说明：  实现fifo算法实现fifo算法实现fifo算法实现fifo算法v实现fifo算法实现fifo算法实现fifo算法v
(fifo is a good chengxufifo is a good chengxufifo is a good chengxufifo is a good chengxufifo is a good chengxufifo is a good chengxu)