advent16.hs

   1 import Data.List (nub)
   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
  16 part1 :: IO ()
  17 part1 = print $ checksum $ take disk1length $ expand disk1length input
  18
  19 part2 :: IO ()
  20 part2 = print $ checksum $ take disk2length $ expand disk2length input
  21
  22
  23 expand :: Int -> String -> String
  24 expand len a
  25     | length a >= len = a
  26     | otherwise = expand len $ a ++ "0" ++ b
  27         where b = map (invert) $ reverse a
  28               invert '0' = '1'
  29               invert '1' = '0'
  30
  31 checksum :: String -> String
  32 checksum digits
  33     | odd $ length digits = digits
  34     | otherwise = checksum $ map (checksumPair) $ pairs digits
  35         where checksumPair p = if (length $ nub p) == 1 then '1' else '0'
  36
  37
  38 pairs :: [a] -> [[a]]
  39 pairs [] = []
  40 pairs xs = [p] ++ (pairs ys)
  41     where (p, ys) = splitAt 2 xs