adventofcode16/app/advent16.hs

   1 module Main(main) where
   2
   3 import Data.List (nub)
   4
   5 input = "11100010111110100"
   6 disk1length = 272
   7 disk2length = 35651584
   8
   9 -- input = "10000"
  10 -- disk1length = 20
  11
  12 main :: IO ()
  13 main = do
  14     part1
  15     part2
  16
  17 part1 :: IO ()
  18 part1 = putStrLn $ checksum $ take disk1length $ expand disk1length input
  19
  20 part2 :: IO ()
  21 part2 = putStrLn $ checksum $ take disk2length $ expand disk2length input
  22
  23
  24 expand :: Int -> String -> String
  25 expand len a
  26     | length a >= len = a
  27     | otherwise = expand len $ a ++ "0" ++ b
  28         where b = map (invert) $ reverse a
  29               invert '0' = '1'
  30               invert '1' = '0'
  31
  32 checksum :: String -> String
  33 checksum digits
  34     | odd $ length digits = digits
  35     | otherwise = checksum $ map (checksumPair) $ pairs digits
  36         where checksumPair p = if (length $ nub p) == 1 then '1' else '0'
  37
  38
  39 pairs :: [a] -> [[a]]
  40 pairs [] = []
  41 pairs xs = [p] ++ (pairs ys)
  42     where (p, ys) = splitAt 2 xs