1 files changed, 43 insertions, 0 deletions
diff --git a/2021/10.hs b/2021/10.hs
new file mode 100644
index 0000000..ab90d88
--- /dev/null
+++ b/2021/10.hs
@@ -0,0 +1,43 @@
+{-# OPTIONS -Wno-type-defaults #-}
+module Main where
+
+import Data.List
+import Data.Maybe
+
+import Input
+
+
+closing :: Char -> Maybe Char
+closing '(' = Just ')'
+closing '[' = Just ']'
+closing '{' = Just '}'
+closing '<' = Just '>'
+closing _ = Nothing
+
+score1 :: Char -> Int
+score1 ')' = 3
+score1 ']' = 3 * 19
+score1 '}' = 3^2 * 7 * 19
+score1 '>' = 3^3 * 7^2 * 19
+score1 _ = 0
+
+score2 :: Char -> Int
+score2 = fromMaybe 0 . fmap succ . flip elemIndex ")]}>"
+
+data Result = SErr Char | Incomplete String | Ok
+  deriving (Show)
+
+parse :: String -> Result
+parse = go []
+  where go s (c : cs) | Just cl <- closing c = go (cl : s) cs
+        go (c:s) (c':cs) | c == c' = go s cs
+        go _ (c:_) = SErr c
+        go s [] = Incomplete s
+
+main :: IO ()
+main = do
+    inp <- getInput 10
+    print $ sum [score1 c | SErr c <- map parse inp]
+    let middle l = sort l !! (length l `div` 2)
+    print $ middle [sum (zipWith (*) (reverse $ map score2 s) (iterate (*5) 1))
+                   | Incomplete s <- map parse inp]