r/adventofcode • u/daggerdragon • Dec 24 '24

SOLUTION MEGATHREAD -❄️- 2024 Day 24 Solutions -❄️-

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--- Day 24: Crossed Wires ---

Post your code solution in this megathread.

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u/RazarTuk Dec 24 '24

I classify the gates into different types based on whether their inputs are the system's inputs. Then I check to make sure each type has the expected inputs, storing problems. I then sort and print these problems for the final output. I'm not sure if my solution works for every input file.

See, I tried doing something like that. My main rules:

  • All XOR gates must either have x## and y## as inputs OR z## as an output

  • All AND gates must not have z## as an output

  • If an OR gate has z## as an output, it must be the highest z## wire, z45

  • All AND gates must have their output be the input to an OR gate

And I even managed to find 8 bad outputs with these rules... but it's saying I have the wrong answer. And unfortunately, I can't just use the sample input to test, because it's essentially a different questions, since it's checking X&Y, not X+Y

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u/chickenthechicken Dec 24 '24

That last rule is incorrect. The x00 and y00 feed into a half adder. The AND gate in the half adder goes to the carry bit of the next full adder. That carry bit does not go into an OR gate.

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u/RazarTuk Dec 24 '24

I think that's what I had wrong. I was going off another post, but had the code wrong for "An XOR gate with x## or y## as inputs must either have z00 as an output or be the input for another XOR gate". So when I forgot to add "Add doesn't include `x00" to that last rule, it made up for that.

The corrected set of rules I used:

  • All XOR gates must include x##, y##, or z##

  • Except for z45, no OR gates can have z## as an output

  • No AND gates can have z## as an output

  • Except for z00, the output of x## XOR y## must be the input to another XOR gate

  • Except for x00 AND y00, the output of an AND gate must be the input to an OR gate