81 lines
2.4 KiB
Haskell
81 lines
2.4 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
|
|
module Main (main) where
|
|
|
|
import Control.Applicative.Permutations
|
|
import Control.Monad (void, when)
|
|
import Data.Char qualified as C
|
|
import Data.Either
|
|
import Data.Functor
|
|
import Data.List qualified as L
|
|
import Data.Map qualified as M
|
|
import Data.Maybe
|
|
import Data.Set qualified as S
|
|
import Data.Vector qualified as V
|
|
import Data.Void (Void)
|
|
import Text.Megaparsec
|
|
import Text.Megaparsec.Char
|
|
|
|
import Debug.Trace
|
|
|
|
exampleExpectedOutput = 64
|
|
|
|
data Tile = Cube | Empty | Round deriving (Eq, Ord)
|
|
instance Show Tile where
|
|
show Cube = "#"
|
|
show Empty = "."
|
|
show Round = "O"
|
|
type Row = [Tile]
|
|
type Input = [Row]
|
|
|
|
type Parser = Parsec Void String
|
|
|
|
parseTile :: Parser Tile
|
|
parseTile = char '#' $> Cube
|
|
<|> char '.' $> Empty
|
|
<|> char 'O' $> Round
|
|
|
|
parseRow :: Parser Row
|
|
parseRow = some parseTile <* eol
|
|
|
|
parseInput' :: Parser Input
|
|
parseInput' = some parseRow <* eof
|
|
|
|
parseInput :: String -> IO Input
|
|
parseInput filename = do
|
|
input <- readFile filename
|
|
case runParser parseInput' filename input of
|
|
Left bundle -> error $ errorBundlePretty bundle
|
|
Right input' -> return input'
|
|
|
|
compute :: Input -> Int
|
|
compute input = sum $ map (fst . L.foldr weight (0, 1)) (allPossibilities L.!! theOne)
|
|
where
|
|
transposedInput = L.transpose input
|
|
shift :: Int -> Row -> Row
|
|
shift n [] = replicate n Empty
|
|
shift n (Cube:xs) = replicate n Empty ++ Cube : shift 0 xs
|
|
shift n (Empty:xs) = shift (n+1) xs
|
|
shift n (Round:xs) = Round : shift n xs
|
|
weight :: Tile -> (Int, Int) -> (Int, Int)
|
|
weight Round (acc, i) = (acc + i, i+1)
|
|
weight _ (acc, i) = (acc, i+1)
|
|
theOne = start + (1_000_000_000 - start) `rem` (end - start)
|
|
(start, end) = cycle M.empty 0 allPossibilities
|
|
allPossibilities = iterate process transposedInput
|
|
process = step 4 (L.transpose . map (reverse . shift 0))
|
|
step :: Int -> (a -> a) -> a -> a
|
|
step 0 _ x = x
|
|
step n f x = step (n-1) f $ f x
|
|
cycle :: M.Map Input Int -> Int -> [Input] -> (Int, Int)
|
|
cycle m i (x:xs) = case M.lookup x m of
|
|
Just j -> (j, i)
|
|
Nothing -> cycle (M.insert x i m) (i+1) xs
|
|
|
|
main :: IO ()
|
|
main = do
|
|
example <- parseInput "example"
|
|
let exampleOutput = compute example
|
|
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
|
|
input <- parseInput "input"
|
|
print $ compute input
|
|
|