src/advent15/advent15.hs

   1 import Data.Word
   2 import Data.Bits
   3
   4 generatorAStart = 873
   5 generatorBStart = 583
   6
   7 main :: IO ()
   8 main = do
   9     print $ part1
  10     print $ part2
  11
  12 part1 = length $ filter (uncurry (==)) $ take 40000000 $ zip streamA streamB
  13
  14
  15 part2 = length $ filter (uncurry (==)) $ take 5000000 $ zip fsA fsB
  16     where fsA = filteredStream 3 streamA
  17           fsB = filteredStream 7 streamB
  18
  19
  20 generatorA = generator 2147483647 16807
  21 generatorB = generator 2147483647 48271
  22
  23 streamA = stream generatorA generatorAStart
  24 streamB = stream generatorB generatorBStart
  25
  26 generator :: Word64 -> Word64 -> Word64 -> Word64
  27 generator divisor factor n = n * factor `rem` divisor
  28
  29 toWord16 :: Word64 -> Word16
  30 toWord16 = fromIntegral
  31
  32 stream :: (Word64 -> Word64) -> Word64 -> [Word16]
  33 stream gen n0 = map toWord16 $ drop 1 $ iterate gen n0
  34
  35 filteredStream :: Word16 -> [Word16] -> [Word16]
  36 filteredStream f str = filter ((== 0) . ( .&. f)) str