php 双向队列

<?php
class deque
{
public $queue  = array();
public $length = 0;

public function frontAdd($node){
array_unshift($this->queue,$node);
$this->countqueue();
}
public function frontRemove(){
$node = array_shift($this->queue);
$this->countqueue();
return $node;
}

public function rearAdd($node){
array_push($this->queue,$node);
$this->countqueue();
}

public function rearRemove(){
$node = array_pop($this->queue);
$this->countqueue();
return $node;
}

public function countqueue(){
$this->length = count($this->queue);
}
}
$fruit = new deque();
echo $fruit -> length;
$fruit -> frontAdd("Apple");
$fruit -> rearAdd("Watermelon");
echo '<pre>';
print_r($fruit);
echo '</pre>';
?>