Advent of code - Day 6


On day 6 we need to count the total number of fish after n days given that each fish can spawn another fish every 6 days.

The main challenge was handling exponential growth. So instead of tracking the fish, we need to track the counts of fish for each day.

  1. How many fish are there after 80 days of exponential growth
  2. How many fish are there after 256 days of exponential growth

The counts are tracked in a pair of dicts.

  • One dict for the current day
  • A second dict for the next day count
def simulate(timers, days=80):
    day_counts = dict(Counter(timers))

    day = 0
    while day < days:
        next_day_counts: Dict[int, int] = defaultdict(int)
        for f in range(1, 9):
            next_day_counts[f - 1] += day_counts.get(f, 0)
        next_day_counts[6] += day_counts.get(0, 0)
        next_day_counts[8] += day_counts.get(0, 0)

        day_counts = copy(next_day_counts)
        day += 1
    return sum(list(day_counts.values()))

Part 1

For part 1 we simulate for 80 days

def day6_1(timers):
    return simulate(timers, 80)

Part 2

For part 2 we simulate over 256 days

def day6_2(timers):
    return simulate(timers, 256)
Dwight Gunning

Dwight Gunning