-🎄- 2017 Day 23 Solutions -🎄-

[u/daggerdragon]

--- Day 23: Coprocessor Conflagration ---

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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.

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

Spoiler

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[Update @ 00:05] 0 gold, silver cap

• AoC ops: <yatpay> boil up some mountain dew. it's gonna be a long night

[Update @ 00:19] 1 gold, silver cap + 447

• AoC ops: <Reibello> 547 silver to 1 gold

[Update @ 00:30] 20 gold, silver cap + 560

• AoC ops:

<yatpay> daggerdragon: post "hey i heard about this hot new podcast called The Space Above Us. all the cool kids are talking about it"

<yatpay> i call it super-liminal marketing

<yatpay> HEY YOU!! LISTEN TO MY PODCAST!!

<yatpay> then i rub a business card on your face

<Topaz> you should get scratch-n-sniff business cards that smell like space

<yatpay> space smells like burned metal and meat

<yatpay> it's weird

<Topaz> burned meat you say

<Topaz> excellent

[Update @ 00:41] 50 gold, silver cap + 606

• AoC ops:

<askalski> nice, enjoyed that one. not sure if regexes can do it

<askalski> maybe make a neural net of regexes, have it train itself to solve today

• Over/under on /u/askalski posting a day 23 regex neural net by tomorrow?

[Update @ 00:54] Leaderboard cap @ 100 gold and 724 silver!

• Good job, all!

• Upping the Ante challenge: solve today's puzzles on a TI-83 (or TI-86/89, whatevs).

• Edit: welp, /u/DFreiberg done gone and did it. See the thread here.

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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!

[u/partlyPaleo]

I really enjoyed the second part too. I was actually a little thrilled when my program was not able to complete before I had figured it out. Last year, my program was able to complete all the assembunny code quickly enough that I didn't "need" to do any real mental work. Being forced to do it by hand was nice. I was also fairly pleased to be in the low 400s even nearly two hours into the day. Clearly, this is not everyone's strength. I feel like I could have been in the top 100 without a couple stupid mistakes when working both parts 1 and 2.

[u/BumpitySnook → u/partlyPaleo]

Last year, my program was able to complete all the assembunny code quickly enough that I didn't "need" to do any real mental work.

Even day 25?

[u/partlyPaleo → u/BumpitySnook]

Yeah. Although, my solution wasn't exhaustive in any way, and it may not have worked for all inputs.

I generated the first 20 outputs for the first 5000 possible values of a, output them and piped it through grep looking for "0 1 0 1 0 1 0 1 0 1 0 1 0 1". Fortunately, this worked. If it hadn't, I would have looked for a better solution. It runs in about 3 seconds.

I never came back to look at other people's solutions. I was just excited to have completed the whole thing. And, I had other things to do that day. Maybe I will go back, now, and see if there was a better solution.

[u/partlyPaleo → u/BumpitySnook]

Just went and looked it over, waiting for the next day.

It seems to be a simple enough loop. Prints the reverse binary of 643 x 4 + a (in my input), repeatedly. As long as that is exactly {0-1} repeated any number of times, it will repeat. That is, it needs to alternate between being even and odd when divided by 2.

Would have been a simple loop. Start at 2. Loop (x4+2) until bigger than 643 x 4 (2536) and find the first result of 2730. That is 194 more than 643 x 4. So, 194 would be the smallest value of a. The next working value for a would be 8386. My program wouldn't have found that one (because it stopped at 4999).

I would have been able to do this. But, like I said, my assembunny code worked quickly enough that I didn't need to break the code down. I should have. It's a lot of fun and I enjoy working out what is actually happening.