php双向队列

队列是一种线性表，按照先进先出的原则进行
单向队列：只能从头进，从尾出
双向队列：头尾都可以进出

<?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);    
        }
    }
 ?>