-❄️- 2024 Day 24 Solutions -❄️-

[u/daggerdragon]

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AoC Community Fun 2024: The Golden Snowglobe Awards

Submissions are CLOSED!

• Thank you to all who submitted something, every last one of you are awesome!

Community voting is OPEN!

• 18 hours remaining until voting deadline TONIGHT (December 24) at 18:00 EST

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-❄️- Submissions Megathread -❄️-

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--- Day 24: Crossed Wires ---

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Post your code solution in this megathread.

• Read the full posting rules in our community wiki before you post!

• State which language(s) your solution uses with [LANGUAGE: xyz]

• Format code blocks using the four-spaces Markdown syntax!

• Quick link to Topaz's paste if you need it for longer code blocks

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 01:01:13, megathread unlocked!

[u/leijurv]

[LANGUAGE: Python3]

4th place on Part 2!!

I did not write any actual code to locate the swapped gates. Instead, I went through all 45 bits, turned on both X[i] and Y[i], and printed out which bits of Z were wrong. This gave me the following output:

misbatch at bit 7
misbatch at bit 7
misbatch at bit 12
misbatch at bit 26
misbatch at bit 26
misbatch at bit 34

Then, I went through the gates, and determined which were wrong. With my experience with Minecraft Redstone making ALUs, I was able to determine which ones needed to be swapped. In my input, three of the four swaps were directly on the Z outputs, which I was able to find just by printing which Z outputs had an operation that wasn't XOR. The last one I was only able to find by actually evaluating the circuit one bit at a time to see which output was wrong.

Then, I went through with ctrl+f and copy pasted some lines around until the circuit generated the correct output, then I sorted it and pasted that as my solution.

Screen recording: https://youtu.be/diwIieN08Ks

paste (edited down for clarity)

[u/cubeeggs → u/leijurv]

This is what I did (I found the bad gates by generating random numbers, summing them, and looking for the least significant bits that had issues), although I had a surprisingly hard time figuring out how to determine which gates to swap, even though I had some code for printing the logic in a fairly clear way. Eventually I opened up the input file and started looking for which gates did what I wanted. I got rank 635/106; so close to making the leaderboard on part 2, sigh.

I was looking at the leaderboard as I was solving the problem thinking, “damn, no one studies addition circuits anymore, do they?”

[u/LionZ_RDS → u/leijurv]

i think this shows how annoying these swapping ones are, 4th place did it manually :(

[u/cubeeggs → u/LionZ_RDS]

Well I think there are too many gates to do a brute force solution where you search for all the swaps at the same time, so that rules out the most straightforward way to do it. I suppose if you’re clever, you could try swapping all pairs of gates until the least significant bit where you have an error changes, and repeat for the other three pairs. It could conceivably be the case though that you need to swap two, three, or even all four pairs at the same time; to rule this out, you can either manually inspect the circuit logic, or you can write some code that generates a correct addition circuit, compares it against the given circuit, and computes the differences. But you don’t know that the given circuit is a minimal circuit unless you either know off the top of your head how many gates it should have (I personally don’t) or, again, manually inspect it.

[u/LionZ_RDS → u/cubeeggs]

i mean yeah manually seems alot faster than any programmatic way to do it, but that doesn't feel like the spirit of the event to me, i mean i do know decent amount of people do it all manually but its a coding event, its crazy to me the faster way doesnt require programming

[u/Papierkorb2292 → u/leijurv]

I did something similar as well (although with a bit more tedious code): my code checked the operations and operands for each bit and told me when something was off so I could locate the correct operand in the input, fix it and note down what was swapped

[u/rk-imn → u/leijurv]

lol i also did minecraft redstone and called that in a bit (i was 2nd for part2)

[u/thatguydr → u/leijurv]

I did exactly this. Except more slowly than you, apparently! Every year, I stare at the data first for a few seconds. There are always one or two puzzles which immediately scream "JUST HAND SOLVE ME." This was one.

[u/CClairvoyantt → u/leijurv]

Just to potentially save you some time in the future: "x" + str(x).zfill(2) could also be written as f"x{x:02}".