Advent Of Code

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An unofficial home for the advent of code community on programming.dev! Other challenges are also welcome!

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.

Everybody Codes is another collection of programming puzzles with seasonal events.

AoC 2025

Solution Threads

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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

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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 2 years ago

MODERATORS

Ategon@programming.dev

Sigmatics@lemmy.ca

CameronDev@programming.dev

hades@programming.dev

🎁 - 2025 DAY 9 SOLUTIONS - 🎁 (programming.dev)

submitted 2 weeks ago by CameronDev@programming.dev to c/advent_of_code@programming.dev

25 comments fedilink hide all child comments

Day 9: Movie Theater

Megathread guidelines

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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

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[–] addie@feddit.uk 2 points 1 week ago (1 children)

On the line -> inside. The calculation I've done is a bit tricksy - vertical lines include the endpoints but horizontal lines exclude them, so that the even-odd rule is followed properly if you're on the same row as corners. No lines overlap.

I'd considered using the dot product to work out whether the line turned left or right, but there's a lot of cases to consider and get right. Fair play on computing the normals.

[–] sjmulder@lemmy.sdf.org 1 points 1 week ago

How would you then distinguish between the situations in these two examples?

   ...#x
-> .###x
   .#xxx

   .....
-> .###.
   .#x#.