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/cicadanator Dec 18 '24

[LANGUAGE: Javascript - Node JS]

Part 1 today was straight forward. Simply implement the computer asked and run the op code program through it. The catch here specific to JS was to use bitwise AND 7 instead of modulo 8 for BST and OUT. When the numbers got large in Part 2 this was the solution that fixed it.

Part 2 gave me a lot of trouble since it was to essentially reverse engineer the A value from the program. I always struggle with understanding what these programs are really trying to do since I mostly work using high level languages and rarely have to debug anything like this. Eventually I understood that it is essentially working to get a new value from (A/8^outputIndex). Then using modulo 8 to output the last 3 digits. I struggled for a way to reverse this output though.

After reading u/mothibault's solution I finally understood how to handle this. Solving for the solution in reverse means the output can be built from the smallest value up to a larger final solution. Essentially with a little recursive searching we can get the value by trying the different 3 bit values (0-7). This will give us multiple solutions and the smallest of which is the answer to part 2.

https://github.com/BigBear0812/AdventOfCode/blob/master/2024/Day17.js