advent04.hs

   1 import Data.List (last, intersperse, sortBy, intercalate, isInfixOf)
   2 import Data.List.Split (splitOn)
   3 import Data.Char (isLetter, ord, chr)
   4 import qualified Data.Map.Lazy as Map
   5 import Data.Tuple (swap)
   6
   7 data Room = Room { name :: String
   8                  , sector :: Int
   9                  , checksum :: String
  10                  } deriving (Show)
  11
  12 main :: IO ()
  13 main = do
  14         instrText <- readFile "advent04.txt"
  15         let rooms = map (parseLine) $ lines instrText
  16         part1 rooms
  17         part2 rooms
  18
  19
  20 part1 :: [Room] -> IO ()
  21 part1 rooms = do
  22     print $ sum $ map (sector) validRooms
  23     where
  24         validChecksum room = (checksum room) == makeChecksum (name room)
  25         validRooms = filter (validChecksum) rooms
  26
  27 part2 :: [Room] -> IO ()
  28 part2 rooms = do
  29     print $ filter (\sn -> isInfixOf "north" (snd sn)) sectorNames
  30     where
  31         validChecksum room = (checksum room) == makeChecksum (name room)
  32         validRooms = filter (validChecksum) rooms
  33         sectorNames = [((sector r),
  34             shiftWord (sector r) (name r)) | r <- validRooms]
  35
  36
  37 parseLine :: String -> Room
  38 parseLine line = Room {name=name, sector=sector, checksum=checksum}
  39     where components = splitOn "-" line
  40           -- name = concat $ intersperse "-" $ reverse $ tail $ reverse components
  41           name = intercalate "-" $ reverse $ tail $ reverse components
  42           sector = read $ head $ splitOn "[" $ last components
  43           checksum = filter (isLetter) $ last components
  44
  45 countedLetters :: String -> [(Char, Int)]
  46 countedLetters name = sortBy sortCLetter $ unsortedCountedLetters name
  47     where unsortedCountedLetters name = Map.toList $ Map.fromListWith (+) [(c, 1) | c <- filter (isLetter) name]
  48
  49 sortCLetter :: (Char, Int) -> (Char, Int) -> Ordering
  50 sortCLetter (l1, n1) (l2, n2)
  51     | n1 < n2 = GT
  52     | n1 > n2 = LT
  53     | n1 == n2 = compare l1 l2
  54
  55 makeChecksum :: String -> String
  56 makeChecksum name = [l | (l, _) <- take 5 $ countedLetters name]
  57
  58
  59 shiftWord :: Int -> String -> String
  60 shiftWord shift letters = map (shiftLetter shift) letters
  61
  62 shiftLetter :: Int -> Char -> Char
  63 shiftLetter shift letter
  64     | isLetter letter = chr $ (ord letter - ord 'a' + shift) `mod` 26 + ord 'a'
  65     | otherwise = ' '