Day 3 Part 2

03/Main.idr

@@ -44,13 +44,32 @@ parseBackpack input =
 duplicatedItems : Backpack -> List Item
 duplicatedItems (B left right) = nub $ intersect left right
 
+-- Shared items across a collection of backpack
+shared : List Backpack -> List Item
+shared xs =
+  let combined = map (\(B left right) => left ++ right ) xs
+  in nub . intersectAll $ combined
+
+-- Chunk a list
+chunk : Nat -> List a -> List (List a)
+chunk x [] = []
+chunk x xs =
+  let head = take x xs
+      tail = chunk x . drop x $ xs
+  in head :: tail
+
 main : IO ()
 main =
   do file <- readFile "input"
      case file of
        Right content =>
         let backpacks = catMaybes . map parseBackpack . lines $ content
-            priorityTotals = foldl (+) 0 . map (foldl (+) 0 . map priority . duplicatedItems) $ backpacks
+            priorityTotals = sum . map (sum . map priority . duplicatedItems) $ backpacks
+            elves = chunk 3 backpacks
+            badges = map shared elves
+            badgeTotal = sum . map (sum . map priority) $ badges
         in do putStr "part 1: "
               printLn priorityTotals
+              putStr "part 2: "
+              printLn badgeTotal
        Left err => printLn err