This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

Challenge Notebook

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

Constraints
Test Cases
Algorithm
Code
Unit Test

Constraints

Can we assume we already have a Node class with an insert method?
- 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 [ ]:

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

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

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

Unit Test



In [ ]:

    
%run ../utils/results.py



In [ ]:

    
# %load test_dfs.py
from nose.tools import assert_equal


class TestDfs(object):

    def __init__(self):
        self.results = Results()

    def test_dfs(self):
        node = Node(5)
        insert(node, 2)
        insert(node, 8)
        insert(node, 1)
        insert(node, 3)

        in_order_traversal(node, self.results.add_result)
        assert_equal(str(self.results), "[1, 2, 3, 5, 8]")
        self.results.clear_results()

        pre_order_traversal(node, self.results.add_result)
        assert_equal(str(self.results), "[5, 2, 1, 3, 8]")
        self.results.clear_results()

        post_order_traversal(node, self.results.add_result)
        assert_equal(str(self.results), "[1, 3, 2, 8, 5]")
        self.results.clear_results()

        node = Node(1)
        insert(node, 2)
        insert(node, 3)
        insert(node, 4)
        insert(node, 5)

        in_order_traversal(node, self.results.add_result)
        assert_equal(str(self.results), "[1, 2, 3, 4, 5]")
        self.results.clear_results()

        pre_order_traversal(node, self.results.add_result)
        assert_equal(str(self.results), "[1, 2, 3, 4, 5]")
        self.results.clear_results()

        post_order_traversal(node, self.results.add_result)
        assert_equal(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.