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 2024

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[2024 Day 6] What is the optimal algorithm for Part 2? (self.advent_of_code)

submitted 2 weeks ago by Pyro to c/advent_of_code

14 comments fedilink hide all child comments

I know that we can brute force it by placing an obstacle at every valid position in the path, but is there a more elegant / efficient solution?

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

I am using same solution, and getting right count with test input, but the actual input gives too many.

Annoying, and really hard to debug. I made renderer to visualize, but unable to find the bug.

One misunderstanding was that I counted same walls twice, because the result should not count same added wall twice if it has same x,y.

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

Yeah something like that happend for me too, and later I counted too little because it would not recognise some possible solutions. Finally I solved it by just walking along the path and at each location put an obstacle in front of it and then check if the changed map results in a path enters longer than 10000 steps. Not pretty but at least it lead to the right result with a runtime of ~3 seconds. I would have saved a lot of time if I had tried the "brute force" way before, so I guess lesson learned.

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

You can track by just keeping list of all positions and movement direction, if two are same, it means that it is in a loop.