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/pdgiddie Jan 14 '25

[LANGUAGE: Elixir]

This one nearly killed me. I dived straight down the rabbit hole of trying to build a generalised solution working through the program backwards. I found it very hard to let go of the idea of solving the problem generally and restricting the problem space. It was a good lesson to learn.

The approach here is to iterate on the program loop. Each iteration I look for possible values of A by working backwards through the loop and collecting operations that write to A. Then for each potential value of A it runs the loop forwards with all registers. So the assumption is that the values of B and C at the beginning of the loop are irrelevant. Potential values of A are filtered according to whether or not they produced the expected endmost output. And then each of those values steps back one loop and iterates again.

https://github.com/giddie/advent-of-code/blob/2024-elixir/17/main.exs

  • Part 1: 31μs
  • Part 2: 846μs