adventofcode1616/app/advent16i.hs

   1 module Main(main) where
   2
   3 input = "11100010111110100"
   4 disk1length = 272
   5 disk2length = 35651584
   6
   7 -- input = "10000"
   8 -- disk1length = 20
   9
  10 main :: IO ()
  11 main = do
  12     part1
  13     part2
  14
  15 part1 :: IO ()
  16 part1 = print $ fill disk1length input
  17
  18 part2 :: IO ()
  19 part2 = print $ fill disk2length input
  20
  21 fill :: Int -> String -> String
  22 fill len filler = deBool $ checksum $ take len $ expand len $ enBool filler
  23
  24 enBool :: String -> [Bool]
  25 enBool = map (== '1')
  26
  27 deBool :: [Bool] -> String
  28 deBool = map (\b -> if b then '1' else '0')
  29
  30
  31 expand :: Int -> [Bool] -> [Bool]
  32 expand len = head . dropWhile ((<= len) . length) . iterate expandStep
  33
  34 expandStep :: [Bool] -> [Bool]
  35 expandStep a = a ++ [False] ++ b
  36         where b = map (not) $ reverse a
  37
  38 checksum :: [Bool] -> [Bool]
  39 checksum = head . dropWhile (even . length) . iterate checksumStep
  40
  41 checksumStep :: [Bool] -> [Bool]
  42 checksumStep [] = []
  43 checksumStep [x] = [x]
  44 checksumStep (x:y:xs) = (x==y):(checksumStep xs)
  45