advent-of-code/2023/13/Main1.hs

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import Data.List.Split (splitOn)
import Data.List (foldl', transpose)
import qualified Data.Vector.Unboxed as VU
import Data.Vector.Unboxed (Vector)
hashChar :: Char -> Int
hashChar '#' = 1
hashChar '.' = 0
lineToInt :: String -> Int
lineToInt = foldl' (\x y -> 2 * x + hashChar y) 0
matchesAt :: Vector Int -> Int -> Bool
matchesAt v i = VU.reverse rightSide == leftSide
where
nMirrored = min i $ VU.length v - i
leftSide = VU.slice (i - nMirrored) nMirrored v
rightSide = VU.slice i nMirrored v
findMatches :: Vector Int -> [Int]
findMatches v = filter (matchesAt v) [1 .. VU.length v - 1]
solveDirection :: [String] -> Int
solveDirection = sum . findMatches . VU.fromList . map lineToInt
solve :: [String] -> Int
solve l = 100 * solveDirection l + (solveDirection . transpose) l
main :: IO ()
main = print . sum . map (solve . lines) . splitOn "\n\n"
=<< readFile "data.txt"