this post was submitted on 08 Dec 2023
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Advent Of Code
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An unofficial home for the advent of code community on programming.dev!
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.
AoC 2023
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| 1 | 2 | 3 | ||||
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| 18 | 19 | 20 | 21 | 22 | 23 | 24 |
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console.log('Hello World')
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Rust
As others have shown, part 2 can be pretty simple if you allow one assumption: The distance from a start point to the nearest end point is always the same as cycling from that nearest end point back to itself. Under that assumption you can just take the lowest common multiple of these distances. And honestly, who can claim to understand ghost navigation and what you can and can't assume? Empirical evidence suggests that this is how ghosts travel.
Personally, I'm not a fan of requiring analysis of the individualized input to reach the correct (sufficiently efficient) solution for part 2. Or maybe I'm just resentful because I feel like I've been duped after writing an generalized-to-the-puzzle-description-but-insufficiently-efficient solution. ๐
These quantum ghosts need to come back down to reality.
Perhaps there's a mathematical way to prove that this assumption will actually always happen despite the input? I wanted to test this assumption, and edited the map and randomly changes the destinations for keys ending in Z, and it looks like the matches are still at consistent intervals. Is it possible to have an input map which breaks the assumption?
I crafted a simple counter-example (single letters for brevity). The way the sequence goes totally depends on the instructions, and we don't have any guarantees on that. It could be anything. Of course, looking at the input data we could find what the instructions are, but the assumption doesn't hold in general.
Here the distance of Z cycling back into itself could be 2 or 4, depending on what the instruction string is doing.