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module Main where
import Data.Foldable (toList)
import qualified Data.IntMap.Strict as IM
import Data.IntMap.Strict (IntMap)
import Data.List (foldl')
import Input
import Util
type State = IntMap Int
next :: Int -> Int -> State -> Int
next idx num mp = maybe 0 (idx -) (IM.lookup num mp)
vaneck :: [Int] -> [Int]
vaneck values = init values ++ expand (length values) (last values) (seed (init values))
where
expand idx num state =
let num' = next idx num state
in num : expand (idx + 1) num' (IM.insert num idx state)
seed = foldl' go mempty . zip [1..]
where go mp (idx, num) = IM.insert num idx mp
main :: IO ()
main = do
input <- map read . toList . splitOn (== ',') . head <$> getInput 15 :: IO [Int]
print (vaneck input !! 2019)
print (vaneck input !! 29999999)
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