* Tighten up psf/black and flake8
* Fix some tests
* Fix some E741
* Fix some E741
* updating DIRECTORY.md
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* Add Kth lexicographic permutation
Function that computes the kth lexicographic permtation of 0,1,2,...,n-1 in O(n^2) time
* Update kth_lexicographic_permutation.py
Addressed requested changes