types(reverse_selection): constrain items to Comparable (#15410)

* types(reverse_selection): constrain items to Comparable

Bind reverse_selection_sort's element type to a Comparable Protocol so the
signature says "a list of items that can be compared with each other"
instead of a bare list, and keep the element type in the return.

reverse_subarray only swaps elements and never compares them, so its
TypeVar stays unbounded.

Also adds doctests for a comparable non-int type (strings, floats) and for
the failure mode: mixing non-comparable items must raise TypeError rather
than silently mis-sort. The test battery picks the sort up for the shared
cases and for the rejection check.

* updating DIRECTORY.md

---------

Co-authored-by: AuroraAeon <auroraeon@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>
Co-authored-by: cclauss <cclauss@users.noreply.github.com>

DIRECTORY.md

@@ -276,6 +276,7 @@
     * [Permutations](data_structures/arrays/permutations.py)
     * [Prefix Sum](data_structures/arrays/prefix_sum.py)
     * [Product Sum](data_structures/arrays/product_sum.py)
+    * [Reverse Array](data_structures/arrays/reverse_array.py)
     * [Rotate Array](data_structures/arrays/rotate_array.py)
     * [Set Matrix Zeroes](data_structures/arrays/set_matrix_zeroes.py)
     * [Sparse Table](data_structures/arrays/sparse_table.py)

sorts/reverse_selection.py

@@ -4,14 +4,20 @@ A pure Python implementation of the Reverse Selection Sort algorithm
 This algorithm progressively sorts the array by reversing subarrays
 
 For doctests run following command:
-python3 -m doctest -v reverse_selection_sort.py
+python3 -m doctest -v reverse_selection.py
 
 For manual testing run:
-python3 reverse_selection_sort.py
+python3 reverse_selection.py
 """
 
+from typing import Any, Protocol
 
-def reverse_subarray(arr: list, start: int, end: int) -> None:
+
+class Comparable(Protocol):
+    def __lt__(self, other: Any, /) -> bool: ...
+
+
+def reverse_subarray[T](arr: list[T], start: int, end: int) -> None:
     """
     Reverse a subarray in-place.
 
@@ -41,7 +47,7 @@ def reverse_subarray(arr: list, start: int, end: int) -> None:
         end -= 1
 
 
-def reverse_selection_sort(collection: list) -> list:
+def reverse_selection_sort[T: Comparable](collection: list[T]) -> list[T]:
     """
     A pure implementation of reverse selection sort algorithm in Python
 
@@ -64,6 +70,17 @@ def reverse_selection_sort(collection: list) -> list:
 
     >>> reverse_selection_sort([5, 4, 3, 2, 1])
     [1, 2, 3, 4, 5]
+
+    >>> reverse_selection_sort(["banana", "apple", "cherry"])
+    ['apple', 'banana', 'cherry']
+
+    >>> reverse_selection_sort([3.14, 1.5, 2.7])
+    [1.5, 2.7, 3.14]
+
+    >>> reverse_selection_sort([1, "a"])  # doctest: +ELLIPSIS
+    Traceback (most recent call last):
+    ...
+    TypeError: ...
     """
     n = len(collection)
     for i in range(n - 1):

tests/test_sorts.py

@@ -46,6 +46,7 @@ from sorts.quick_sort import quick_sort
 from sorts.quick_sort_3_partition import three_way_radix_quicksort
 from sorts.recursive_insertion_sort import rec_insertion_sort
 from sorts.recursive_mergesort_array import merge
+from sorts.reverse_selection import reverse_selection_sort
 from sorts.reversort import reversort
 from sorts.selection_sort import selection_sort
 from sorts.shell_sort import shell_sort
@@ -86,6 +87,7 @@ SORTS = (
     pancake_sort,
     patience_sort,
     quick_sort,
+    reverse_selection_sort,
     reversort,
     selection_sort,
     shell_sort,
@@ -163,6 +165,7 @@ def test_rec_insertion_sort(case) -> None:
         odd_even_transposition,
         pancake_sort,
         patience_sort,
+        reverse_selection_sort,
         reversort,
         selection_sort,
         shrink_shell_sort,