The deque data structure

The deque data structure, also known as the double-ended queue, is a special queue that allows us to insert and remove elements from the end or from the front of the queue. 

An example of a deque in real life is the typical line for movie theaters, cafeterias, and so on. For example, a person who has just bought a ticket can come back to the front of the queue just to ask for some quick information. And if the person who is at the back of the queue is in a hurry, this person can also leave the queue.

In computer science, a common application of a deque is storing a list of undo operations. Each time a user performs an operation in the software, the operation is pushed to the deque (just like in a stack). When the user clicks on the Undo button, the operation is popped from the deque, meaning it is removed from the back. After a predefined number...