Advent of Code - day 21 in Python 3

day21.py

#!/usr/bin/env python3

import math
import itertools

class Stats(object):
    def __init__(self, hp, damage, armor):
        self.hit_points = hp
        self.damage = damage
        self.armor = armor

class Item(object):
    def __init__(self, cost, damage, armor):
        self.cost = cost
        self.damage = damage
        self.armor = armor
    def __repr__(self):
        return 'Item({}, {}, {})'.format(self.cost, self.damage, self.armor)

WEAPONS = [
    Item( 8, 4, 0),
    Item(10, 5, 0),
    Item(25, 6, 0),
    Item(40, 7, 0),
    Item(74, 8, 0),
]

ARMOR = [
    Item( 13, 0, 1),
    Item( 31, 0, 2),
    Item( 53, 0, 3),
    Item( 75, 0, 4),
    Item(102, 0, 5),
];

RINGS = [
    Item( 25, 1, 0),
    Item( 50, 2, 0),
    Item(100, 3, 0),
    Item( 20, 0, 1),
    Item( 40, 0, 2),
    Item( 80, 0, 3),
];

def choose_items(items, at_least, at_most=None):
    if at_most is None:
        at_most = len(items)

    for i in range(at_least, at_most+1):
        yield from itertools.combinations(items, i)

def does_player_win(player, boss):
    player_damage = max(player.damage - boss.armor, 1)
    player_wins_at = math.ceil(boss.hit_points / player_damage)

    boss_damage = max(boss.damage - player.armor, 1)
    boss_wins_at = math.ceil(player.hit_points / boss_damage)

    return player_wins_at <= boss_wins_at

def main():
    input_fname = 'day21_input.txt'
    with open(input_fname) as f:
        boss_hitpoints = int(f.readline().split(': ')[1])
        boss_damage = int(f.readline().split(': ')[1])
        boss_armor = int(f.readline().split(': ')[1])

    boss = Stats(boss_hitpoints, boss_damage, boss_armor)
    player_hitpoints = 100

    min_cost = None

    for weapons in choose_items(WEAPONS, 1, 1):
        for armors in choose_items(ARMOR, 0, 1):
            for rings in choose_items(RINGS, 0, 2):
                damage = 0
                armor = 0
                cost = 0
                for item in itertools.chain(weapons, armors, rings):
                    damage += item.damage
                    armor += item.armor
                    cost += item.cost

                    if does_player_win(
                            Stats(player_hitpoints, damage, armor),
                            boss):
                        if min_cost is None or cost < min_cost:
                            min_cost = cost
    print('Min cost:', min_cost)


    max_cost = None

    for weapons in choose_items(WEAPONS, 1):
        for armors in choose_items(ARMOR, 0):
            for rings in choose_items(RINGS, 0):
                damage = 0
                armor = 0
                cost = 0
                for item in itertools.chain(weapons, armors, rings):
                    damage += item.damage
                    armor += item.armor
                    cost += item.cost

                    if not does_player_win(
                            Stats(player_hitpoints, damage, armor),
                            boss):
                        if max_cost is None or cost > max_cost:
                            max_cost = cost
    print('Max cost to lose:', max_cost)

if __name__ == '__main__':
    main()