iterative_combinations.py

# N. P. O'Donnell, 2024

from typing import Iterator


def generate_combinations(elements: list[any], count: int) -> Iterator[list[int]]:
    """
    Non-recursive generation of combinations.

    :param elements: Elements from which to make combinations.
    :param count: Size of each combination.
    :return: Each combination.
    """
    indexes = [i for i in range(count)]

    while indexes and indexes[-1] != len(elements):
        a = [elements[i] for i in indexes]
        ei = -1

        while indexes[0] != len(elements) - count + 1:
            indexes[ei] += 1
            for fi in range(ei + 1, 0):
                indexes[fi] = indexes[fi - 1] + 1
            if indexes[ei] > len(elements) + ei:
                ei -= 1
            else:
                break
        yield a


def main():
    for c in generate_combinations(['a', 'b', 'c', 'd', 'e', 'f'], 4):
        print(c)


if __name__ == "__main__":
    main()