Day 6: Guard Gallivant
Megathread guidelines
- Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
- You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://topaz.github.io/paste/ if you prefer sending it through a URL
FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
Rust
This one was the first real think for this year, but I ended up brute forcing it, placing a ‘#’ in every position and checking. part 2 runs in about
380ms78ms (after reducing the amount ‘#’-placements to only where the guard walks) on my 2011 core i-7, so I’m happy, even though it feels like I could have been smarter.Part 1 Part 2
I am doing the same principle brute force but it takes ~7 seconds oO
Is using a
HashSet<(Pos, Dir)>for the loop detection so expensive? My CPU shouldn’t be THAT bad…Part one around 7ms.
Also curious that i have not seen someone mention a more efficient approach, there gotta be one?
I created rows and cols vecs that keep places of blocks. When moving, I binary search the row or col, find the block that stops me. So moving whole sections at once. Otherwise used HashSet of pos and dir like you. Also in part 2, place the new block only on the path I take in part1. Part 2 is 26ms.
code
The binary search sounds smart, would reduce the pathing quite a bit i guess :)
Part 2 i approached quite the same i think, was only a couple lines of code additionally. But running 5ms 5000 times is also gonna take a while…
I draw
^>v<characters on the grid while walking, so then it’s a direct array lookup (instead of a hashtable). The representation could be better though, some kind of bitmask would beat checking against a bunch of characters.I dont change the map, i just record the steps in the hashtable. But maybe drawing on the map is indeed shaving some time off, thanks for the input :)
It probably won’t matter a whole deal but array indexing involves no comparisons or searches. And I found it convenient too!
I’d like to see your solution in total. I’m not too familiar with the nuts and bolts, but hash set is quite a bit more expensive than a simple vector, there’s a bunch of overhead incurred when executing the hashing and placing of the data, and when repeating a few thousand times it sure adds up. My part one hovers around 600 microseconds.
I set it up a bit like a game, https://pastebin.com/FGA6E7fA
Ohhh, that says my part 1 is slow already, i was sure my approach for 2 was the problem. Good to know!
Alright, I completely forgot about
--releasebecause i normally use just to run my stuff. That brings part 2 down to around 400ms, i am okay with that for now :D