A deque is very much like a
vector: like vector,it is a sequence
that supports random access to
elements,constant time insertion and
removal of elements at the end of the
sequence,and linear time insertion and removal of elements in the middle.

… deque also supports constant time insertion and removal of elements at the beginning of the sequence

所以因为它可以从两端有效地添加/删除,所以deque可以有效地用作其push_back和pop_front方法的队列：

std::deque<int> aDeque;

// enqueue
aDeque.push_back(1);
aDeque.push_back(2);

// dequeue
int top = aDeque.front();
aDeque.pop_front();

Accessing elements like an array means using the subscript operator

deque还支持通过下标运算符的随机访问：

std::cout << aDeque[0];