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

Challenge Notebook

Problem: Check if a binary tree is balanced.

Constraints

  • Is a balanced tree one where the heights of two sub trees of any node doesn't differ by more than 1?
    • Yes
  • If this is called on a None input, should we raise an exception?
    • Yes
  • Can we assume we already have a Node class with an insert method?
    • Yes
  • Can we assume this fits memory?
    • Yes

Test Cases

  • None -> No
  • 1 -> Yes
  • 5, 3, 8, 1, 4 -> Yes
  • 5, 3, 8, 9, 10 -> No

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 BstBalance(Bst):

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

Unit Test

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

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


class TestCheckBalance(unittest.TestCase):

    def test_check_balance_empty(self):
        bst = BstBalance(None)
        bst.check_balance()

    def test_check_balance(self):
        bst = BstBalance(Node(5))
        self.assertEqual(bst.check_balance(), True)

        bst.insert(3)
        bst.insert(8)
        bst.insert(1)
        bst.insert(4)
        self.assertEqual(bst.check_balance(), True)

        bst = BstBalance(Node(5))
        bst.insert(3)
        bst.insert(8)
        bst.insert(9)
        bst.insert(10)
        self.assertEqual(bst.check_balance(), False)

        bst = BstBalance(Node(3))
        bst.insert(2)
        bst.insert(1)
        bst.insert(5)
        bst.insert(4)
        bst.insert(6)
        bst.insert(7)
        self.assertEqual(bst.check_balance(), True)

        print('Success: test_check_balance')


def main():
    test = TestCheckBalance()
    test.assertRaises(TypeError, test.test_check_balance_empty)
    test.test_check_balance()


if __name__ == '__main__':
    main()

Solution Notebook

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