Algorithms: design and analysis I, exercise5 (week5)

exercise5.hs

{-# LANGUAGE UnicodeSyntax #-}
import Control.Applicative ((<$>))
import Data.Foldable (foldMap)
import Data.Maybe (mapMaybe)
import Data.Monoid (Any(..))
import System.Environment (getArgs)

import qualified Data.ByteString.Lazy.Char8 as BSC
import qualified Data.HashSet as HS

main = do
  h ← readHashSet . head =<< getArgs
  putStrLn $ concatMap (show . (\x → if x then 1 else 0) . getAny . canBeProduced h)
    [231552,234756,596873,648219,726312,981237,988331,1277361,1283379]

readHashSet ∷ FilePath → IO (HS.HashSet Int)
readHashSet φ = HS.fromList . map fst . mapMaybe BSC.readInt . BSC.lines <$> BSC.readFile φ

canBeProduced ∷ HS.HashSet Int → Int → Any
canBeProduced h v = foldMap (\α → Any $ HS.member (v - α) h) h

👍