Added reverse_selection.py

sorts/reverse_selection.py

@@ -0,0 +1,87 @@
+"""
+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
+
+For manual testing run:
+python3 reverse_selection_sort.py
+"""
+
+
+def reverse_subarray(arr: list, start: int, end: int) -> None:
+    """
+    Reverse a subarray in-place.
+
+    :param arr: the array containing the subarray to be reversed
+    :param start: the starting index of the subarray
+    :param end: the ending index of the subarray
+
+    Examples:
+    >>> lst = [1, 2, 3, 4, 5]
+    >>> reverse_subarray(lst, 1, 3)
+    >>> lst
+    [1, 4, 3, 2, 5]
+
+    >>> lst = [1]
+    >>> reverse_subarray(lst, 0, 0)
+    >>> lst
+    [1]
+
+    >>> lst = [1, 2]
+    >>> reverse_subarray(lst, 0, 1)
+    >>> lst
+    [2, 1]
+    """
+    while start < end:
+        arr[start], arr[end] = arr[end], arr[start]
+        start += 1
+        end -= 1
+
+
+def reverse_selection_sort(collection: list) -> list:
+    """
+    A pure implementation of reverse selection sort algorithm in Python
+
+    :param collection: some mutable ordered collection with heterogeneous
+    comparable items inside
+    :return: the same collection sorted in ascending order
+
+    Examples:
+    >>> reverse_selection_sort([1, 9, 5, 21, 17, 6])
+    [1, 5, 6, 9, 17, 21]
+
+    >>> reverse_selection_sort([])
+    []
+
+    >>> reverse_selection_sort([-3, -17, -48])
+    [-48, -17, -3]
+
+    >>> reverse_selection_sort([1, 1, 1, 1])
+    [1, 1, 1, 1]
+
+    >>> reverse_selection_sort([5, 4, 3, 2, 1])
+    [1, 2, 3, 4, 5]
+    """
+    n = len(collection)
+    for i in range(n - 1):
+        # Find the minimum element in the unsorted portion
+        min_idx = i
+        for j in range(i + 1, n):
+            if collection[j] < collection[min_idx]:
+                min_idx = j
+
+        # If the minimum is not at the start of the unsorted portion,
+        # reverse the subarray to bring it to the front
+        if min_idx != i:
+            reverse_subarray(collection, i, min_idx)
+
+    return collection
+
+
+if __name__ == "__main__":
+    user_input = input("Enter numbers separated by a comma:\n").strip()
+    unsorted = [int(item) for item in user_input.split(",")]
+    print(reverse_selection_sort(unsorted))