Add type hints to pancake_sort function

Author: changsheng0804-blip

sorts/pancake_sort.py

@@ -8,8 +8,10 @@
 python pancake_sort.py
 """
 
+from typing import List
 
-def pancake_sort(arr):
+
+def pancake_sort(arr: List[int]) -> List[int]:
     """Sort Array with Pancake Sort.
     :param arr: Collection containing comparable items
     :return: Collection ordered in ascending order of items
@@ -36,4 +38,4 @@ def pancake_sort(arr):
 if __name__ == "__main__":
     user_input = input("Enter numbers separated by a comma:\n").strip()
     unsorted = [int(item) for item in user_input.split(",")]
-    print(pancake_sort(unsorted))
+    print(pancake_sort(unsorted))