Thought exercises

Queues

• Queues allow you to insert at one end and remove (dequeue) at the other. A deque is a double-ended queue: it allows you to insert or remove at either end. What are the merits of representing a deque as:
  • Fixed array
  • Singly linked list
  • Doubly linked list
  Can you draw a picture of how the addToFront(), removeFromFront(), addToBack(), and removeFromBack() would be implemented for each representation?

Stacks

• Obviously, it's possible to implement arbitrarily-sized stacks using lists (linked lists or dynamic arrays). However, lower-level forms are sometimes acceptable if we know the stack will remain less than an upper bound. Can you think of a way to implement two stacks, using a single array, so that the stacks will only be full if the total number of items in both stacks is equal to the total size of the array? Draw a picture.










• Imagine that we want to simulate a data tape with a single tape head. We can only read from, or write to, the location directly under the head. How can we use two stacks to simulate this tape? Draw a picture of the result. How do we move the tape head left or right?