aoc/2021/21_dice.py

#!/usr/bin/env python3
import sys
from itertools import cycle, product
from functools import lru_cache

def move(pos, score, amount):
    pos = (pos + amount - 1) % 10 + 1
    return pos, score + pos

def practice(a, b):
    players = [(a, 0), (b, 0)]
    die = cycle(range(1, 101))
    rolls = 0
    while True:
        for player, (pos, score) in enumerate(players):
            roll = next(die) + next(die) + next(die)
            rolls += 3
            pos, score = players[player] = move(pos, score, roll)
            if score >= 1000:
                otherpos, otherscore = players[1 - player]
                return rolls * otherscore

def play(a, b):
    @lru_cache(maxsize=None)
    def wins(a, b):
        awins = bwins = 0
        for rolls in product(range(1, 4), repeat=3):
            pos, score = roll_a = move(*a, sum(rolls))
            if score >= 21:
                awins += 1
            else:
                roll_bwins, roll_awins = wins(b, roll_a)
                awins += roll_awins
                bwins += roll_bwins
        return awins, bwins
    return max(wins((a, 0), (b, 0)))

a, b = (int(line.split(': ')[-1]) for line in sys.stdin)
print(practice(a, b))
print(play(a, b))