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

Challenge Notebook¶

Constraints¶

• Can we assume the strings are ASCII?
• Yes
• Is case important?
• The strings are lower case
• Can we assume the inputs are valid?
• No, check for None
• Otherwise, assume there is only a single different char between the two strings
• Can we assume this fits memory?
• Yes

Test Cases¶

• None input -> TypeError
• 'ab', 'aab' -> 'a'
• 'aab', 'ab' -> 'a'
• 'abcd', 'abcde' -> 'e'

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 [ ]:
class Solution(object):

def find_diff(self, str1, str2):
# TODO: Implement me
pass


Unit Test¶

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

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

class TestFindDiff(unittest.TestCase):

def test_find_diff(self):
solution = Solution()
self.assertRaises(TypeError, solution.find_diff, None)
self.assertEqual(solution.find_diff('ab', 'aab'), 'a')
self.assertEqual(solution.find_diff('aab', 'ab'), 'a')
self.assertEqual(solution.find_diff('abcd', 'abcde'), 'e')
self.assertEqual(solution.find_diff_xor('ab', 'aab'), 'a')
self.assertEqual(solution.find_diff_xor('aab', 'ab'), 'a')
self.assertEqual(solution.find_diff_xor('abcd', 'abcde'), 'e')
print('Success: test_find_diff')

def main():
test = TestFindDiff()
test.test_find_diff()

if __name__ == '__main__':
main()


Solution Notebook¶

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