FLOLAC 2024 [Problem Set](https://gist.github.com/genetsai95/8cecea25a4c4d5c7b9b9275b4ab6f203)

FLOLAC_2024.hs

module Main where
-- WIP: Haven't read ch6, ch8 in [Learn You a Haskell for Great Good].

-- 0.
penultimate xs = last (init xs)
-- 1.
antepenultimate xs = penultimate (init xs)
-- 2.
-- `shiftLeft` is a helper function for `rotateLeft`
shiftLeft [] = []
shiftLeft (x:xs) = xs ++ [x]

rotateLeft n xs
  | n == 0 = xs
  | n > 0 = rotateLeft (n-1) (shiftLeft xs)
  -- TODO: check if value `n` is negative or not
-- 3.
insertElem x k xs
  | k < 0 = error "Neg K"
  | k >= 0 = (take k xs) ++ [x] ++ (drop k xs)
  -- No need to check if index K is larger than length of list xs
-- 4.
-- palindrome :: Eq a => [a] -> Bool
palindrome xs = xs == reverse xs
-- 5.
power x y 
  | y == 0 = 1
  | y == 1 = x
  | y > 1 = x * power x (y-1)
-- 6. 
-- `convertBits` is a helper function for `convertBinaryDigit`
convertBits [] _ = 0
convertBits (b:bs) n =
    (if b then 2^n else 0) + convertBits bs (n - 1)
convertBinaryDigit bits = convertBits bits (length bits - 1)
-- 7.
fib n = reverse (map fibN [0..n-1])
  where
    fibN 0 = 0
    fibN 1 = 1
    fibN k = fibN (k - 1) + fibN (k - 2)
-- 8.
-- mapFirst :: (a -> b) -> (a, c) -> (b, c)
mapFirst f (x,y) = (f x, y)
-- 9.
-- 10.
-- 11.
-- 12.
-- 13.
-- 14.
-- 15.

-- the main function
main :: IO ()
main = do
    print (penultimate [1,2,3,4,5]) -- 4
    print (antepenultimate [1,2,3,4,5]) -- 3
    print (shiftLeft [1,2,3,4,5]) -- [2,3,4,5,1]
    print (rotateLeft 3 [1,2,3,4,5]) -- [4,5,1,2,3]
    print (rotateLeft 5 [1,2,3,4,5]) -- [1,2,3,4,5]
    print (insertElem 3 3 [1,2,3,4,5]) -- [1,2,3,3,4,5]
    print (insertElem 3 30 [1,2,3,4,5]) -- [1,2,3,4,5,3]
    print(palindrome [1,2,3,4,5,4,3,2,1]) -- True
    print(palindrome [1,2,3,4,5,4,3,2,2]) -- False
    print(power 3 4) -- 81
    print(power 4 3) -- 64
    print(convertBinaryDigit [True, False, False]) -- 4
    print(fib 5) -- [3,2,1,1,0]
    print(mapFirst (+7) (4, True)) -- (11, True)