🦌 - 2024 DAY 2 SOLUTIONS -🦌
🦌 - 2024 DAY 2 SOLUTIONS -🦌
Day 2: Red-Nosed Reports
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Haskell
This was quite fun! I got a bit distracted trying to rewrite
safein point-free style, but I think this version is the most readable. There's probably a more monadic way of writinglessOneas 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) inputLove to see your haskell solutions!
I am so far very amazed with the compactness of your solutions, your
lessOneis 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?For the last point, it isn't needed since the differences between elements should be all positive or all negative for the report to be safe. This is tested with the combination of
negateandgradual.I am also enjoying these Haskell solutions. I'm still learning the language, so it's been cool to compare my solution with these and grow my understanding of Haskell.
<$>is justfmapas an infix operator.>>> fmap (+1) [1,2,3] [2,3,4] >>> (+1) <\$> [1,2,3] [2,3,4]Thanks! The other two posters already answered your questions, I think :)
Haskell makes it really easy to build complex operations out of simple functional building blocks, skipping a lot of boilerplate needed in some other languages. I find the compactness easier to read, but I realize that not everyone would agree.
BTW, I'm a relative Haskell newbie. I'm sure more experienced folks could come up with even more interesting solutions!