I implemented the programs for hash1 and hash2, but I had to make a lot of changes to FiniteMap to get them to work: - I changed foldl to foldl' (as defined in Hugs). - I made foldFM strict (like foldl'). - I made the datatype FiniteMap strict (put !'s everywhere). I put the programs below, maybe there is a better way to do this. Jan -- Hash1 module Main(main) where import FiniteMap import System writeHex' :: Int -> String writeHex' 0 = "" writeHex' n = c:writeHex' y where x = n `mod` 16 y = n `div` 16 c | x <= 9 = toEnum ((fromEnum '0') + x) | otherwise = toEnum ((fromEnum 'A') + x - 10) writeHex :: Int -> String writeHex n | n > 0 = reverse (writeHex' n) | n == 0 = "0" | otherwise = '-':(reverse (writeHex' (-n))) main :: IO() main = do { [arg] <- getArgs; let n = read arg fm = listToFM [(writeHex i,i) | i <- [1..n]] c = sum [if elemFM (show i) fm then 1 else 0 | i <- reverse [1..n]] in putStrLn (show c); -- Hash2 module Main(main) where import FiniteMap import System import Maybe foldl' :: (a -> b -> a) -> a -> [b] -> a foldl' _ a [] = a foldl' f a (x:xs) = (foldl' f $! f a x) xs f :: FiniteMap Int Int -> FiniteMap Int Int -> Int -> FiniteMap Int Int f hash1 hash2 k | isJust elt2 = addToFM hash2 k (fromJust elt1 + fromJust elt2) | otherwise = addToFM hash2 k (fromJust elt1) where elt1 = lookupFM hash1 k elt2 = lookupFM hash2 k main :: IO() main = do { [arg] <- getArgs; let n = read arg hash1 = listToFM [(i,i) | i <- [1..10000]] keys = concat (take n (repeat (keysFM hash1))) hash2 = foldl' (f hash1) emptyFM keys; h1_1 = fromJust (lookupFM hash1 1) h1_9999 = fromJust (lookupFM hash1 9999) h2_1 = fromJust (lookupFM hash2 1) h2_9999 = fromJust (lookupFM hash2 9999) in putStrLn (show h1_1 ++ " " ++ show h1_9999 ++ " " ++ show h2_1 ++ " " ++ show h2_9999); }