Advent-of-Code/2021/6/main2.py

# "constants":
total_fish = 0

# intialize shared data:
fish_reproducing_on_day = []

# functions:
def SimulateFishByDay(current_day):
    fish_reproducing_on_day[current_day + 7] += fish_reproducing_on_day[current_day]
    fish_reproducing_on_day[current_day + 9] += fish_reproducing_on_day[current_day]
    return fish_reproducing_on_day[current_day]

def Simulate(days):
    # reset data in case of multiple simulations:
    fish_reproducing_on_day.clear()
    for i in range(0, days + 9):
        fish_reproducing_on_day.append(0)

    for i in range(0, len(fish)):
        fish_reproducing_on_day[int(fish[i])] += 1

    grand_total = total_fish # starting fish count
    for i in range(0, days):
        grand_total += SimulateFishByDay(i)
    return grand_total

#### MAIN EXECUTION ####
fish = []
with open('data', 'r') as fp:
    fish = fp.readline().strip().split(',')

total_fish = len(fish)

print(Simulate(80))
print(Simulate(256))