src/advent09/advent09.hs

   1 data ParseState = ParseState
   2                     { total :: Int
   3                     , depth :: Int
   4                     , garbageCount :: Int
   5                     , readingGarbage :: Bool
   6                     , ignoreCharacter :: Bool
   7                     } deriving (Show, Eq)
   8
   9 main :: IO ()
  10 main = do
  11         text <- readFile "data/advent09.txt"
  12         print $ part1 text
  13         print $ part2 text
  14
  15
  16 part1 :: String -> Int
  17 part1 = total . process
  18
  19 part2 :: String -> Int
  20 part2 = garbageCount . process
  21
  22
  23 process :: String -> ParseState
  24 process = foldl parse ps0
  25     where ps0 = ParseState {total = 0, depth = 0, garbageCount = 0,
  26                     readingGarbage = False, ignoreCharacter = False}
  27
  28 parse :: ParseState -> Char -> ParseState
  29 parse ps c
  30     | ignoreCharacter ps = ps {ignoreCharacter = False}
  31     | c == '!' = ps {ignoreCharacter = True}
  32     | readingGarbage ps = if c == '>'
  33                           then ps {readingGarbage = False}
  34                           else ps {garbageCount = garbageCount ps + 1}
  35     | otherwise =
  36         case c of
  37             '<' -> ps {readingGarbage = True}
  38             '{' -> openGroup ps
  39             '}' -> closeGroup ps
  40             _   -> ps
  41
  42 openGroup :: ParseState -> ParseState
  43 openGroup ps = ps {depth = depth ps + 1}
  44
  45 closeGroup :: ParseState -> ParseState
  46 closeGroup ps = ps {total = total ps + depth ps, depth = depth ps - 1}