advent15l.hs

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