Now with use of monad loops

[advent-of-code-20.git] / advent15 / src / advent15loop.hs

diff --git a/advent15/src/advent15loop.hs b/advent15/src/advent15loop.hs
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+++ b/advent15/src/advent15loop.hs
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+-- import Debug.Trace
+
+import Prelude hiding (round)
+import Control.Monad
+import Control.Monad.ST
+import Control.Monad.Loops
+import Data.STRef
+import qualified Data.Vector.Unboxed.Mutable as V
+
+
+main :: IO ()
+main = 
+  do  let seed = [20, 0, 1, 11, 6, 3]
+      -- print seed
+      print $ part1 seed
+      print $ part2 seed
+
+
+part1 seed = runGame seed 2020
+part2 seed = runGame seed 30000000
+
+runGame seed roundsNeeded =
+  runST $ 
+    do (round, word, history) <- seedGame seed roundsNeeded
+       gameLoop roundsNeeded round word history
+       readSTRef word
+
+-- gameLoop targetRound round word history =
+--     do ( gameStep round word history 
+--          `untilM_` (do r <- readSTRef round
+--                        return $ r == targetRound)
+--         )
+--        return ()
+
+-- gameLoop targetRound round word history =
+--     do untilM_ (gameStep round word history ) 
+--                (do r <- readSTRef round
+--                    return $ r == targetRound )
+--        return ()
+
+-- gameLoop targetRound round word history =
+--     do whileM_ (do r <- readSTRef round
+--                    return $ r /= targetRound )
+--                (gameStep round word history ) 
+--        return ()
+
+gameLoop targetRound round word history =
+    do whileM_ (do r <- readSTRef round
+                   return $ r /= targetRound )
+               $ gameStep round word history
+       return ()
+
+seedGame seed historySize = 
+  do round <- newSTRef $ length seed
+     word <- newSTRef $ last seed
+     history <- V.replicate historySize 0
+     forM_ (zip (init seed) [1..]) $ \(t, s) -> V.write history t s
+     return (round, word, history)
+
+gameStep :: STRef s Int -> STRef s Int -> V.MVector s Int -> ST s ()
+gameStep round word history =
+  do roundVal <- readSTRef round
+     wordVal <- readSTRef word
+     wordH <- V.read history wordVal
+     let word' = speakWord wordH roundVal
+     V.write history wordVal roundVal
+     modifySTRef round (+1)
+     writeSTRef word word'
+     return ()
+
+speakWord :: Int -> Int -> Int
+speakWord 0 _ = 0
+speakWord prev now = now - prev
+
+