Tighten up psf/black and flake8 (#2024)

* 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>

dynamic_programming/longest_common_subsequence.py

@@ -76,7 +76,7 @@ if __name__ == "__main__":
     expected_subseq = "GTAB"
 
     ln, subseq = longest_common_subsequence(a, b)
-    ##    print("len =", ln, ", sub-sequence =", subseq)
+    print("len =", ln, ", sub-sequence =", subseq)
     import doctest
 
     doctest.testmod()