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

Challenge Notebook

Problem: Delete a node in the middle, given only access to that node.

Constraints

  • Can we assume this is a non-circular, singly linked list?
    • Yes
  • What if the final node is being deleted, do we make it a dummy with value None?
    • Yes
  • Can we assume we already have a linked list class that can be used for this problem?
    • Yes

Test Cases

  • Delete on empty list -> None
  • Delete None -> None
  • Delete on one node -> [None]
  • Delete on multiple nodes

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 [ ]:
%run ../linked_list/linked_list.py
%load ../linked_list/linked_list.py
In [ ]:
class MyLinkedList(LinkedList):

    def delete_node(self, node):
        # TODO: Implement me
        pass

Unit Test

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

In [ ]:
# %load test_delete_mid.py
import unittest


class TestDeleteNode(unittest.TestCase):

    def test_delete_node(self):
        print('Test: Empty list, null node to delete')
        linked_list = MyLinkedList(None)
        linked_list.delete_node(None)
        self.assertEqual(linked_list.get_all_data(), [])

        print('Test: One node')
        head = Node(2)
        linked_list = MyLinkedList(head)
        linked_list.delete_node(head)
        self.assertEqual(linked_list.get_all_data(), [None])

        print('Test: Multiple nodes')
        linked_list = MyLinkedList(None)
        node0 = linked_list.insert_to_front(2)
        node1 = linked_list.insert_to_front(3)
        node2 = linked_list.insert_to_front(4)
        node3 = linked_list.insert_to_front(1)
        linked_list.delete_node(node1)
        self.assertEqual(linked_list.get_all_data(), [1, 4, 2])

        print('Test: Multiple nodes, delete last element')
        linked_list = MyLinkedList(None)
        node0 = linked_list.insert_to_front(2)
        node1 = linked_list.insert_to_front(3)
        node2 = linked_list.insert_to_front(4)
        node3 = linked_list.insert_to_front(1)
        linked_list.delete_node(node0)
        self.assertEqual(linked_list.get_all_data(), [1, 4, 3, None])

        print('Success: test_delete_node')


def main():
    test = TestDeleteNode()
    test.test_delete_node()


if __name__ == '__main__':
    main()

Solution Notebook

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