src/advent14/advent14.hs

   1 import Data.List.Split (chunksOf)
   2 import Data.Char (ord)
   3 import Text.Printf (printf)
   4 import Data.Bits (xor)
   5 import qualified Data.Map.Strict as M
   6 import qualified Data.Graph as G
   7
   8 type CellMap = M.Map (Int, Int) Bool
   9
  10 puzzleKey = "xlqgujun"
  11
  12 main :: IO ()
  13 main = do
  14   print $ part1 puzzleKey
  15   print $ part2 puzzleKey
  16
  17
  18 part1 :: String -> Int
  19 part1 key = sum rowCounts
  20     where binHashes = map binHash $ rowSpecs key
  21           rowCounts = map countSetBits binHashes
  22
  23
  24 part2 :: String -> Int
  25 part2 key = length $ cellEdges cells
  26     where binHashes = map binHash $ rowSpecs key
  27           cells = presentCells binHashes
  28
  29 binHash :: String -> String
  30 binHash = binify . knotHash
  31
  32 numKey :: (Int, Int) -> Int
  33 numKey (r, c) = 128 * r + c
  34
  35
  36 presentCells :: [String] -> CellMap
  37 presentCells binHashes = M.fromList [((r, c), True) | r <- [0..127], c <- [0..127], (binHashes!!r)!!c == '1']
  38
  39 adjacentCells :: CellMap -> (Int, Int) -> [(Int, Int)]
  40 adjacentCells cells (r, c) = filter (\k -> M.member k cells) possibles
  41   where possibles = [(r, c - 1), (r, c + 1), (r - 1, c), (r + 1, c)]
  42
  43
  44 cellEdges :: CellMap -> [G.SCC (Int, Int)]
  45 cellEdges cells = G.stronglyConnComp [(k, numKey k, map numKey $ adjacentCells cells k) | k <- M.keys cells]
  46
  47 rowSpecs :: String -> [String]
  48 rowSpecs key = map (((key ++ "-") ++) . show) ([0..127] :: [Integer])
  49
  50 countSetBits :: String -> Int
  51 countSetBits = length . filter (== '1')
  52
  53
  54
  55 knotHash :: String -> [Int]
  56 knotHash input = densify tied
  57     where (tied, _, _) = foldl step ([0..255], 0, 0) hashTerms
  58           hashTerms = mkHashTerms input
  59
  60 step :: ([Int], Int, Int) -> Int -> ([Int], Int, Int)
  61 step (original, start, skip) len = (replaced, start', skip + 1)
  62     where replaced = tie original start len
  63           start' = (start + len + skip) `mod` (length original)
  64
  65 tie :: [a] -> Int -> Int -> [a]
  66 tie original start len = replace original replacement start
  67     where replacement = reverse $ extract original start len
  68
  69 extract :: [a] -> Int -> Int -> [a]
  70 extract items from len = take len $ drop from $ items ++ items
  71
  72 replace :: [a] -> [a] -> Int -> [a]
  73 replace original replacement from = take (length original) (start ++ replacement ++ remainder)
  74     where excess = drop (length original - from) replacement
  75           stub = drop (length excess) original
  76           start = take from (excess ++ stub)
  77           remainder = drop (length $ start ++ replacement) original
  78
  79
  80 mkHashTerms :: String -> [Int]
  81 mkHashTerms text = take (length chunk * 64) $ cycle chunk
  82     where chunk = map ord text ++ [17, 31, 73, 47, 23]
  83
  84 -- hexify :: [Int] -> String
  85 -- hexify = concatMap (printf "%02x")
  86
  87 binify :: [Int] -> String
  88 binify = concatMap (printf "%08b")
  89
  90 densify :: [Int] -> [Int]
  91 densify ns = codes
  92     where chunks = chunksOf 16 ns
  93           compress = foldl1 xor
  94           codes = map compress chunks