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

Challenge Notebook

Problem: Determine if a string is a permutation of another string.

Constraints

  • Can we assume the string is ASCII?
    • Yes
    • Note: Unicode strings could require special handling depending on your language
  • Is whitespace important?
    • Yes
  • Is this case sensitive? 'Nib', 'bin' is not a match?
    • Yes
  • Can we use additional data structures?
    • Yes
  • Can we assume this fits in memory?
    • Yes

Test Cases

  • One or more None inputs -> False
  • One or more empty strings -> False
  • 'Nib', 'bin' -> False
  • 'act', 'cat' -> True
  • 'a ct', 'ca t' -> True

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 Permutations(object):

    def is_permutation(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_permutation_solution.py
import unittest


class TestPermutation(unittest.TestCase):

    def test_permutation(self, func):
        self.assertEqual(func(None, 'foo'), False)
        self.assertEqual(func('', 'foo'), False)
        self.assertEqual(func('Nib', 'bin'), False)
        self.assertEqual(func('act', 'cat'), True)
        self.assertEqual(func('a ct', 'ca t'), True)
        self.assertEqual(func('dog', 'doggo'), False)
        print('Success: test_permutation')


def main():
    test = TestPermutation()
    permutations = Permutations()
    test.test_permutation(permutations.is_permutation)
    try:
        permutations_alt = PermutationsAlt()
        test.test_permutation(permutations_alt.is_permutation)
    except NameError:
        # Alternate solutions are only defined
        # in the solutions file
        pass


if __name__ == '__main__':
    main()

Solution Notebook

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