Day 22: Monkey Market

Megathread guidelines

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FAQ

  • @LeixB
    link
    16 hours ago

    Haskell

    solution
    import Control.Arrow
    import Data.Bits
    import Data.List
    import qualified Data.Map as M
    
    parse = fmap (secretNums . read) . lines
    
    secretNums :: Int -> [Int]
    secretNums = take 2001 . iterate (step1 >>> step2 >>> step3)
     where
      step1 n = ((n `shiftL` 06) `xor` n) .&. 0xFFFFFF
      step2 n = ((n `shiftR` 05) `xor` n) .&. 0xFFFFFF
      step3 n = ((n `shiftL` 11) `xor` n) .&. 0xFFFFFF
    
    part1 = sum . fmap last
    part2 = maximum . M.elems . M.unionsWith (+) . fmap (deltas . fmap (`mod` 10))
    
    deltas l = M.fromListWith (\n p -> p) $ flip zip (drop 4 l) $ zip4 diffs (tail diffs) (drop 2 diffs) (drop 3 diffs)
     where
      diffs = zipWith (-) (tail l) l
    
    main = getContents >>= print . (part1 &&& part2) . parse