this post was submitted on 17 Dec 2024
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Advent Of Code

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Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

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Day 17: Chronospatial Computer

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[โ€“] [email protected] 3 points 1 month ago (1 children)

I'm confused reading the buildQuine() method. It reads to me that when you call it from the top level with top = true, A0 will be set to 0, and then when we get to the 0 to 8 loop, the 'A' register will be 0 * 8 + 0 for the first iteration, and then recurse with top = false, but with a0 still ending up 0, causing infinite recursion.

Am I missing something?

I got it to work with a check that avoids the recursion if the last state's A register value is the same as the new state's value.

[โ€“] [email protected] 3 points 1 month ago

Oh, good catch. That's certainly the case if an initial value of 0 correctly generates the required value of the quine. As I'd already started running some code against the live data that's what I tested against, and so it's only when I just tested it against the example data that I saw the problem.

I have changed the for-loop to read for (var a in (top ? 1 : 0).to(8)) for maximum terseness :-)

That still works for the example and my live data, and I don't think there should be a valid solution that relies on the first triplet being 0. Thanks for your reply!