AoC 2021 - day 6 part 2

day6_2.py

def advance_a_day(numbers):
    counter = 0
    for i in range(len(numbers)):
        n = numbers[i] - 1
        if n == -1:
            n = 6
            counter += 1
        numbers[i] = n
    return counter

global_cache = {i:1 for i in range(9)}

def mutate(days):
    fishes = [8]
    total_fishes = 0
    for d in range(days):
        new_fishes = advance_a_day(fishes)
        if new_fishes > 0:
            total_fishes += precalculate(days-d-1) * new_fishes

    global_cache[days] = len(fishes) + total_fishes

def precalculate(days):
    if days not in global_cache:
        mutate(days)
    
    return global_cache[days]
    
def main(file_path):
    numbers = read_data(file_path)

    fishes = [int(n) for n in numbers]
    total_fishes = 0
    max_days = 256
    for d in range(max_days):
        new_fishes = advance_a_day(fishes)
        total_fishes += precalculate(max_days-d-1) * new_fishes

    print(total_fishes + len(fishes))