interactive-coding-challenges/linked_lists/delete_mid/delete_mid_challenge.ipynb

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
• Test Cases
• Algorithm
• Code
• Unit Test
• Solution Notebook

Constraints

Problem statements are sometimes ambiguous. Identifying constraints and stating assumptions can help to ensure you code the intended solution.

• What if the final node is being deleted, for example a single node list? 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
from nose.tools import assert_equal


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

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

        print('Test: Multiple nodes')
        linked_list = MyLinkedList(None)        
        node0 = linked_list.insert_to_front(1)
        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(node2)
        assert_equal(linked_list.get_all_data(), [1, 3, 1])
        
        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.