import Data.Char
import Data.List

-- Exercise 1

squareDigits :: Int -> Int
squareDigits n = read (concat (map (\c -> if not (c == '-') then show ((digitToInt c)^2) else c : "") (show n))) :: Int

-- Exercise 2

data Stock = Stock String Int

stocklist :: [Stock] -> [Char] -> [(Char,Int)]
stocklist [] _ = []
stocklist _ [] = []
stocklist l m = map (\cat -> (cat, foldr (\(Stock c n) acc -> if cat == head c then acc + n else acc) 0 l)) m

-- Exercise 3

matching :: String -> [(Int, Int)]
matching s = calc s 0 []
  where
    calc [] _ _ = []
    calc s i stack = case head s of
                          '['       ->                    calc (tail s) (i + 1) (i : stack)
                          ']'       -> (head stack, i) : (calc (tail s) (i + 1) (tail stack))
                          otherwise ->                    calc (tail s) (i + 1) stack

-- Exercise 4

data BTree a = Nil | Node a (BTree a) (BTree a)

nodeCount :: BTree a -> Int
nodeCount Nil = 0
nodeCount (Node _ t1 t2) = 1 + nodeCount t1 + nodeCount t2

treeHeight :: BTree a -> Int
treeHeight Nil = 0
treeHeight (Node _ t1 t2) = 1 + max (treeHeight t1) (treeHeight t2)

isPerfectlyBalanced :: BTree a -> Bool
isPerfectlyBalanced t = nodeCount t == (2^treeHeight t) - 1

main :: IO()
main = do
  print(squareDigits 9119)
  print(squareDigits (-9119))

  let stocks = [Stock "ABAR" 200, Stock "CDXE" 500, Stock "BKWR" 250, Stock "BTSQ" 890, Stock "DRTY" 600]
  print(stocklist stocks ['A','B']) -- ➝ [('A',200),('B',1140)]
  print(stocklist stocks ['C','X']) -- ➝ [('C',500),('X',0)]
  print(stocklist stocks ['Y','X']) -- ➝ [('Y',0),('X',0)]
  print(stocklist stocks ['C'])     -- ➝ [('C', 500)]

  print(matching "1234")     -- ➝ []
  print(matching ",[.[-],]") -- ➝ [(3,5),(1,7)]
  print(matching ",+[-.,+]") -- ➝ [(2,7)]
  print(matching "[][]")     -- ➝ [(0,1),(2,3)]

  let t1 = Node 'H' (Node 'a' (Node 'k' Nil Nil)
                              (Node 'e' Nil Nil))
                    (Node 's' (Node 'l' Nil Nil)
                              (Node 'I' Nil Nil))
  print(isPerfectlyBalanced t1) -- == True