advent-of-code-2022/src/Day5/Part2.hs

module Day5.Part2 (
  execute9001Operation,
  day5_2
) where

import qualified Data.Sequence as S
import Data.Foldable (toList)
import Day5.Shared

execute9001Operation :: Row -> Operation -> Row
execute9001Operation row op
  = updatedRow 
  where
    originStack = row `S.index` asInt (from op)
    targetStack = row `S.index` asInt (to op)
    movedContent = take (count op) $ content originStack
    updatedOrigin = Stack (drop (count op) $ content originStack)
    updatedTarget = Stack (movedContent ++ content targetStack)
    updatedRow = S.update (asInt $ to op) updatedTarget $ S.update (asInt $ from op) updatedOrigin row

day5_2 :: String -> String
day5_2 input = toList . findTopOfStacks $ foldl execute9001Operation row operations
  where
    (row, operations) = parseInput input