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 type STInt s = STRef s Int
  11 type VInt s = V.MVector s Int
  12
  13 main :: IO ()
  14 main =
  15   do  let seed = [20, 0, 1, 11, 6, 3]
  16       -- print seed
  17       print $ part1 seed
  18       print $ part2 seed
  19
  20
  21 part1 seed = runGame seed 2020
  22 part2 seed = runGame seed 30000000
  23
  24 runGame :: [Int] -> Int -> Int
  25 runGame seed roundsNeeded =
  26   runST $
  27     do (round, word, history) <- seedGame seed roundsNeeded
  28        gameSteps roundsNeeded round word history
  29        readSTRef word
  30
  31 seedGame :: [Int] -> Int -> ST s (STInt s, STInt s,  VInt s)
  32 seedGame seed historySize =
  33   do round <- newSTRef $ length seed
  34      word <- newSTRef $ last seed
  35      history <- V.replicate historySize 0
  36      forM_ (zip (init seed) [1..]) $ \(t, s) -> V.write history t s
  37      return (round, word, history)
  38
  39
  40 -- gameSteps :: Int -> STRef s Int -> STRef s Int -> V.MVector s Int -> ST s ()
  41 gameSteps :: Int -> STInt s -> STInt s -> VInt s -> ST s ()
  42 gameSteps targetRound round word history =
  43   do roundVal <- readSTRef round
  44      if roundVal == targetRound
  45      then return ()
  46      else do
  47            wordVal <- readSTRef word
  48            wordH <- V.read history wordVal
  49            let word' = speakWord wordH roundVal
  50            V.write history wordVal roundVal
  51            modifySTRef round (+1)
  52            writeSTRef word word'
  53            gameSteps targetRound round word history
  54
  55
  56 speakWord :: Int -> Int -> Int
  57 speakWord 0 _ = 0
  58 speakWord prev now = now - prev
  59
  60