Day 5

Day5/puzzle1.hs

@@ -0,0 +1,16 @@
+import Data.List.Split (splitOn)
+
+isSorted :: [(String, String)] -> [String] -> Bool
+isSorted rules [x] = True
+isSorted rules (x:xs) = let after = [ p | (p, n) <- rules, n == x ]
+                        in  not (any (`elem` after) xs) && isSorted rules xs
+
+getMiddle :: [String] -> String
+getMiddle xs = xs !! (length xs `div` 2)
+
+main = do
+    contents <- map (splitOn "|") . lines <$> readFile "day5.txt"
+    let rules = [ (x, y) | [x, y] <- takeWhile (/= [""]) contents ]
+        updates = concatMap (map (splitOn ",")) . tail $ dropWhile (/= [""]) contents
+        sorted = filter (isSorted rules) updates
+    print . sum $ map (read . getMiddle) sorted