def solution(num_buns, num_required):
    duplication_factor = num_buns - num_required + 1
    result = [[] for bun in range(num_buns)]
    key_id = 0
    for dist in generate_key_distribution(num_buns, duplication_factor):
        for bun in range(num_buns):
            if dist[bun]:
                result[bun] += [key_id]
        key_id += 1
    return result

def generate_key_distribution(num_buns, duplication):
    if num_buns == duplication:
        yield [True for i in range(num_buns)]
    elif num_buns > 0:
        if duplication > 0:
            for dist in generate_key_distribution(num_buns - 1, duplication - 1):
                yield [True] + dist
        for dist in generate_key_distribution(num_buns - 1, duplication):
            yield [False] + dist


tests = [
        ((3, 1), [[0], [0], [0]]),
        ((2, 2), [[0], [1]]),
        ((3, 2), [[0, 1], [0, 2], [1, 2]]),
        ((2, 1), [[0], [0]]),
        ((4, 4), [[0], [1], [2], [3]]),
        ((5, 3), [[0, 1, 2, 3, 4, 5], [0, 1, 2, 6, 7, 8], [0, 3, 4, 6, 7, 9], [1, 3, 5, 6, 8, 9], [2, 4, 5, 7, 8, 9]])
        ]

for i, o in tests:
    result = solution(*i)
    print(i, result == o, result, o)