• Queues are very straightforward but are slightly more complicated than stacks
• Queues can be implemented in a number of different ways using the same data structure (i.e., with different algorithms)
• So, they are a good ADT to consider next

• When you add a person to the line they go to the back
• People are served from the front (first-in-first-out or FIFO)

Queue

Values:	Homogeneous elements of any type.
Operations:	Name/Operator Arguments Returns Constructor A new instance. enqueue/append element The element to add to the rear of the queue dequeue/serve The element at the front of the queue isEmpty true if the queue is empty and false o/w

In addition, if the stack has a "size limit", one could add an isFull() operation; some people add a peek() operation; and some people add a makeEmpty() operation.

• Enqueue/append to the rear
• Dequeue/serve from the front (index 0)
• "Shuffle" after each serve
• An Analogy: A normal waiting line

• Keep a "pointer" to the front and rear elements
• Move all of the elements down when space at the back runs out
• One Analogy: A waiting line in which the server moves (until space runs out)
• Another Analogy: A clock in which the ticks are on a line, not a circle

• Keep a "pointer" to the front and rear elements
• Have the "pointers" wrap around
• An Analogy: A circular waiting line in which the server moves