默认容器为双端队列deque
常用的函数有：
- empty
- Test whether container is empty (public member function )
- size
- Return size (public member function )
- front
- Access next element (public member function )
- back
- Access last element (public member function )
- push
- Insert element (public member function )
- emplace
- Construct and insert element (public member function )
- pop
- Remove next element (public member function )