" here, there's no reason to swap them if they're same
$this->swap($bigger, $index);
$this->ladderdown($bigger); // continue with $bigger because that's the position, where the bigger member was before we swap()ped it
}
}
}
private function ladderup($index){
// sift-up,
$this->recurs['lups']++;
$parent=max(0, floor( ($index-1)/2)); // find parent index; this way it actualy swaps one too many times: at the end of sift-up-ing swaps the root with itself
if($this->compare($index, $parent)>0){
$this->swap($index, $parent);
$this->ladderup($parent);
}
}
public function root(){
if(count($this->members)){
return $this->members[0];
}
return false;
}
public function extract(){
// removes and returns root member
if(!count($this->members)) return false;
$this->swap(0,count($this->members)-1); // swaps root with last member
$result=array_pop($this->members); // removes last member (now root)
$this->ladderdown(0); // root is on wrong position, sifts it down
return $result;
}
public function update($index, $value){
if($index<count($this->members)){
$this->members[$index]=$value;
$this->ladderup($index);
$this->ladderdown($index);
}
}
public function delete($index){
// removes index from heap the same way as root is extracted
$this->swap(count($this->members)-1, $index); // swaps index with last one
array_pop($this->members);
$this->ladderup($index);
$this->ladderdown($index);
}
private function swap($iA, $iB){
// swaps two members
$this->swaps++;
$swap=$this->members[$iA];
$this->members[$iA]=$this->members[$iB];
$this->members[$iB]=$swap;
}
private function compare($iA, $iB){
$result=$this->members[$iA] - $this->members[$iB];
return $result;
}
public function stats($text=""){
// prints and resets statistics
echo "STATS: $text... Sift-ups: ".$this->recurs['lups']." Sift-downs: ".$this->recurs['ldowns']." Swaps: ".$this->swaps." <br>";
$this->recurs=array('lups'=>0, 'ldowns'=>0);
$this->swaps=0;
}
}
//here's how to use it...
$h=new heap;
for($i=0; $i<10000; $i++){
$h->insert(rand(1,1000));
}
$h->stats("after inserting one-by-one");
while($biggest=$h->extract()); // note that $h->extract might return FALSE, but might return zero as well, if there was zero in the heap
$h->stats("after extracting all roots (like in heapsort)");
echo "Now, heap is empty. Let's try whole array at once <br>";
for($i=0; $i<10000; $i++){
$a[]=rand(1,1000);
}
$h->insert($a); // inserting whole array here, so heap will use more efficient heapify()
$h->stats("after heapify");
echo "let's update two indexes<br>";
$h->update(1234,44444);// sure on top
$h->stats("after update");
$h->update(8888,40000);// second place
$h->stats("after update");
echo "extract biggest three indexes<br>";
echo $h->extract()." - this should be 44444<br>";
echo $h->extract()." - this should be 40000<br>";
echo $h->extract()." - this should be biggest number given by rand(1,1000)<br>";
$h->stats("after three extracts");
while($h->extract());
$h->stats("after extracting the rest");
结果是：
STATS：一一插入后... Sift-ups：22651 Sift-downs：0 Swaps：12651
STATS：提取所有根后（如在堆排序中）... Sift-ups：0 Sift-downs：116737 Swaps : 116737
现在，堆是空的。让我们一次尝试整个数组
STATS：heapify 后... Sift-ups：0 Sift-downs：12396 Swaps：7396
让我们更新两个索引
STATS：更新后... Sift-ups：11 Sift-downs：1 Swaps：10
统计：更新后... 筛选：13 筛选：1 交换：12
提取最大的三个索引
44444 - 这应该是 44444
40000 - 这应该是 40000
1000 - 这应该是 rand(1,1000) 给出的最大数字)
统计数据：经过三次提取...筛选：0 筛选：42 交换：42
统计：提取其余部分后...筛选：0 筛选：116652 交换：116652
您将不得不对其进行一些修改，但无论如何，希望它有所帮助..