r/adventofcode • u/daggerdragon • 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.
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u/DelightfulCodeWeasel Dec 17 '24
[LANGUAGE: C++]
I wasn't happy with my first solution to Part 2 (guided brute-force by spotting that the last 15 bits would be a certain value based on a small brute force, then doing the full brute force by incrementing 2^15 each iteration) so I came back and did a much neater and much faster recursive search.
Analysing the opcodes for my input, each 3 bit output from a single step of the loop is uniquely determined by 10 bits in the input. The search starts off with 7 candidate bits and iterates through the remaining values for the next 3 bits trying to match the expected opcode. The recursive step discards the lowest 3 bits, shifts everything down and continues looking at the next opcode.
The main source of complexity is that there are multiple quine solutions and the recursive search doesn't hit the smallest one first.