Created
March 28, 2023 03:26
-
-
Save hartwork/ad509aaa526bc2eb6de95c82c30817a0 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| # Demo of finding the nth permutation of a list in-place in Python >=3.8 | |
| # Copyright (c) 2023 Sebastian Pipping <sebastian@pipping.org> | |
| # SPDX-License-Identifier: GPL-3.0-or-later | |
| from copy import copy | |
| from math import factorial | |
| from typing import List | |
| from unittest import TestCase, TestLoader, TextTestRunner | |
| def permute_inplace(permutation: int, values: List): | |
| for target_index in range(len(values)): | |
| choices_count = len(values) - target_index | |
| source_index = permutation % choices_count + target_index | |
| if source_index != target_index: | |
| # Swap | |
| values[target_index], values[source_index] = ( | |
| values[source_index], | |
| values[target_index], | |
| ) | |
| permutation //= choices_count | |
| class PermuteTest(TestCase): | |
| original = list(range(6)) | |
| permutations_count = factorial(len(original)) | |
| def test_no_overlaps(self): | |
| permutations = set() | |
| for i in range(self.permutations_count): | |
| clone = copy(self.original) | |
| permute_inplace(i, clone) | |
| permutations.add(str(clone)) | |
| self.assertEqual(len(permutations), self.permutations_count) | |
| def test_ring_property(self): | |
| for i in range(self.permutations_count): | |
| clone_a = copy(self.original) | |
| clone_b = copy(self.original) | |
| permute_inplace(0 - i, clone_a) | |
| permute_inplace(self.permutations_count - i, clone_b) | |
| self.assertEqual(clone_b, clone_a) | |
| if __name__ == "__main__": | |
| test_suite = TestLoader().loadTestsFromTestCase(PermuteTest) | |
| TextTestRunner(verbosity=2).run(test_suite) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment