2023-02 in haskell

2023/02-Cube_Conundrum/second.hs

@@ -0,0 +1,66 @@
+-- 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.List qualified as L
+import Data.Map qualified as M
+import Data.Maybe
+import Data.Set qualified as S
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+exampleExpectedOutput = 2286
+
+data Draw = Draw Int Int Int deriving (Eq, Show)
+data Game = Game Int [Draw] deriving Show
+type Input = [Game]
+
+type Parser = Parsec Void String
+
+parseColor :: String -> Parser Int
+parseColor color = read <$> try (some digitChar <* char ' ' <* string color <* optional (string ", "))
+
+parseDraw :: Parser Draw
+parseDraw = do
+  (blue, green, red) <- runPermutation $
+    (,,) <$> toPermutationWithDefault 0 (parseColor "blue")
+         <*> toPermutationWithDefault 0 (parseColor "green")
+         <*> toPermutationWithDefault 0 (parseColor "red")
+  void . optional $ string "; "
+  return $ Draw blue green red
+
+parseGame :: Parser Game
+parseGame = do
+  id <- read <$> (string "Game " *> some digitChar <* optional (string ": "))
+  Game id <$> someTill parseDraw eol
+
+parseInput' :: Parser Input
+parseInput' = some parseGame <* 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'
+
+power :: [Int] -> Draw -> [Int]
+power [b, g, r] (Draw b' g' r') = [max b b', max g g', max r r']
+
+process :: Int -> Game -> Int
+process acc (Game id draws) = acc + product (L.foldl' power [0, 0, 0] draws)
+
+compute :: Input -> Int
+compute = L.foldl' process 0
+
+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
+