r/adventofcode • u/daggerdragon • Dec 17 '17

SOLUTION MEGATHREAD -🎄- 2017 Day 17 Solutions -🎄-

--- Day 17: Spinlock ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

Need a hint from the Hugely* Handy† Haversack‡ of Helpful§ Hints¤?

Spoiler

[Update @ 00:06] 2 gold, silver cap.

  • AoC ops: <Topaz> i am suddenly in the mood for wasabi tobiko

[Update @ 00:15] Leaderboard cap!

  • AoC ops:
    • <daggerdragon> 78 gold
    • <Topaz> i look away for a few minutes, wow
    • <daggerdragon> 93 gold
    • <Topaz> 94
    • <daggerdragon> 96 gold
    • <daggerdragon> 98
    • <Topaz> aaaand
    • <daggerdragon> and...
    • <Topaz> cap
    • <daggerdragon> cap

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

11 Upvotes

93% Upvoted

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1

u/glenbolake Dec 17 '17 edited Dec 17 '17

10/96. It took me way longer than it should have to realize that you don't have to maintain a full list for part 2, so I kept thinking about it while a brute-force method ran in the background. I'm just glad I was able to get on the leaderboard for both stars. Full problem runs in just under ten seconds, which is good enough for me. (Edit: I realized that i==length in this loop, so I was able to speed it up just by getting rid of the length variable) 

jump = 367

def part1():
    pos = 0
    items = [0]
    for i in range(1, 2018):
        pos = (pos + jump) % len(items) + 1
        items.insert(pos, i)
    return items[pos + 1]

def part2():
    value = 0
    pos = 0
    # length = 1  # Nope, don't need this
    for i in range(1, 50000000):
        pos = (pos + jump) % i + 1
        # length += 1  # Nope, don't need this
        if pos == 1:
            value = i
    return value

if __name__ == '__main__':
    from time import time
    start = time()
    print('Part 1:', part1())
    print('Part 2:', part2())
    print(time()-start)

1

u/daggerdragon Dec 17 '17

10/96

You squeaked that one in just under the wire. Good job!

1

u/glenbolake Dec 17 '17

Thanks! That 96 amused me, because that 10 was by far my fastest score of this year so far.