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 linked list with insert, append, find, delete, length, and print methods

Constraints
Test Cases
Algorithm
Code
Unit Test
Solution Notebook

Constraints

Is this a singly or doubly linked list?
- Singly
Is this a circular list?
- No
Do we keep track of the tail or just the head?
- Just the head

Test Cases

Insert to Front

Insert a None
Insert in an empty list
Insert in a list with one element or more elements

Append

Append a None
Append in an empty list
Insert in a list with one element or more elements

Find

Find a None
Find in an empty list
Find in a list with one element or more matching elements
Find in a list with no matches

Delete

Delete a None
Delete in an empty list
Delete in a list with one element or more matching elements
Delete in a list with no matches

Length

Length of zero or more elements

Print

Print an empty list
Print a list with one or more elements

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, next_node=None):
        pass
        # TODO: Implement me

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


class LinkedList(object):

    def __init__(self, head=None):
        pass
        # TODO: Implement me

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

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

    def append(self, data, next_node=None):
        pass
        # TODO: Implement me

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

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

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

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

Unit Test

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



In [ ]:

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


class TestLinkedList(object):

    def test_insert_to_front(self):
        print('Test: insert_to_front on an empty list')
        linked_list = LinkedList(None)
        linked_list.insert_to_front(10)
        assert_equal(linked_list.get_all_data(), [10])

        print('Test: insert_to_front on a None')
        linked_list.insert_to_front(None)
        assert_equal(linked_list.get_all_data(), [10])

        print('Test: insert_to_front general case')
        linked_list.insert_to_front('a')
        linked_list.insert_to_front('bc')
        assert_equal(linked_list.get_all_data(), ['bc', 'a', 10])

        print('Success: test_insert_to_front\n')

    def test_append(self):
        print('Test: append on an empty list')
        linked_list = LinkedList(None)
        linked_list.append(10)
        assert_equal(linked_list.get_all_data(), [10])

        print('Test: append a None')
        linked_list.append(None)
        assert_equal(linked_list.get_all_data(), [10])

        print('Test: append general case')
        linked_list.append('a')
        linked_list.append('bc')
        assert_equal(linked_list.get_all_data(), [10, 'a', 'bc'])

        print('Success: test_append\n')

    def test_find(self):
        print('Test: find on an empty list')
        linked_list = LinkedList(None)
        node = linked_list.find('a')
        assert_equal(node, None)

        print('Test: find a None')
        head = Node(10)
        linked_list = LinkedList(head)
        node = linked_list.find(None)
        assert_equal(node, None)

        print('Test: find general case with matches')
        head = Node(10)
        linked_list = LinkedList(head)
        linked_list.insert_to_front('a')
        linked_list.insert_to_front('bc')
        node = linked_list.find('a')
        assert_equal(str(node), 'a')

        print('Test: find general case with no matches')
        node = linked_list.find('aaa')
        assert_equal(node, None)

        print('Success: test_find\n')

    def test_delete(self):
        print('Test: delete on an empty list')
        linked_list = LinkedList(None)
        linked_list.delete('a')
        assert_equal(linked_list.get_all_data(), [])

        print('Test: delete a None')
        head = Node(10)
        linked_list = LinkedList(head)
        linked_list.delete(None)
        assert_equal(linked_list.get_all_data(), [10])

        print('Test: delete general case with matches')
        head = Node(10)
        linked_list = LinkedList(head)
        linked_list.insert_to_front('a')
        linked_list.insert_to_front('bc')
        linked_list.delete('a')
        assert_equal(linked_list.get_all_data(), ['bc', 10])

        print('Test: delete general case with no matches')
        linked_list.delete('aa')
        assert_equal(linked_list.get_all_data(), ['bc', 10])

        print('Success: test_delete\n')

    def test_len(self):
        print('Test: len on an empty list')
        linked_list = LinkedList(None)
        assert_equal(len(linked_list), 0)

        print('Test: len general case')
        head = Node(10)
        linked_list = LinkedList(head)
        linked_list.insert_to_front('a')
        linked_list.insert_to_front('bc')
        assert_equal(len(linked_list), 3)

        print('Success: test_len\n')


def main():
    test = TestLinkedList()
    test.test_insert_to_front()
    test.test_append()
    test.test_find()
    test.test_delete()
    test.test_len()


if __name__ == '__main__':
    main()

Solution Notebook

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