lazy

1 files changed, 49 insertions, 0 deletions

diff --git a/2024/07/solve.hs b/2024/07/solve.hs
new file mode 100644
index 0000000..f05013b
--- /dev/null
+++ b/2024/07/solve.hs
@@ -0,0 +1,49 @@
+import           Data.Void
+import           Prelude                 hiding ( (||) )
+import           Text.Megaparsec
+import           Text.Megaparsec.Char
+import qualified Text.Megaparsec.Char.Lexer    as L
+
+type Parser = Parsec Void String
+
+data Equation = Equation Int [Int]
+
+equation :: Parser Equation
+equation = do
+  test <- L.decimal
+  string ": "
+  nums <- L.decimal `sepBy` char ' '
+  pure $ Equation test nums
+
+input :: Parser [Equation]
+input = equation `sepEndBy` char '\n'
+
+-- good enough
+(||) :: Int -> Int -> Int
+(||) b a = read $ show a ++ show b
+
+prune :: Int -> [Int] -> [Int]
+prune t = filter (<= t)
+
+combos :: Int -> [Int] -> [Int]
+combos t (n : ns) =
+  foldl (\s v -> prune t $ ((v +) <$> s) ++ ((v *) <$> s)) [n] ns
+
+combos2 :: Int -> [Int] -> [Int]
+combos2 t (n : ns) = foldl
+  (\s v -> prune t $ ((v +) <$> s) ++ ((v *) <$> s) ++ ((v ||) <$> s))
+  [n]
+  ns
+
+solve :: (Int -> [Int] -> [Int]) -> [Equation] -> Int
+solve f es = sum [ test | (Equation test _, m) <- zip es matches, m ]
+  where matches = (\(Equation test nums) -> test `elem` f test nums) <$> es
+
+main :: IO ()
+main = do
+  f <- readFile "input"
+  case runParser (input <* eof) "" f of
+    Right p -> do
+      print $ solve combos p
+      print $ solve combos2 p
+    Left err -> print $ errorBundlePretty err