Day 11: Plutonian Pebbles

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
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FAQ

  • @Acters
    3•6 hours ago

    Python

    Part 1: ~2 milliseconds, Part 2: ~35 milliseconds, Total Time: ~35 milliseconds
    You end up doing part 1 at the same time as part 2 but because of how Advent of Code works, you need to rerun the code after part 1 is solved. so Part 2 is technically total time.

    Fast Code 
    from time import time_ns

transform_cache = {}

def transform(current_stone):
    if current_stone == "0":
        res = ["1"]
    else:
        length = len(current_stone)
        if length % 2 == 0:
            mid = length // 2
            res = [str(int(current_stone[:mid])), str(int(current_stone[mid:]))]
        else:
            res = [str(int(current_stone) * 2024)]
    transform_cache[current_stone] = res
    return res

def main(initial_stones):
    stones_count = {}
    for stone in initial_stones:
        stones_count[stone] = stones_count.get(stone, 0) + 1
    part1 = 0
    for i in range(75):
        new_stones_count = {}
        for stone, count in stones_count.items():
            for r in (transform_cache.get(stone) if stone in transform_cache else transform(stone)):
                new_stones_count[r] = new_stones_count.get(r, 0) + count
        stones_count = new_stones_count
        if i == 24:
            part1 = sum(stones_count.values())
    return part1,sum(stones_count.values())

if __name__ == "__main__":
    with open('input', 'r') as f:
        input_data = f.read().replace('\r', '').replace('\n', '').split()
    start_time = time_ns()
    part_one, part_two = main(input_data)
    stop_time = time_ns() - start_time
    time_len = min(9, ((len(str(stop_time))-1)//3)*3)
    time_conversion = {9: 'seconds', 6: 'milliseconds', 3: 'microseconds', 0: 'nanoseconds'}
    print(f"Part 1: {part_one}\nPart 2: {part_two}\nProcessing Time: {stop_time / (10**time_len)} {time_conversion[time_len]}")
    • @[email protected]OPM
      1•49 minutes ago

      Stepping through this code is what made it click for me, thanks. I was really mentally locked in on “memoizing” of the transform function, instead of realizing that the transform function only needs to be applied once per stone value.

      Yours is still a lot faster than my rust version, so i’ll have to work out what is happening there.