overslept

1 files changed, 53 insertions, 0 deletions

diff --git a/2024/03/solve.hs b/2024/03/solve.hs
new file mode 100644
index 0000000..38e143e
--- /dev/null
+++ b/2024/03/solve.hs
@@ -0,0 +1,53 @@
+-- I had expected a more complex syntax in p2 :)
+
+import           Data.Functor
+import           Data.Void
+import           Text.Megaparsec
+import           Text.Megaparsec.Char
+import qualified Text.Megaparsec.Char.Lexer    as L
+
+type Parser = Parsec Void String
+type Enabled = Bool
+
+data Instr = Mul Int Int | Do | Dont | Garbage
+  deriving Show
+
+multiplication :: Parser Instr
+multiplication = do
+  string "mul("
+  a <- L.decimal
+  string ","
+  b <- L.decimal
+  string ")"
+  pure $ Mul a b
+
+program :: Parser [Instr]
+program =
+  many
+    $   try multiplication
+    <|> (string "don't()" $> Dont)
+    <|> (string "do()" $> Do)
+    <|> (satisfy (const True) $> Garbage)
+
+
+part1 :: [Instr] -> Int
+part1 = sum . map eval
+ where
+  eval (Mul a b) = a * b
+  eval _         = 0
+
+part2 :: Enabled -> [Instr] -> Int
+part2 True  (Mul a b : is) = a * b + part2 True is
+part2 True  (Dont    : is) = part2 False is
+part2 False (Do      : is) = part2 True is
+part2 e     (_       : is) = part2 e is
+part2 _     []             = 0
+
+main :: IO ()
+main = do
+  f <- readFile "input"
+  case runParser (program <* eof) "" f of
+    Right p -> do
+      print $ part1 p
+      print $ part2 True p
+    Left err -> print $ errorBundlePretty err