class Deque{
private $queue = [];
public function addFirst($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);
}
}
array_unshift | array_push 返回子元素个数
array_shift | array_pop 弹出元素值
