extractDigits :: Int -> [Int]
extractDigits num 
  | num == 0  = []
  | otherwise = extractDigits (num `div` 10) ++ [num `mod` 10]

noRepeatingDigits :: Int -> Bool
--noRepeatingDigits num = 
--  -- head d /= d!!1 && head d /= d!!2 && head d /= d!!3 && 
--  d!!0 /= d!!1 && d!!0 /= d!!2 && d!!0 /= d!!3 && 
--  d!!1 /= d!!2 && d!!1 /= d!!3 && 
--  d!!2 /= d!!3
--    where d = extractDigits num
noRepeatingDigits num = noRepeats (extractDigits num)

noRepeats :: [Int] -> Bool
noRepeats []     = True
noRepeats (x:xs) = not (x `elem` xs) && (noRepeats xs)

-- noRepeatingDigits 1234
-- noRepeatingDigits 1231

numBulls :: Int -> Int -> Int
numBulls num1 num2 = if length d1 == length d2 && noRepeatingDigits num1 && noRepeatingDigits num2 then 
                        numBullsHelper d1 d2 
                     else 
                        -1
                     where d1 = extractDigits num1
                           d2 = extractDigits num2

numBullsHelper :: [Int] -> [Int] -> Int
numBullsHelper [] [] = 0
numBullsHelper (x:xs) (y:ys) = if x == y then 1 + numBullsHelper xs ys else numBullsHelper xs ys

-- numBulls 1234 1235

numCows :: Int -> Int -> Int
numCows num1 num2 = if length d1 == length d2 && noRepeatingDigits num1 && noRepeatingDigits num2 then
                      numCowsHelper d1 d2 - numBullsHelper d1 d2
                    else
                      -1
                    where d1 = extractDigits num1
                          d2 = extractDigits num2
        
numCowsHelper :: [Int] -> [Int] -> Int
numCowsHelper [] _     = 0
numCowsHelper (x:xs) y = if x `elem` y then 1 + numCowsHelper xs y else numCowsHelper xs y

-- numCows 1234 4326