Solve day 1

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "inputs/real"]
+	path = inputs/real
+	url = git@github.com:georgefst/aoc-private-inputs.git

aoc.cabal

@@ -9,6 +9,10 @@ executable aoc
     main-is: Main.hs
     hs-source-dirs: app
     default-language: GHC2024
+    default-extensions:
+        BlockArguments
+        MultiWayIf
+        ViewPatterns
     ghc-options:
         -Wall
     build-depends:

app/Main.hs

@@ -1,4 +1,40 @@
-module Main where
+module Main (main) where
+
+import Control.Monad.State
+import Data.Traversable
+import Text.Read (readMaybe)
 
 main :: IO ()
-main = putStrLn "Hello, Haskell!"
+main = do
+    Just input <-
+        traverse
+            ( \case
+                'L' : (readMaybe -> Just i) -> Just (L, Inc i)
+                'R' : (readMaybe -> Just i) -> Just (R, Inc i)
+                _ -> Nothing
+            )
+            . lines
+            <$> readFile "inputs/examples/1"
+    print
+        . sum
+        . flip evalState 50
+        $ for input \(d, i) -> state \p ->
+            let p' = step i d p
+             in (Count if p' == 0 then 1 else 0, p')
+
+data Direction = L | R
+    deriving (Eq, Ord, Show)
+
+newtype Pos = Pos Int
+    deriving newtype (Eq, Ord, Show, Num)
+
+newtype Inc = Inc Int
+    deriving newtype (Eq, Ord, Show, Num)
+
+newtype Count = Count Int
+    deriving newtype (Eq, Ord, Show, Num)
+
+step :: Inc -> Direction -> Pos -> Pos
+step (Inc i) d (Pos p) = Pos case d of
+    L -> (p - i) `mod` 100
+    R -> (p + i) `mod` 100

inputs/examples/1

@@ -0,0 +1,10 @@
+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82

inputs/real

@@ -0,0 +1 @@
+Subproject commit ab940388ba53f2fef932d09aeb44443e2a9407b7