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

# Challenge Notebook¶

## Constraints¶

• What does it mean to invert a binary tree?
• Swap all left and right node pairs
• Can we assume we already have a Node class?
• Yes
• Can we assume the inputs are valid?
• No
• Can we assume this fits memory?
• Yes

## Test Cases¶

Input:
5
/   \
2     7
/ \   / \
1   3 6   9

Output:
5
/   \
7     2
/ \   / \
9   6 3   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

In [ ]:
class InverseBst(Bst):

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


## Unit Test¶

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

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

class TestInvertTree(unittest.TestCase):

def test_invert_tree(self):
root = Node(5)
bst = InverseBst(root)
node2 = bst.insert(2)
node3 = bst.insert(3)
node1 = bst.insert(1)
node7 = bst.insert(7)
node6 = bst.insert(6)
node9 = bst.insert(9)
result = bst.invert_tree()
self.assertEqual(result, root)
self.assertEqual(result.left, node7)
self.assertEqual(result.right, node2)
self.assertEqual(result.left.left, node9)
self.assertEqual(result.left.right, node6)
self.assertEqual(result.right.left, node3)
self.assertEqual(result.right.right, node1)
print('Success: test_invert_tree')

def main():
test = TestInvertTree()
test.test_invert_tree()

if __name__ == '__main__':
main()


## Solution Notebook¶

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