Advent Of Code

920 readers

27 users here now

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

Solution Threads

M	T	W	T	F	S	S
						1
2	3	4	5	6	7	8
9	10	11	12	13	14	15
16	17	18	19	20	21	22
23	24	25

Rules/Guidelines

Follow the programming.dev instance rules
Keep all content related to advent of code in some way
If what youre posting relates to a day, put in brackets the year and then day number in front of the post title (e.g. [2024 Day 10])
When an event is running, keep solutions in the solution megathread to avoid the community getting spammed with posts

Relevant Communities

Relevant Links

Advent of Code Homepage

Credits

Icon base by Lorc under CC BY 3.0 with modifications to add a gradient

console.log('Hello World')

founded 1 year ago

MODERATORS

[email protected]

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

submitted 2 weeks ago by [email protected] to c/[email protected]

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?

you are viewing a single comment's thread
view the rest of the comments

[–] [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.