Add Shell Sort Algorithm

sorts/shell_sort.py

@@ -4,10 +4,11 @@
 
 
 def shell_sort(collection: list[int]) -> list[int]:
-    """Pure implementation of shell sort algorithm in Python
-    :param collection:  Some mutable ordered collection with heterogeneous
-    comparable items inside
-    :return:  the same collection ordered by ascending
+    """
+    Sort a list of integers using the Shell Sort algorithm.
+
+    Reference:
+    https://en.wikipedia.org/wiki/Shellsort
 
     >>> shell_sort([0, 5, 3, 2, 2])
     [0, 2, 2, 3, 5]
@@ -16,25 +17,15 @@ def shell_sort(collection: list[int]) -> list[int]:
     >>> shell_sort([-2, -5, -45])
     [-45, -5, -2]
     """
-    # Marcin Ciura's gap sequence
-
     gaps = [701, 301, 132, 57, 23, 10, 4, 1]
+
     for gap in gaps:
         for i in range(gap, len(collection)):
             insert_value = collection[i]
             j = i
             while j >= gap and collection[j - gap] > insert_value:
                 collection[j] = collection[j - gap]
                 j -= gap
-            if j != i:
-                collection[j] = insert_value
-    return collection
-
+            collection[j] = insert_value
 
-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(shell_sort(unsorted))
+    return collection