adjust quicksort comments, add todo for quickselect

Author: jshields

academic/examples/search/quickselect.py

@@ -0,0 +1,34 @@
+"""
+TODO
+quickselect algorithm
+find k-th smallest item in an unordered list
+
+Works by separating smaller items onto one side of the pivot,
+not caring about the particular order but about the number of smaller items on that side.
+For example, with k of 5,
+the 5th smallest item will have 4 items smaller than it partitioned to its left.
+
+https://stackoverflow.com/questions/10846482/quickselect-algorithm-understanding
+
+to read
+http://www.cs.yale.edu/homes/aspnes/pinewiki/QuickSelect.html
+https://www.techiedelight.com/quickselect-algorithm/
+
+
+
+https://www.geeksforgeeks.org/quickselect-algorithm/
+https://www.geeksforgeeks.org/quick-sort/
+
+https://en.wikipedia.org/wiki/Quickselect
+https://en.wikipedia.org/wiki/Quicksort
+
+
+
+in theory, quick sort partition method should be the same for quick select
+can they share a method?
+
+"""
+
+
+def quick_select():
+    pass

academic/examples/sort/quick.py

@@ -166,7 +166,7 @@ def _quick(cls, lst, left, right):
         logging.debug('left: {left}, right: {right}'.format(left=left, right=right))
 
         pivot_index = (left + right) // 2
-        # possibly should/could be this?
+        # Could be this to prevent integer overflow:
         # pivot_index = left + (right-left) // 2
 
         logging.debug('pivot index: {ind}'.format(ind=pivot_index))
@@ -213,7 +213,8 @@ def _quick(cls, lst, left, right):
             )
         )
 
-        # may be needed for larger lists:
+        # May need iterative approach for larger lists due to recursion limit
+        # Recursion limit can be increased but not ideal for stack size/speed:
         # sys.setrecursionlimit(sys.getrecursionlimit() * 10)
 
         cls._quick(lst, left_init, right)