From eb62b1433f300474b8f224bafd4a2f7c4d51da50 Mon Sep 17 00:00:00 2001
From: Rokeshwaran <rokeshwaran2008@gmail.com>
Date: Sun, 13 Sep 2026 12:40:37 +0530
Subject: [PATCH] sorts: make pancake_sort generic over Comparable items

Part of #15234

- switch pancake_sort's TypeVar to the Comparable/TypeVar-bound
  pattern used by insertion_sort.py
- add doctests covering strings, floats, and random data
- register pancake_sort in tests/test_sorts.py's shared battery and
  the non-comparable-items rejection test
---
 sorts/pancake_sort.py | 34 +++++++++++++++++++++++++++++-----
 tests/test_sorts.py   |  3 +++
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/sorts/pancake_sort.py b/sorts/pancake_sort.py
index 7fa4c02e981f..09c604f8c81f 100644
--- a/sorts/pancake_sort.py
+++ b/sorts/pancake_sort.py
@@ -1,5 +1,6 @@
 """
 This is a pure Python implementation of the pancake sort algorithm
+
 For doctests run following command:
 python3 -m doctest -v pancake_sort.py
 or
@@ -9,15 +10,23 @@
 """
 
 from collections.abc import Sequence
-from typing import TypeVar
+from typing import Any, Protocol, TypeVar
+
+
+class Comparable(Protocol):
+    def __lt__(self, other: Any, /) -> bool: ...
+
 
-T = TypeVar("T")
+T = TypeVar("T", bound=Comparable)
 
 
-def pancake_sort[T](arr: Sequence[T]) -> list[T]:
+def pancake_sort[T: Comparable](arr: Sequence[T]) -> list[T]:
     """Sort Array with Pancake Sort.
-    :param arr: Collection containing comparable items
-    :return: Collection ordered in ascending order of items
+
+    :param arr: some ordered collection with heterogeneous comparable items
+    inside
+    :return: the same collection ordered by ascending
+
     Examples:
     >>> pancake_sort([0, 5, 3, 2, 2])
     [0, 2, 2, 3, 5]
@@ -25,7 +34,18 @@ def pancake_sort[T](arr: Sequence[T]) -> list[T]:
     []
     >>> pancake_sort([-2, -5, -45])
     [-45, -5, -2]
+    >>> pancake_sort(['d', 'a', 'b', 'e', 'c']) == sorted(['d', 'a', 'b', 'e', 'c'])
+    True
+    >>> import random
+    >>> collection = random.sample(range(-50, 50), 100)
+    >>> pancake_sort(collection) == sorted(collection)
+    True
+    >>> import string
+    >>> collection = random.choices(string.ascii_letters + string.digits, k=100)
+    >>> pancake_sort(collection) == sorted(collection)
+    True
     """
+    arr = list(arr)
     cur = len(arr)
     while cur > 1:
         # Find the maximum number in arr
@@ -39,6 +59,10 @@ def pancake_sort[T](arr: Sequence[T]) -> list[T]:
 
 
 if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
+
     user_input = input("Enter numbers separated by a comma:\n").strip()
     unsorted = [int(item) for item in user_input.split(",")]
     print(pancake_sort(unsorted))
diff --git a/tests/test_sorts.py b/tests/test_sorts.py
index 2c9b79aa4bfe..2ac928737e78 100644
--- a/tests/test_sorts.py
+++ b/tests/test_sorts.py
@@ -33,6 +33,7 @@
 from sorts.iterative_merge_sort import iter_merge_sort
 from sorts.merge_sort import merge_sort
 from sorts.odd_even_sort import odd_even_sort
+from sorts.pancake_sort import pancake_sort
 from sorts.patience_sort import patience_sort
 from sorts.quick_sort import quick_sort
 from sorts.selection_sort import selection_sort
@@ -64,6 +65,7 @@ def test_heap_sort() -> None:
     iter_merge_sort,
     merge_sort,
     odd_even_sort,
+    pancake_sort,
     patience_sort,
     quick_sort,
     selection_sort,
@@ -121,6 +123,7 @@ def test_sort_matches_builtin(sort, case) -> None:
         gnome_sort,
         insertion_sort,
         merge_sort,
+        pancake_sort,
         selection_sort,
     ],
     ids=lambda f: f.__name__,