this post was submitted on 24 Dec 2024
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Advent Of Code
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console.log('Hello World')
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Im halfway through doing that, definitely feels wrong though. I'm curious to see if there is a good programatic way of doing it.
Dont you need a pair of broken bits? For mine, bit 6 is broken, because its just x6^y6. So I need to find where the carry bit got swapped to. Or are you suggesting that I swap my bit 6 operation with every other operation until it resolves?
In my input (and I suppose in everyone else's too) the swaps only occurred within the adder subcircuit for a single bit. In general, however, the way the problem is phrased, any two outputs can be swapped, which can lead to two broken bits per swap (but this just doesn't happen).
Mine definitely had outputs swapped between adders,
z06was justx06 XOR y06. The circuit was completely broken there.Every "pair" of bits has the same pattern of AND and XOR, and the previous "carry bit" is passed into the same OR / (XOR + AND) combo to produce an output bit and the next "carry bit". The "whole chain" is nearly right - otherwise your 44 bit inputs wouldn't give a 45 bit output - it's just a few are swapped over. (In my case, anyway - haven't seen any others.) All my swaps were either in the "same column" of GraphViz output, or the next column.
So, yeah. Either "random swaps" with "nearby" outputs, because it's nearly right and you don't need to check further away; or use the fact that this is the well-known pattern for adding two numbers in a CPU's ALU to generate the "correct" sequence, identify which ones are wrong, and output them in alphabetical order.. The answer you need doesn't even require you to pair them up.