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

Challenge Notebook

Problem: Create a list for each level of a binary tree.

Constraints

  • Is this a binary search tree?
    • Yes
  • Should each level be a list of nodes?
    • Yes
  • Can we assume we already have a Node class with an insert method?
    • Yes
  • Can we assume this fits memory?
    • Yes

Test Cases

  • 5, 3, 8, 2, 4, 1, 7, 6, 9, 10, 11 -> [[5], [3, 8], [2, 4, 7, 9], [1, 6, 10], [11]]

Note: Each number in the result is actually a node containing the number

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 ../bst/bst.py
%load ../bst/bst.py
In [ ]:
class BstLevelLists(Bst):

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

Unit Test

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

In [ ]:
%run ../utils/results.py
In [ ]:
# %load test_tree_level_lists.py
import unittest


class TestTreeLevelLists(unittest.TestCase):

    def test_tree_level_lists(self):
        bst = BstLevelLists(Node(5))
        bst.insert(3)
        bst.insert(8)
        bst.insert(2)
        bst.insert(4)
        bst.insert(1)
        bst.insert(7)
        bst.insert(6)
        bst.insert(9)
        bst.insert(10)
        bst.insert(11)

        levels = bst.create_level_lists()
        results_list = []
        for level in levels:
            results = Results()
            for node in level:
                results.add_result(node)
            results_list.append(results)

        self.assertEqual(str(results_list[0]), '[5]')
        self.assertEqual(str(results_list[1]), '[3, 8]')
        self.assertEqual(str(results_list[2]), '[2, 4, 7, 9]')
        self.assertEqual(str(results_list[3]), '[1, 6, 10]')
        self.assertEqual(str(results_list[4]), '[11]')

        print('Success: test_tree_level_lists')


def main():
    test = TestTreeLevelLists()
    test.test_tree_level_lists()


if __name__ == '__main__':
    main()

Solution Notebook

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