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.

AoC 2024

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💂 - 2024 DAY 6 SOLUTIONS - 💂 (programming.dev)

submitted 3 weeks ago by [email protected] to c/[email protected]

41 comments fedilink hide all child comments

Day 6: Guard Gallivant

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[–] [email protected] 2 points 3 weeks ago* (last edited 3 weeks ago) (4 children)

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?

[–] [email protected] 3 points 3 weeks ago* (last edited 3 weeks ago) (1 children)

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.

[–] [email protected] 1 points 2 weeks ago (1 children)

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 :)

[–] [email protected] 1 points 2 weeks ago

It probably won’t matter a whole deal but array indexing involves no comparisons or searches. And I found it convenient too!

[–] [email protected] 2 points 3 weeks ago* (last edited 3 weeks ago) (1 children)

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.

[–] [email protected] 2 points 2 weeks ago

I’d like to see your solution in total.

I set it up a bit like a game, https://pastebin.com/FGA6E7fA

My part one hovers around 600 microseconds.

Ohhh, that says my part 1 is slow already, i was sure my approach for 2 was the problem. Good to know!

[–] [email protected] 2 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

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

[–] [email protected] 2 points 2 weeks ago

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..

[–] [email protected] 1 points 2 weeks ago

Alright, I completely forgot about --release because i normally use just to run my stuff. That brings part 2 down to around 400ms, i am okay with that for now :D