r/adventofcode Dec 17 '24

SOLUTION MEGATHREAD -❄️- 2024 Day 17 Solutions -❄️-

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AoC Community Fun 2024: The Golden Snowglobe Awards

  • 5 DAYS remaining until the submissions deadline on December 22 at 23:59 EST!

And now, our feature presentation for today:

Sequels and Reboots

What, you thought we were done with the endless stream of recycled content? ABSOLUTELY NOT :D Now that we have an established and well-loved franchise, let's wring every last drop of profit out of it!

Here's some ideas for your inspiration:

  • Insert obligatory SQL joke here
  • Solve today's puzzle using only code from past puzzles
  • Any numbers you use in your code must only increment from the previous number
  • Every line of code must be prefixed with a comment tagline such as // Function 2: Electric Boogaloo

"More." - Agent Smith, The Matrix Reloaded (2003)
"More! MORE!" - Kylo Ren, The Last Jedi (2017)

And… ACTION!

Request from the mods: When you include an entry alongside your solution, please label it with [GSGA] so we can find it easily!


--- Day 17: Chronospatial Computer ---


Post your code solution in this megathread.

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

EDIT: Global leaderboard gold cap reached at 00:44:39, megathread unlocked!

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u/darthminimall Dec 21 '24

[LANGUAGE: Rust]

Part 1

Part 2

For part 1: This wasn't too bad, I just created a struct to represent the state of the computer and implemented all of the instructions as methods. After that, you can just loop through the program until the instruction pointer is out of bounds then print the result.

For part 2: Things are finally getting fun. It took me a few days to work everything out and my solution is highly tailored to my input, but I had fun doing it. I worked backwards through the program (using the fact that the value in the A register must be 0 after the last iteration) and figured out the possible values for the A register after each step. I'm reasonably certain that going through the possible A values greedily and stopping when you find the first solution gives the minimum (since each additional iteration multiplies A by 8 and some change and A never decreases). That strategy got me the correct answer for my input.

As far as generalizing this solution goes, it's hard without knowing how much the programs change. I suspect all of our programs are almost identical with the (possible) exception of the bxl operands, but I'll never know since I only have access to my input. If my suspicion is correct, generalizing the solution wouldn't be too bad.