# -*- encoding: utf-8 -*- import copy import sys from functools import reduce from typing import Callable class Monkey: id: int items: list[int] worry_fn: Callable[[int], int] test_value: int throw_targets: dict[bool, int] def __init__( self, id: int, items: list[int], worry_fn: Callable[[int], int], test_value: int, throw_targets: dict[bool, int], ): self.id = id self.items = items self.worry_fn = worry_fn self.test_value = test_value self.throw_targets = throw_targets def __eq__(self, o: object) -> bool: if not isinstance(o, Monkey): return False return self.id == o.id def __hash__(self) -> int: return hash(self.id) def parse_monkey(lines: list[str]) -> Monkey: assert lines[0].startswith("Monkey") monkey_id = int(lines[0].split()[-1][:-1]) # parse items items = [int(r.strip()) for r in lines[1].split(":")[1].split(",")] # parse worry worry_fn: Callable[[int], int] worry_s = lines[2].split("new =")[1].strip() operand = worry_s.split()[-1].strip() if worry_s.startswith("old *"): if operand == "old": def worry_fn(w: int) -> int: return w * w else: def worry_fn(w: int) -> int: return w * int(operand) elif worry_s.startswith("old +"): if operand == "old": def worry_fn(w: int) -> int: return w + w else: def worry_fn(w: int) -> int: return w + int(operand) else: assert False, worry_s # parse test assert lines[3].split(":")[1].strip().startswith("divisible by") test_value = int(lines[3].split()[-1]) assert lines[4].strip().startswith("If true") assert lines[5].strip().startswith("If false") throw_targets = {True: int(lines[4].split()[-1]), False: int(lines[5].split()[-1])} assert monkey_id not in throw_targets.values() return Monkey(monkey_id, items, worry_fn, test_value, throw_targets) def run( monkeys: list[Monkey], n_rounds: int, me_worry_fn: Callable[[int], int] ) -> dict[Monkey, int]: """ The list of monkeys is modified in place. Args: monkeys: Initial list of monkeys. The Monkey will be modified in places (their items attributes). n_rounds: Number of rounds to run. me_worry_fn: Worry function to apply after the Monkey operation (e.g., divide by 3 for round 1). Returns: A mapping containing, for each monkey, the number of items inspected. """ inspects = {monkey: 0 for monkey in monkeys} for round in range(n_rounds): for monkey in monkeys: for item in monkey.items: inspects[monkey] += 1 # compute the new worry level item = me_worry_fn(monkey.worry_fn(item)) # find the target target = monkey.throw_targets[item % monkey.test_value == 0] assert target != monkey.id monkeys[target].items.append(item) # clear after the loop monkey.items.clear() return inspects def monkey_business(inspects: dict[Monkey, int]) -> int: sorted_levels = sorted(inspects.values()) return sorted_levels[-2] * sorted_levels[-1] monkeys = [parse_monkey(block.splitlines()) for block in sys.stdin.read().split("\n\n")] # case 1: we simply divide the worry by 3 after applying the monkey worry operation answer_1 = monkey_business( run(copy.deepcopy(monkeys), 20, me_worry_fn=lambda w: w // 3) ) print(f"answer 1 is {answer_1}") # case 2: to keep reasonable level values, we can use a modulo operation, we need to # use the product of all "divisible by" test so that the test remains valid # # (a + b) % c == ((a % c) + (b % c)) % c --- this would work for a single test value # # (a + b) % c == ((a % d) + (b % d)) % c --- if d is a multiple of c, which is why here # we use the product of all test value # total_test_value = reduce(lambda w, m: w * m.test_value, monkeys, 1) answer_2 = monkey_business( run(copy.deepcopy(monkeys), 10_000, me_worry_fn=lambda w: w % total_test_value) ) print(f"answer 2 is {answer_2}")