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

Challenge Notebook

Problem: Implement depth-first traversals (in-order, pre-order, post-order) on a binary tree.

Constraints

  • Can we assume we already have a Node class with an insert method?
    • Yes
  • What should we do with each node when we process it?
    • Call an input method visit_func on the node
  • Can we assume this fits in memory?
    • Yes

Test Cases

In-Order Traversal

  • 5, 2, 8, 1, 3 -> 1, 2, 3, 5, 8
  • 1, 2, 3, 4, 5 -> 1, 2, 3, 4, 5

Pre-Order Traversal

  • 5, 2, 8, 1, 3 -> 5, 2, 1, 3, 8
  • 1, 2, 3, 4, 5 -> 1, 2, 3, 4, 5

Post-Order Traversal

  • 5, 2, 8, 1, 3 -> 1, 3, 2, 8, 5
  • 1, 2, 3, 4, 5 -> 5, 4, 3, 2, 1

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 BstDfs(Bst):

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

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

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

Unit Test

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


class TestDfs(unittest.TestCase):

    def __init__(self, *args, **kwargs):
        super(TestDfs, self).__init__()
        self.results = Results()

    def test_dfs(self):
        bst = BstDfs(Node(5))
        bst.insert(2)
        bst.insert(8)
        bst.insert(1)
        bst.insert(3)

        bst.in_order_traversal(bst.root, self.results.add_result)
        self.assertEqual(str(self.results), "[1, 2, 3, 5, 8]")
        self.results.clear_results()

        bst.pre_order_traversal(bst.root, self.results.add_result)
        self.assertEqual(str(self.results), "[5, 2, 1, 3, 8]")
        self.results.clear_results()

        bst.post_order_traversal(bst.root, self.results.add_result)
        self.assertEqual(str(self.results), "[1, 3, 2, 8, 5]")
        self.results.clear_results()

        bst = BstDfs(Node(1))
        bst.insert(2)
        bst.insert(3)
        bst.insert(4)
        bst.insert(5)

        bst.in_order_traversal(bst.root, self.results.add_result)
        self.assertEqual(str(self.results), "[1, 2, 3, 4, 5]")
        self.results.clear_results()

        bst.pre_order_traversal(bst.root, self.results.add_result)
        self.assertEqual(str(self.results), "[1, 2, 3, 4, 5]")
        self.results.clear_results()

        bst.post_order_traversal(bst.root, self.results.add_result)
        self.assertEqual(str(self.results), "[5, 4, 3, 2, 1]")

        print('Success: test_dfs')


def main():
    test = TestDfs()
    test.test_dfs()


if __name__ == '__main__':
    main()

Solution Notebook

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