Ninety-Nine Haskell Problems: #3

-- Find the K'th element of a list. The first element in the list is
-- number 1.

main :: IO ()
main = mapM_ (putStr . (\x -> if x == "eggs" then x ++ ";\n" else x ++ ", ")) $
    [ one
    , two
    , three
    , four
    , five
    , six
    , seven
    , eight
    , nine
    , ten
    , eleven
    , twelve
    , thirteen
    , fourteen
    , fifteen
    , sixteen
    , seventeen] <*> [1 .. 6] <*> [lst]

lst :: [String]
lst = ["foo", "bar", "baz", "ham", "spam", "eggs"]

one :: Int -> [a] -> a
one n xs = xs !! (n - 1)

two :: Int -> [a] -> a
two n xs = head $ drop (n - 1) xs

three :: Int -> [a] -> a
three n xs = last $ take n xs

four :: Int -> [a] -> a
four n xs = reverse xs !! (length xs - n)

five :: Int -> [a] -> a
five n xs = head $ drop (length xs - n) (reverse xs)

six :: Int -> [a] -> a
six n xs = last $ take (length xs + 1 - n) (reverse xs)

seven :: Int -> [a] -> a
seven n xs = last $ fst $ splitAt n xs

eight :: Int -> [a] -> a
eight n xs = head $ snd $ splitAt (n - 1) xs

nine :: Int -> [a] -> a
nine = aux 0
  where
    aux l n (y:ys)
      | l == (n - 1) = y
      | otherwise = aux (l + 1) n ys

ten :: Int -> [a] -> a
ten n xs = snd $
           head $
           filter (\t -> n == fst t) $ zip [1..] xs

eleven :: Int -> [a] -> a
eleven n xs = snd $
  foldl1 (\(f, s) (f1, s1) -> if f == n then (f, s) else (f1, s1)) $
  zip [1..] xs

twelve :: Int -> [a] -> a
twelve n xs = snd $
  head $
  zip [1..] xs >>= (\(f, s) -> [(f, s) | f == n])

thirteen :: Int -> [a] -> a
thirteen n xs = snd $ last $ zip [1 .. n] xs

fourteen :: Int -> [a] -> a
fourteen n xs = head [snd x | x <- zip [1..] xs, fst x == n]

fifteen :: Int -> [a] -> a
fifteen n (x:xs) = if n == 1 then x else fifteen (n - 1) xs

sixteen :: Int -> [a] -> a
sixteen n xs = snd $
  head $
  scanr1 (\(f, s) (f1, s1) -> if f == n then (f, s) else (f1, s1)) $
  zip [1..] xs

seventeen :: Int -> [a] -> a
seventeen n xs = aux (length xs) n xs
  where
    aux ll n (y:ys) = if ll - length ys == n then y else aux ll n ys

-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;
-- foo, bar, baz, ham, spam, eggs;