Ninety-Nine Haskell Problems, #1

-- Find the last element of a list.

one = last

two xs = xs !! (length xs - 1)

three = head . reverse

four [x] = x
four (x:xs) = four xs

five xs
  | length xs == 1 = xs !! 0
  | otherwise = five (tail xs)

six [x] = x
six xs = six $ tail xs

seven = head . aux
  where
    aux [] = []
    aux (x:xs) = aux xs ++ [x]

eight = last . id

nine xs =
  snd $
  head $ filter (\(a, b) -> a == 0) $ zip [length xs - 1,length xs - 2 .. 0] xs

ten xs =
  (\[(a, b)] -> b) $ dropWhile (\(a, b) -> a < length xs - 1) $ zip [0 ..] xs

eleven :: [a] -> a
eleven = foldl1 (\x y -> y)

twelve = head . scanr1 (\x y -> y)

thirteen xs = (snd . maximum . zip [0 ..]) xs

fourteen (x:xs) = aux x xs
  where
    aux y l@(z:zs) | null l = y
                   | null zs = z
                   | otherwise = aux z zs