php实现双向队列

<?php

class Deque {

    private $queue = array();

    public function addFirst($item) {
        return array_unshift($this->queue, $item);
    }

    public function addLast($item) {
        return array_push($this->queue, $item);
    }

    public function removeFirst() {
        return array_shift($this->queue);
    }

    public function removeLast() {
        return array_pop($this->queue);
    }

}