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

Challenge Notebook¶

Problem: Find all permutations of an input string.¶

Constraints¶

Can the input have duplicates?
- Yes
Can the output have duplicates?
- No
Is the output a list of strings?
- Yes
Do we have to output the results in sorted order?
- No
Can we assume the inputs are valid?
- No
Can we assume this fits memory?
- Yes

Test Cases¶

* None -> None
* '' -> ''
* 'AABC' -> ['AABC', 'AACB', 'ABAC', 'ABCA',
             'ACAB', 'ACBA', 'BAAC', 'BACA',
             'BCAA', 'CAAB', 'CABA', 'CBAA']

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 find_permutations(self, string):
        # TODO: Implement me
        pass

Unit Test¶

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

In [ ]:

# %load test_permutations.py
import unittest


class TestPermutations(unittest.TestCase):

    def test_permutations(self):
        permutations = Permutations()
        self.assertEqual(permutations.find_permutations(None), None)
        self.assertEqual(permutations.find_permutations(''), '')
        string = 'AABC'
        expected = [
            'AABC', 'AACB', 'ABAC', 'ABCA',
            'ACAB', 'ACBA', 'BAAC', 'BACA',
            'BCAA', 'CAAB', 'CABA', 'CBAA'
        ]
        self.assertEqual(permutations.find_permutations(string), expected)
        print('Success: test_permutations')


def main():
    test = TestPermutations()
    test.test_permutations()


if __name__ == '__main__':
    main()

Solution Notebook¶

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