Add 2020 day 19

haskellAoC/src/Y2020/Day19.hs

@@ -1,6 +1,49 @@
 module Y2020.Day19 (y20day19) where
 
+import qualified Data.IntMap as M
+import           Data.List.Split
+
+data Rule = AndRule Rule Rule |
+            OrRule Rule Rule |
+            RefRule Int |
+            CharRule Char deriving (Show)
+
+parseRule :: String -> (Int, Rule)
+parseRule input = (ruleId, rule)
+  where rule    = parseFn $ parts !! 1
+        ruleId  = read $ parts !! 0
+        parts   = splitOn ": " input
+        parseFn ['"', c, '"'] = CharRule c
+        parseFn str
+          | '|' `elem` str = OrRule (parseFn $ pipeSplit !! 0) (parseFn $ pipeSplit !! 1)
+          | ' ' `elem` str = AndRule (parseFn $ spaceSplit !! 0) (parseFn $ spaceSplit !! 1)
+          | otherwise      = RefRule (read str)
+          where spaceSplit = words str
+                pipeSplit  = splitOn " | " str
+
+matchRule :: M.IntMap Rule -> Int -> String -> Bool
+matchRule ruleset ruleId input = "" `elem` (fn rule0 input)
+  where rule0 = ruleset M.! ruleId
+        fn :: Rule -> String -> [String]
+        fn _ ""           = []
+        fn rule str@(h:t) =
+          case rule of
+            CharRule c -> if h == c
+                          then [t]
+                          else []
+            RefRule r     -> fn (ruleset M.! r) str
+            OrRule  r1 r2 -> (fn r1 str) ++ (fn r2 str)
+            AndRule r1 r2 -> [p2 | p1 <- fn r1 str, p2 <- fn r2 p1]
+
+
 y20day19 :: [String] -> (String, String)
-y20day19 input = (part1, part2)
-  where part1  = "WIP"
-        part2  = "WIP"
+y20day19 input  = (part1, part2)
+  where part1   = show $ length $ filter (matchRule rules 0) $ entries
+        part2   = show $ length $ filter (matchRule rulesP2 0) $ entries
+        input'  = splitOn [""] input
+        rules   = M.fromList $ map parseRule $ input' !! 0
+        entries = input' !! 1
+        rulesP2 = M.insert 8 (OrRule (RefRule 42) (AndRule (RefRule 42) (RefRule 8))) $
+                  M.insert 11 (OrRule (AndRule (RefRule 42) (RefRule 31))
+                               (AndRule (RefRule 42) (AndRule (RefRule 11) (RefRule 31)))) $
+                  rules