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 2 SOLUTIONS -🦌 (programming.dev)

submitted 3 weeks ago by [email protected] to c/[email protected]

56 comments fedilink hide all child comments

Day 2: Red-Nosed Reports

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[–] [email protected] 8 points 3 weeks ago (4 children)

Haskell

This was quite fun! I got a bit distracted trying to rewrite safe in point-free style, but I think this version is the most readable. There's probably a more monadic way of writing lessOne as well, but I can't immediately see it.

safe xs = any gradual [diffs, negate <$> diffs]
  where
    diffs = zipWith (-) (drop 1 xs) xs
    gradual = all (`elem` [1 .. 3])

lessOne [] = []
lessOne (x : xs) = xs : map (x :) (lessOne xs)

main = do
  input :: [[Int]] <- map (map read . words) . lines <$> readFile "input02"
  print . length $ filter safe input
  print . length $ filter (any safe . lessOne) input

[–] [email protected] 4 points 3 weeks ago (3 children)

Love to see your haskell solutions!

I am so far very amazed with the compactness of your solutions, your lessOne is very much mind-Bending. I have never used or seen <$> before, is it a monadic $?

Also I can't seem to find your logic for this safety condition: The levels are either all increasing or all decreasing, did you figure that it wasn't necessary?

[–] [email protected] 2 points 3 weeks ago* (last edited 3 weeks ago)

<$> is just fmap as an infix operator.

>>> fmap (+1) [1,2,3]
[2,3,4]
>>> (+1) <\$> [1,2,3]
[2,3,4]

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