a "deque" is a data structure consisting of a list of items, on which the following operations are possible: push(x,d): insert item x on the front end of deque d. pop(d): remove the front item from deque d and return it. inject(x,d): insert item x on the rear end of deque d. eject(d): remove the rear item from deque d and return it. write routines to support the deque that take o(1) time per operation.

“双端队列（deque）”是一种数据结构，由一系列项组成，支持以下操作：push（x，d）：将项x插入队列d的前端，pop（d）：从队列d的前端删除项并返回它，inject（x，d）：将项x插入队列d的末尾，eject（d）：从队列d的末尾删除项并返回它。编写程序支持deque，并保证每个操作所需的时间为O（1）。