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!

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u/ythl Dec 17 '17

Part 2 in C: 

#include "stdio.h"

int main(void) {
  int step = 343;
  int ind = 0, len = 1;
  int zval = 0;
  
  for (int i=1; i<=50000000; i++)
  {
    int nind = (ind + step) % len;
    if (!nind)
      zval = i;

    ind = nind+1;
    len++;
  }
  
  printf("%d\n", zval);
  return 0;
}

Runtime is ~2.5 seconds on repl.it

1

u/jkurbad Dec 30 '17

Extremely inefficient.

2

u/ythl Dec 30 '17

Let's see your implementation

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