* calculates the number of permutations and combinations
* calculates the number of permutations and combinations
* calculates the number of permutations and combinations
* updating DIRECTORY.md
* calculates the number of permutations and combinations
* calculates the number of permutations and combinations
* fixed a typo
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>