A deque is an ADT that generalizes a queue, allowing insertions and deletions at both ends. The C$++$ STL $($standard template library$)$ has a list class which provides this capability, using a linked list implementation. $($It is described in Chapter $3,$ but is not required reading at this time.$)$ For this assignment, you are to complete a simple implementation of an array$-$based deque. The implementation uses the "circular array" scheme, as in the array$-$based queue implementation we sketched in class. In the queue implementation, as elements are added or removed from the queue, the current queue contents "move" toward larger indices, so the front and back indexes into the array wrap around when they reach the "upper" end of the array. In an array$-$based deque, the collection of queue elements can "move" either direction. So$,$ for the deque implementation, you need look after wrapping around at both ends of the array: at the "upper" end just as in the queue, and also at the "lower" end. The reserve function also requires more care in the deque case.