ACM国際大学対抗プログラミングコンテスト(A)

via http://d.hatena.ne.jp/zyxwv/20070606
入出力はサボった。

• http://www.acm-japan.org/past-icpc/domestic2006/contest/all_ja.html#section_A

{-
  http://www.acm-japan.org/past-icpc/domestic2006/contest/all_ja.html#section_A    
  2007.06.06
  nisikawa
-}
import Control.Arrow

progress :: Int -> Int -> [Int]
progress x y = iterate (+ y) x

primes :: [Int] -> [Int]
primes = filter prime . filter odd 
  where prime x = and $ map ((/= 0) . mod x) [2..x -1] 

newtype Dirichlet a b = Dirichlet {run :: a -> b}

instance Arrow Dirichlet where
    arr f = Dirichlet f
    (Dirichlet f) >>> (Dirichlet g) = Dirichlet $ g . f 
    first (Dirichlet f) = Dirichlet (first f)

exec :: Int -> Int -> Int -> Int 
exec x y z 
    | even x && even y = 0 
    | otherwise = run f y 
  where f :: Dirichlet Int Int 
        f = arr (progress x) >>> arr primes >>> arr (flip (!!) (z - 1))