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# Lab Week 3: Queue implementations

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CPE 202  Lab Week 3.docx 1
Lab Week 3: Queue implementations
Goal:
• Implement a Queue class using a circular array
Before doing this lab make sure to read the class notes and review the class slides carefully.
• The implementation will use a circular array for storing the items in the queue. There are
different implementations but they share the idea presented in the picture. Namely
elements are added to the rear of the queue using the next “free entry” in an array. (rear
may be the index of the current last index storing an item in the queue or the index
beyond it Elements are removed from the front(read in the picture) of the queue.
Elements are added to the queue at the rear (write) of the queue. The indices in front and
rear are incremented as elements are added and deleted from the queue. All arithmetic is
modulo the size of the array structure allocated to store the queue. Care must be
taken in distinguishing a full queue from an empty queue and this can be done in different
ways. The specification below enables you do to this through the num_in_queue field.
Understand the implications of not having this field!
• Note that in some implementations that maximum number of items the queue can hold is
one less than the size of the array-like structure allocated. When a user of your Queue
class specifies its capacity, you may have to take this into account so that the queue can
actually store capacity items.
CPE 202 Fall 2017
January 17, 2022 Lab Week 3.docx 2
Use the following specification.
Make sure that each of your functions has a docstring that describes its purpose.
class Queue:
def __init__(self, capacity):
self.capacity = capacity
# the maximum number of items that can be stored in queue
self.num_in_queue = 0
# the number of items stored in queue
self.front = ??
self.rear = ???
def is_empty(self):
def is_full(self):
def enqueue(self, item):
def dequeue(self):
def num_in_queue(self):
“””returns the number of items in the queue”””
• The class Queue should raise an IndexError exception if a user of your implementation
attempts to enqueue an item when the queue is full or dequeue an item with the queue is
empty.
Submit the following two files to Canvas:
• queue_nodelist.py: Contains a linked based implementation of the Queue class
• queue_tests.py: Contains comprehensive tests to ensure your implementation of Queue
workscorrectly.

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