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๐ - 2025 DAY 9 SOLUTIONS - ๐
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this post was submitted on 09 Dec 2025
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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.
EC 2025
AoC 2025
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| 8 | 9 | 10 | 11 | 12 |
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My initial attempt on even-odd got me in trouble with the outline, as given, being 1 unit wide, not zero-width. I had to compute normals to find out outline around the tiles. You write "on the line -> outside" but don't many legal rectangle candidates sit on the edge?
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.
How would you then distinguish between the situations in these two examples?