aoc2021-21.py

import collections
import functools
import itertools

POSITIONS = (9, 6)

DICE = [1, 2, 3]
SUMS = collections.defaultdict(int)
for a, b, c in itertools.product(DICE, DICE, DICE):
    SUMS[a + b + c] += 1


def part1(position):
    die = itertools.cycle(range(1, 101))
    position = list(position)
    points = [0, 0]
    rolls = 0
    turn = 0

    while all(p < 1000 for p in points):
        a, b, c = next(die), next(die), next(die)
        rolls += 3
        position[turn] = (position[turn] + a + b + c - 1) % 10 + 1
        points[turn] += position[turn]
        turn = 1 - turn

    return min(points) * rolls


@functools.lru_cache(maxsize=None)
def part2(positions, points=(0, 0), turn=0):

    if points[0] >= 21:
        return 1, 0

    if points[1] >= 21:
        return 0, 1

    ret = 0, 0

    new_positions = list(positions)
    new_points = list(points)

    for move, count in SUMS.items():

        new_positions[turn] = (positions[turn] + move - 1) % 10 + 1
        new_points[turn] = points[turn] + new_positions[turn]

        wins = part2(tuple(new_positions), tuple(new_points), 1 - turn)

        ret = ret[0] + wins[0] * count, ret[1] + wins[1] * count

    return ret


print("Part 1: ", part1(POSITIONS))
print("Part 2: ", max(part2(POSITIONS)))