Optimization and fix bug (#2342)

* * optimization aliquot_sum
* fix bug in average_median

* fixup! Format Python code with psf/black push

* Update maths/average_median.py

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

data_structures/stacks/dijkstras_two_stack_algorithm.py

@@ -31,10 +31,10 @@ NOTE:   It only works with whole numbers.
 """
 __author__ = "Alexander Joslin"
 
-from .stack import Stack
-
 import operator as op
 
+from .stack import Stack
+
 
 def dijkstras_two_stack_algorithm(equation: str) -> int:
     """