import qualified Data.Map as M

amount = 18

coins = [5, 4, 2, 1]

greedy a cs = fn a cs M.empty
  where
    fn _ [] m = m
    fn x (y:ys) m = let t = x `div` y
                     in if t > 0 then fn (x-t*y) ys (M.insert y t m)
                                 else fn x ys m

main :: IO ()
main = do
    let result = greedy amount coins == M.fromList [(1,1),(2,1),(5,3)]
    putStrLn ("greedy amount coins == M.fromList [(1,1),(2,1),(5,3)] is " ++ show result)