advent15.hs

   1 import Text.Parsec
   2 import Text.ParserCombinators.Parsec.Number
   3
   4 type Disk = (Int -> Bool)
   5
   6 main :: IO ()
   7 main = do
   8     text <- readFile "advent15.txt"
   9     let disks = successfulParse $ parseIfile text
  10     part1 disks
  11     part2 disks
  12
  13 part1 :: [Disk] -> IO ()
  14 part1 disks = print $ head $ filter (canFall disks) [0..]
  15
  16 part2 :: [Disk] -> IO ()
  17 part2 disks = print $ head $ filter (canFall disks2) [0..]
  18     where disks2 = disks ++ [diskify 7 11 0]
  19
  20 canFall :: [Disk] -> Int -> Bool
  21 canFall ds i = all (\d -> (d i)) ds
  22
  23
  24 instructionFile = instructionLine `endBy` newline
  25 instructionLine = diskify <$> (string "Disc #" *> int)
  26                           <*> (string " has " *> int)
  27                           <*> (string " positions; at time=0, it is at position " *> int)
  28                           <*  (string ".")
  29
  30 diskify :: Int -> Int -> Int -> (Int -> Bool)
  31 diskify n size pos0 = (\i -> (size + n + pos0 + i) `mod` size == 0)
  32
  33 parseIfile :: String -> Either ParseError [Disk]
  34 parseIfile input = parse instructionFile "(unknown)" input
  35
  36 parseIline :: String -> Either ParseError Disk
  37 parseIline input = parse instructionLine "(unknown)" input
  38
  39 successfulParse :: Either ParseError [a] -> [a]
  40 successfulParse (Left _) = []
  41 successfulParse (Right a) = a