t11

average :: [Int] -> Int
average xs = sum xs `div` length xs

average' :: [Int] -> Int
average' xs = foldr (+) 0 xs `div` length xs



splaszcz :: [[a]] -> [a]
splaszcz xss = foldl (++) [] xss



multiplyLengthLambda :: [Int] -> [Int]
multiplyLengthLambda xs = map (\x -> x * length xs) xs

multiplyLengthPartial :: [Int] -> [Int]
multiplyLengthPartial xs = map (* length xs) xs

=-=-=-=

factorial :: Int -> Int
factorial n
  | n < 0 = -1
  | n == 0 = 1
  | otherwise = n * factorial (n - 1)

factorial :: Int -> Int
factorial n = case n of
  _ | n < 0 -> -1
    | n == 0 -> 1
    | otherwise -> n * factorial (n - 1)

=-=-=-=

findLastIndex :: Eq a => a -> [a] -> Int
findLastIndex target xs = findLastIndexHelper target xs (-1) 0
  where
    findLastIndexHelper _ [] lastIndex _ = lastIndex
    findLastIndexHelper target (x:xs) lastIndex currentIndex =
      if x == target
        then findLastIndexHelper target xs currentIndex (currentIndex + 1)
        else findLastIndexHelper target xs lastIndex (currentIndex + 1)


findFirstIndex :: Eq a => a -> [a] -> Int
findFirstIndex target xs = findFirstIndexHelper target xs (-1) 0
  where
    findFirstIndexHelper _ [] lastIndex _ = lastIndex
    findFirstIndexHelper target (x:xs) lastIndex currentIndex
      | x == target = findFirstIndexHelper target xs currentIndex (currentIndex + 1)
      | otherwise = findFirstIndexHelper target xs lastIndex (currentIndex + 1)