P1

Author: mnvr

19.hs

@@ -1,9 +1,9 @@
 import Data.Char (isDigit)
-import Data.List (elemIndex)
+import Data.List (elemIndex, find)
 import Data.Map qualified as M
 
 main :: IO ()
-main = interact $ (++ "\n") . show . parse
+main = interact $ (++ "\n") . show . p1 . parse
 
 type Workflows = M.Map String [Rule]
 type Rule = (Maybe Condition, String)
@@ -13,14 +13,14 @@ type Part = [Int]
 parse :: String -> (Workflows, [Part])
 parse = both . lines
   where
-    both s = let (a, b) = span (/= "") s in (workflows a, map part b)
+    both s = let (a, b) = span (/= "") s in (workflows a, map part (drop 1 b))
     workflows = M.fromList . map workflow
     workflow s = (rules . drop 1) <$> break (== '{') s
     rules [] = []
     rules s = let (a, b) = break (`elem` ",}") s in rule a : rules (drop 1 b)
     rule s = case break (== ':') s of
         (r, []) -> (Nothing, r)
-        (c, r) -> (Just (condition c), r)
+        (c, r) -> (Just (condition c), drop 1 r)
     condition (p:c:rs) = case p `elemIndex` "xmas" of
         Just i -> (i, c, read rs)
     part s = case reads (snd $ break isDigit s) of
@@ -32,3 +32,11 @@ valid ws p = go "in"
   where
     go "A" = True
     go "R" = False
+    go w = go $ next ((M.!) ws w)
+    next ((Nothing, r) : _) = r
+    next ((Just c, r) : rs) = if test c then r else next rs
+    test (i, '<', v) = (p !! i) < v
+    test (i, '>', v) = (p !! i) > v
+
+p1 :: (Workflows, [Part]) -> Int
+p1 (workflows, parts) = sum . concat $ filter (valid workflows) parts