"""
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):
min_idx = i
for j in range(i + 1, n):
if collection[j] < collection[min_idx]:
min_idx = j
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))