Day5.hs

module Javran.AdventOfCode.Y2017.Day5 (

) where

import Control.Monad.ST
import Data.Function
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import Javran.AdventOfCode.Prelude

data Day5 deriving (Generic)

simulate :: (Int -> Int -> Int) -> [Int] -> ST s Int
simulate modifier xs = do
  vec <- VU.unsafeThaw (VU.fromList xs)
  fix
    ( \loop cur cnt -> do
        offset <- VUM.unsafeRead vec cur
        let next = cur + offset
        if next < 0 || next >= VUM.length vec
          then pure (cnt + 1)
          else do
            VUM.unsafeModify vec (modifier offset) cur
            loop next (cnt + 1)
    )
    0
    0

instance Solution Day5 where
  solutionRun _ SolutionContext {getInputS, answerShow} = do
    xs <- fmap (read @Int) . lines <$> getInputS
    answerShow $ runST (simulate (const succ) xs)
    answerShow $ runST (simulate (\offset -> if offset >= 3 then pred else succ) xs)