Python/sorts/bucket_sort.py

#!/usr/bin/env python3
"""
Illustrate how to implement bucket sort algorithm.

Author: OMKAR PATHAK
This program will illustrate how to implement bucket sort algorithm

Wikipedia says: Bucket sort, or bin sort, is a sorting algorithm that works
by distributing the elements of an array into a number of buckets.
Each bucket is then sorted individually, either using a different sorting
algorithm, or by recursively applying the bucket sorting algorithm. It is a
distribution sort, and is a cousin of radix sort in the most to least
significant digit flavour.
Bucket sort is a generalization of pigeonhole sort. Bucket sort can be
implemented with comparisons and therefore can also be considered a
comparison sort algorithm. The computational complexity estimates involve the
number of buckets.

Time Complexity of Solution:
Worst case scenario occurs when all the elements are placed in a single bucket.
The overall performance would then be dominated by the algorithm used to sort each
bucket. In this case, O(n log n), because of TimSort

Average Case O(n + (n^2)/k + k), where k is the number of buckets

If k = O(n), time complexity is O(n)

Source: https://en.wikipedia.org/wiki/Bucket_sort
"""
DEFAULT_BUCKET_SIZE = 5


def bucket_sort(my_list: list, bucket_size: int = DEFAULT_BUCKET_SIZE) -> list:
    """
    >>> data = [-1, 2, -5, 0]
    >>> bucket_sort(data) == sorted(data)
    True

    >>> data = [9, 8, 7, 6, -12]
    >>> bucket_sort(data) == sorted(data)
    True

    >>> data = [.4, 1.2, .1, .2, -.9]
    >>> bucket_sort(data) == sorted(data)
    True

    >>> bucket_sort([])
    Traceback (most recent call last):
      ...
    Exception: Please add some elements in the array.
    """
    if len(my_list) == 0:
        raise Exception("Please add some elements in the array.")

    min_value, max_value = (min(my_list), max(my_list))
    bucket_count = (max_value - min_value) // bucket_size + 1
    buckets = [[] for _ in range(int(bucket_count))]

    for i in range(len(my_list)):
        buckets[int((my_list[i] - min_value) // bucket_size)].append(my_list[i])

    return sorted(
        buckets[i][j] for i in range(len(buckets)) for j in range(len(buckets[i]))
    )


if __name__ == "__main__":
    assert bucket_sort([4, 5, 3, 2, 1]) == [1, 2, 3, 4, 5]
    assert bucket_sort([0, 1, -10, 15, 2, -2]) == [-10, -2, 0, 1, 2, 15]