from itertools import islice

factor_a, factor_b = 16807, 48271


def generator(start, factor, mod=1):
    value = start
    while True:
        value *= factor
        value %= 2147483647
        if value % mod == 0:
            yield value


def count_matches(gen_a, gen_b, limit=4 * 10**7):
    return sum(
        1 for a, b in islice(zip(gen_a, gen_b), limit) if a & 0xFFFF == b & 0xFFFF
    )

test_gen_a, test_gen_b = generator(65, factor_a), generator(8921, factor_b)
tests = [
    (1092455, 430625591),
    (1181022009, 1233683848),
    (245556042, 1431495498),
    (1744312007, 137874439),
    (1352636452, 285222916),
]
for expected_a, expected_b in tests:
    assert (next(test_gen_a), next(test_gen_b)) == (expected_a, expected_b)

tests = [
    (1352636452, 1233683848),
    (1992081072, 862516352),
    (530830436, 1159784568),
    (1980017072, 1616057672),
    (740335192, 412269392),
]
test_gen_a, test_gen_b = generator(65, factor_a, 4), generator(8921, factor_b, 8)
for expected_a, expected_b in tests:
    assert (next(test_gen_a), next(test_gen_b)) == (expected_a, expected_b)

test_gen_a, test_gen_b = generator(65, factor_a), generator(8921, factor_b)
assert count_matches(test_gen_a, test_gen_b) == 588

test_gen_a, test_gen_b = generator(65, factor_a, 4), generator(8921, factor_b, 8)
assert count_matches(test_gen_a, test_gen_b, 5 * 10**6) == 309

import aocd

data = aocd.get_data(day=15, year=2017)
start_a, start_b = (int(line.rpartition(" ")[-1]) for line in data.splitlines())