day 6: init

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

aoc2025.cabal

@@ -55,3 +55,8 @@ executable day05
   hs-source-dirs: src
   main-is:        Day05.hs
   build-depends:  libaoc
+
+executable day06
+  import:         common
+  hs-source-dirs: src
+  main-is:        Day06.hs

flake.nix

@@ -45,7 +45,7 @@
               name = n: "day${(if n < 10 then "0" else "") + toString n}";
             in
             with pkgs.lib;
-            genAttrs (map name (range 1 5)) (n: {
+            genAttrs (map name (range 1 6)) (n: {
               type = "app";
               program = "${self'.packages.aoc2025}/bin/${n}";
             });

src/Day06.hs

@@ -0,0 +1,48 @@
+import Data.Bifunctor (Bifunctor (bimap))
+import Data.List (transpose)
+
+data Operation = Add | Multiply deriving (Show)
+
+type ProblemRaw = ([String], Operation)
+
+type Problem = ([Int], Operation)
+
+-- We are not going to use Parsec this time, so let's just group up the columns manually based on the
+-- operator's index then we can simply use transpose later for part2 as well
+
+parse :: String -> [ProblemRaw]
+parse raw =
+  let ls = lines raw
+      opLine = last ls
+      numLines = init ls
+
+      ops :: [(Operation, Int)]
+      ops =
+        [ (if c == '+' then Add else Multiply, i)
+        | (c, i) <- zip opLine [0 ..],
+          c /= ' '
+        ]
+
+      starts = map snd ops
+      slices line =
+        [ take (next - start - 1) (drop start line)
+        | (start, next) <- zip starts (drop 1 starts ++ [length line + 1])
+        ]
+   in zip (transpose (map slices numLines)) (map fst ops)
+
+solve :: [Problem] -> Int
+solve = sum . map solveProblem
+  where
+    solveProblem :: Problem -> Int
+    solveProblem (nums, Multiply) = product nums
+    solveProblem (nums, Add) = sum nums
+
+main :: IO ()
+main =
+  do
+    raw <- readFile "./inputs/day6.in"
+    let rawProblems = parse raw
+        problems1 = map (bimap (map read) id) rawProblems
+        problems2 = map (bimap (map read . transpose) id) rawProblems
+    putStr "Part 1: " >> print (solve $ problems1)
+    putStr "Part 2: " >> print (solve $ problems2)