/**

  * Class Deque

  * 使用PHP实现双向队列

  */

 class Deque{

     private $queue = array();

     public function addFirst($item){//头入队

         array_unshift($this->queue,$item);

     }

     public function addLast($item){//尾入队

         array_push($this->queue,$item);

     }

     public function removeFirst(){//头出队

         array_shift($this->queue);

     }

     public function removeLast(){//尾出队

         array_pop($this->queue);

     }

     public  function show(){//打印

         foreach($this->queue as $item){

             echo $item." ";

         }

         echo "<br/>";

     }

 }

 $deque = new Deque();

 $deque->addFirst(2);

 $deque->addLast(3);

 $deque->addLast(4);

 $deque->addFirst(5);

 $deque->show();