Queues: enqueue, dequeue and pointers

Overview

Two pointers used with a linear queue, drawback of a simple linear queue held in an array and one way of avoiding wasted space in a linear queue.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a queue?

   Model answer

   A queue is a first in, first out data structure. Items join at the rear and leave from the front.

2. 2

   What does the enqueue operation do?

   Model answer

   An enqueue operation adds an item to the rear of the queue. The rear pointer then moves on by one position.

3. 3

   What does the dequeue operation do?

   Model answer

   A dequeue operation removes the item at the front of the queue. The front pointer then moves on by one position.

4. 4

   Name the two pointers used with a linear queue.

   Model answer

   A linear queue uses a front pointer and a rear pointer. The front marks the next item to leave and the rear marks the last item to join.

5. 5

   Give one use of a queue in a computer system.

   Model answer

   A printer spooler holds waiting documents in a queue. Jobs are printed in the order in which they were sent.

6. 6

   Why is a queue described as FIFO?

   Model answer

   The first item to join the queue is the first item to leave it. The order of arrival is preserved exactly.

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