Day 13: Claw Contraption
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4 points
Haskell
Whee, linear algebra! Converting between numeric types is a bit annoying in Haskell, but I’m reasonably happy with this solution.
import Control.Monad
import Data.Matrix qualified as M
import Data.Maybe
import Data.Ratio
import Data.Vector qualified as V
import Text.Parsec
type C = (Int, Int)
readInput :: String -> [(C, C, C)]
readInput = either (error . show) id . parse (machine `sepBy` newline) ""
where
machine = (,,) <$> coords <*> coords <*> coords
coords =
(,)
<$> (manyTill anyChar (string ": X") >> anyChar >> num)
<*> (string ", Y" >> anyChar >> num)
<* newline
num = read <$> many1 digit
presses :: (C, C, C) -> Maybe C
presses ((ax, ay), (bx, by), (px, py)) =
do
let m = fromIntegral <$> M.fromLists [[ax, bx], [ay, by]]
m' <- either (const Nothing) Just $ M.inverse m
let [a, b] = M.toList $ m' * M.colVector (fromIntegral <$> V.fromList [px, py])
guard $ denominator a == 1
guard $ denominator b == 1
return (numerator a, numerator b)
main = do
input <- readInput <$> readFile "input13"
mapM_
(print . sum . map (\(a, b) -> 3 * a + b) . mapMaybe presses)
[ input,
map (\(a, b, (px, py)) -> (a, b, (10000000000000 + px, 10000000000000 + py))) input
]
