This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

Challenge Notebook

Problem: Implement a queue with enqueue and dequeue methods using a linked list.

Constraints
Test Cases
Algorithm
Code
Unit Test
Pythonic-Code
Solution Notebook

Constraints

If there is one item in the list, do you expect the first and last pointers to both point to it?
- Yes
If there are no items on the list, do you expect the first and last pointers to be None?
- Yes
If you dequeue on an empty queue, does that return None?
- Yes

Test Cases

Enqueue

Enqueue to an empty queue
Enqueue to a non-empty queue

Dequeue

Dequeue an empty queue -> None
Dequeue a queue with one element
Dequeue a queue with more than one element

Algorithm

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

Code



In [ ]:

    
class Node(object):

    def __init__(self, data):
        # TODO: Implement me
        pass


class Queue(object):

    def __init__(self):
        # TODO: Implement me
        pass

    def enqueue(self, data):
        # TODO: Implement me
        pass

    def dequeue(self):
        # TODO: Implement me
        pass

Unit Test

The following unit test is expected to fail until you solve the challenge.



In [ ]:

    
# %load test_queue_list.py
from nose.tools import assert_equal


class TestQueue(object):

    # TODO: It would be better if we had unit tests for each
    # method in addition to the following end-to-end test
    def test_end_to_end(self):
        print('Test: Dequeue an empty queue')
        queue = Queue()
        assert_equal(queue.dequeue(), None)

        print('Test: Enqueue to an empty queue')
        queue.enqueue(1)

        print('Test: Dequeue a queue with one element')
        assert_equal(queue.dequeue(), 1)

        print('Test: Enqueue to a non-empty queue')
        queue.enqueue(2)
        queue.enqueue(3)
        queue.enqueue(4)

        print('Test: Dequeue a queue with more than one element')
        assert_equal(queue.dequeue(), 2)
        assert_equal(queue.dequeue(), 3)
        assert_equal(queue.dequeue(), 4)

        print('Success: test_end_to_end')


def main():
    test = TestQueue()
    test.test_end_to_end()


if __name__ == '__main__':
    main()

Solution Notebook

Review the Solution Notebook for a discussion on algorithms and code solutions.