Queue

Programming basics

In computer science, a queue is a particular kind of abstract data type or collection in which the entities in the collection are kept in order and the principal (or only) operations on the collection are the addition of entities to the rear terminal position, known as enqueue, and removal of entities from the front terminal position, known as dequeue. This makes the queue a First-In-First-Out (FIFO) data structure. In a FIFO data structure, the first element added to the queue will be the first one to be removed. This is equivalent to the requirement that once a new element is added, all elements that were added before have to be removed before the new element can be removed. Often a peek or front operation is also entered, returning the value of the front element without dequeuing it. A queue is an example of a linear data structure, or more abstractly a sequential collection.

Image of a queue

Access methods of a queue

• enqueue
• dequeue
• isEmpty
• peek

Practical applications of queue's

• Printer queues
• Computer modelling of physical queues (like in a supermarket)

Queue - video example

This video provides a basic introduction to queues

Priority Queue

In computer science, a priority queue is an abstract data type which is like a regular queue or stack data structure, but where additionally each element has a "priority" associated with it. In a priority queue, an element with high priority is served before an element with low priority. If two elements have the same priority, they are served according to their order in the queue..

A python learning activity

Using the python list data structure, implement 4 queue functions, enqueue, dequeue, peek and isEmpty. We assume we know the name of the queue.

myQueue = []

def enqueue(element):

    # do stuff here

    return

def dequeue(element):

    # do stuff here

    return

def peek(element):

    # do stuff here

    return

def isEmpty(stackName):

    # this function should return as boolean True or False
    return 

# for extra challenge create a priority queue.

Standards

• Describe the characteristics and applications of a queue.
• Construct algorithms using the access methods of a queue.
• Explain the use of arrays as static stacks and queues.

See Also

• Abstract data structures

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