advent15/src/advent15.hs

   1 -- import Debug.Trace
   2
   3 import Prelude hiding (round)
   4 import Control.Monad
   5 import Control.Monad.ST
   6 import Data.STRef
   7 import qualified Data.Vector.Unboxed.Mutable as V
   8
   9
  10 main :: IO ()
  11 main =
  12   do  let seed = [20, 0, 1, 11, 6, 3]
  13       -- print seed
  14       print $ part1 seed
  15       print $ part2 seed
  16
  17
  18 part1 seed = runGame seed 2020
  19 part2 seed = runGame seed 30000000
  20
  21 zeroInt :: Int
  22 zeroInt = 0
  23
  24 seedGame seed historySize =
  25   do round <- newSTRef $ length seed
  26      word <- newSTRef $ last seed
  27      history <- V.replicate historySize zeroInt
  28      forM_ (zip (init seed) [1..]) $ \(t, s) -> V.write history t s
  29      return (round, word, history)
  30
  31 runGame seed roundsNeeded =
  32   runST $
  33     do (round, word, history) <- seedGame seed roundsNeeded
  34        gameStep roundsNeeded round word history
  35        readSTRef word
  36
  37 gameStep :: Int -> STRef s Int -> STRef s Int -> V.MVector s Int -> ST s ()
  38 gameStep targetRound round word history =
  39   do roundVal <- readSTRef round
  40      if roundVal == targetRound
  41      then return ()
  42      else do
  43            wordVal <- readSTRef word
  44            wordH <- V.read history wordVal
  45            let word' = speakWord wordH roundVal
  46            V.write history wordVal roundVal
  47            modifySTRef round (+1)
  48            writeSTRef word word'
  49            gameStep targetRound round word history
  50
  51
  52 speakWord :: Int -> Int -> Int
  53 speakWord 0 _ = 0
  54 speakWord prev now = now - prev
  55
  56