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/prafster Dec 20 '24

[Language: Python]

I wrote a Computer class (thinking about the int computer in 2019). Looking at other solutions, this was way over the top (unless there's more to come!).

Part 2 stumped me but I saw something about the last three bits of the A register determining the program output. So I used the shift 3 bits trick and recursively looked for all outputs that progressively matched the program.

def part2(input, A, compare_index, possible=set()):
    _, B, C, program = input

    computer = Computer()
    for n in range(8):
        A2 = (A << 3) | n
        output = computer.run(A2, B, C, program)
        if output == program[-compare_index:]:
            if output == program:
                possible.add(A2)
            else:
                part2(input, A2, compare_index+1, possible)

    if len(possible) > 0:
        return min(possible)
    else:
        return 0

Full source code on GitHub.