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Day 9 - Part 1 refactor with state

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This commit is contained in:
Jens Kadenbach
2022-12-09 17:56:20 +01:00
parent 9bd3d62eec
commit dc5a757eb6
2 changed files with 21 additions and 11 deletions
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28
src/Day9.hs
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@@ -19,7 +19,8 @@ module Day9
where
import Control.Arrow ((>>>))
import Data.List (nub)
import Control.Monad.Trans.State.Strict (State, runState, modify)
import qualified Data.Set as S
newtype Move = Move (Int, Int)
deriving (Show, Eq)
@@ -49,17 +50,26 @@ type Pos = (Int, Int)
data Grid = Grid {h :: Pos, t :: Pos} deriving (Show, Eq)
recordPositions :: [Step] -> [Pos]
recordPositions steps = nub (lastTailPos:positions)
data MovementLog = MovementLog { visited :: S.Set Pos, recordedSteps :: [Step] }
deriving (Show, Eq)
appendOne :: (Pos, Step) -> MovementLog -> MovementLog
appendOne (p, s) (MovementLog v steps) =
MovementLog (S.insert p v) (s:steps)
recordPositions :: [Step] -> ([Pos], [Step])
recordPositions steps = (allPositions, allSteps)
where
(positions, _, Grid { t = lastTailPos}) = recordPositions' [] steps startGrid
recordPositions' :: [Pos] -> [Step] -> Grid -> ([Pos], [Step], Grid)
recordPositions' pos [] grid = (pos, [], grid)
recordPositions' pos (m : ms) Grid {h = headPos, t = tailPos} =
allPositions = S.toList $ S.insert lastTailPos (visited state)
allSteps = reverse (recordedSteps state)
((_, Grid { t = lastTailPos}), state) = runState (recordPositions' steps startGrid) (MovementLog S.empty [])
recordPositions' :: [Step] -> Grid -> State MovementLog ([Step], Grid)
recordPositions' [] grid = return ([], grid)
recordPositions' (m : ms) Grid {h = headPos, t = tailPos} =
let newHead = headPos `step` m
followStep = follow newHead tailPos
newTail = tailPos `step` followStep
in recordPositions' (tailPos : pos) ms Grid {h = newHead, t = newTail}
in modify (appendOne (newTail, followStep)) >> recordPositions' ms Grid {h = newHead, t = newTail}
startGrid :: Grid
startGrid = Grid {h = p, t = p}
@@ -106,5 +116,5 @@ day9 = do
input <- readFile "ressources/day09-input"
putStrLn "Day9"
let movements = parseMovements input
let positions = concatMap normalizeMovement >>> recordPositions >>> length $ movements
let positions = concatMap normalizeMovement >>> recordPositions >>> fst >>> length $ movements
putStrLn ("Number of distinct positions " ++ show positions)