Day 22: Monkey Market
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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
