leetcode_sum_numbers_encoded_as_linked_list_of_digits.hs

data List a = Cons a (List a) | Nil

listA = Cons 0 (Cons 2 (Cons 4 Nil))
listB = Cons 1 (Cons 0 (Cons 1 Nil))

tentothe :: Double -> Double
tentothe m = 10 ** m

reduce :: List Double -> Double -> Double
reduce (Cons n Nil) m = n * (tentothe m)
reduce (Cons n l) m   = (reduce l (m + 1)) + (n * (tentothe m))

construct :: Double -> Double -> List Double
construct n m = Cons (extract n m) (if swallowed n (m + 1) then Nil else construct n (m + 1))

extract :: Double -> Double -> Double
extract n m = dfloor (n/tentothe m) - (dfloor (n/tentothe (m+1)) * 10)

dfloor :: Double -> Double
dfloor = fromIntegral . floor

-- extract' :: Double -> Double -> Double
-- extract' n m =  dfloor (n/tentothe m) - (dfloor (n/tentothe (m+1)) * 10)

swallowed :: Double -> Double -> Bool
swallowed n m = (n / tentothe m) < 1

sumLists a b = construct ((reduce a 0) + (reduce b 0)) 0

listToArray :: List a -> [a]
listToArray (Cons e Nil) = [e]
listToArray (Cons e l) = e : (listToArray l)

main :: IO ()
-- main = print $ extract 1234 0
main = print $ listToArray $ sumLists listA listB