This notebook was prepared by Donne Martin. Source and license info is on GitHub.

Challenge Notebook

Problem: Implement a linked list with insert, append, find, delete, length, and print methods.

Constraints

  • Can we assume this is a non-circular, singly linked list?
    • Yes
  • Do we keep track of the tail or just the head?
    • Just the head
  • Can we insert None values?
    • No

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):
        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
import unittest


class TestLinkedList(unittest.TestCase):

    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)
        self.assertEqual(linked_list.get_all_data(), [10])

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

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

        print('Test: append general case')
        linked_list.append('a')
        linked_list.append('bc')
        self.assertEqual(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')
        self.assertEqual(node, None)

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

        print('Test: find general case with no matches')
        node = linked_list.find('aaa')
        self.assertEqual(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')
        self.assertEqual(linked_list.get_all_data(), [])

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

        print('Test: delete general case with no matches')
        linked_list.delete('aa')
        self.assertEqual(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)
        self.assertEqual(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')
        self.assertEqual(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.