Day 6: Guard Gallivant
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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
How long did brute force take? Mine was 9s on an m1 with rust.
My rust code ran in 6s on my phone (Samsung A35 running under Termux). When I’m back at a computer it’d be interesting to compare times properly.
About 15-20 seconds, not too bad.
I got mine down to 3s, but it wasn’t a very smart loop detection. All I did was count steps and stop after 10000. The 9 second run was 100000 steps, which is obviously a bit excessive.
Does save iterating over the list of past visits, so probably a good shortcut.
I did a similar approach (place obstacles on guards path). Takes about
80s10-15s in 11th Gen Intel® Core™ i7-11800H. Motivated by the code above, I also restricted the search to start right before the obstacle rather than the whole path which took it down from 80s to 10-15sThat’s about how long it takes for my python solution to complete.
How did you detect loops? I just ran for 100000 steps to see if I escaped, got my time down to 3s by doing only 10000 steps.
I added each visited position/direction to a set, and when a ‘state’ is reached again you have entered a loop:
v = set() while t[g.r][g.c] != 'X': state = (g.r, g.c, g.d) if state in v: acc += 1 break v.add(state) g.move(t)
You can view my full solution here.
Not who you asked but: I save coordinates and direction into a vector each time the guard faces a #. Also every time the guard faces a #, I check if the position exists in the vector, if true, it’s an infinite loop. 78ms rust aolution.
That’s probably quite optimal, compared with checking every state in the path, or running off a fixed number of steps