* Tighten up psf/black and flake8
* Fix some tests
* Fix some E741
* Fix some E741
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
* organized graph algorithms
* all graph algorithms in Graphs/ folder
* all graph algorithms are in one folder
* Rename number theory/factorial_python.py to maths/factorial_python.py