day6 part one

aoc2024.cabal

@@ -25,12 +25,13 @@ source-repository head
 
 library
   exposed-modules:
+      Data.Matrix
       Day1
       Day2
       Day3
       Day4
-      Day4.Matrix
       Day5
+      Day6
   other-modules:
       Paths_aoc2024
   autogen-modules:

input/day6.txt

@@ -0,0 +1,130 @@
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src/Data/Matrix.hs

@@ -1,10 +1,12 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
-module Day4.Matrix
+module Data.Matrix
   ( Matrix,
+    Position,
     buildMatrix,
     groupWith,
+    lookupValue,
     lookup,
     lookupMultiple,
     filterWithKey,
@@ -13,6 +15,7 @@ module Day4.Matrix
 where
 
 import qualified Data.IntMap.Lazy as IntMap
+import Data.List (find)
 import Data.Map.Lazy (Map)
 import qualified Data.Map.Lazy as Map
 import Data.Maybe
@@ -20,6 +23,8 @@ import Prelude hiding (lookup)
 
 newtype Matrix v = Matrix (Map (Int, Int) v)
 
+type Position = (Int, Int)
+
 buildMatrix :: [[a]] -> Matrix a
 buildMatrix xs = Matrix (go xs 0 Map.empty)
   where
@@ -36,21 +41,31 @@ buildMatrix xs = Matrix (go xs 0 Map.empty)
 size :: Matrix v -> Int
 size (Matrix hmap) = Map.size hmap
 
-filterWithKey :: ((Int, Int) -> v -> Bool) -> Matrix v -> Matrix v
+filterWithKey :: (Position -> v -> Bool) -> Matrix v -> Matrix v
 filterWithKey f (Matrix hmap) = Matrix (Map.filterWithKey f hmap)
 
-lookup :: (Int, Int) -> Matrix v -> Maybe v
+lookup :: Position -> Matrix v -> Maybe v
 lookup position (Matrix hmap) = Map.lookup position hmap
 
-lookupMultiple :: [(Int, Int)] -> Matrix v -> [v]
+lookupMultiple :: [Position] -> Matrix v -> [v]
 lookupMultiple positions matrix = mapMaybe (`lookup` matrix) positions
 
+{--
+  Search for the given value on the matrix.
+  Return the position of the first match if found and nothing if it doens't exist.
+--}
+lookupValue :: (Eq v) => v -> Matrix v -> Maybe Position
+lookupValue v (Matrix hmap) =
+  let entries = Map.toAscList hmap
+      mEntry = find ((== v) . snd) entries
+   in fst <$> mEntry
+
 {--
 Given a matrix of elements and a function mapping a position into an aggregation of its values,
 group the elements by the aggregation result.
 The values are grouped in order.
 --}
-groupWith :: forall v. ((Int, Int) -> Int) -> Matrix v -> [[v]]
+groupWith :: forall v. (Position -> Int) -> Matrix v -> [[v]]
 groupWith f (Matrix hmap) =
   let sortedEntries = Map.toAscList hmap
       intMap = foldr (\(position, value) -> insertValue (f position) value) IntMap.empty sortedEntries

src/Day4.hs

@@ -1,7 +1,7 @@
 module Day4 (partOne, partTwo) where
 
 import Data.List (sort, transpose)
-import qualified Day4.Matrix as M
+import qualified Data.Matrix as M
 
 partOne :: String -> Int
 partOne input =

src/Day6.hs

@@ -0,0 +1,81 @@
+module Day6 (partOne, partTwo) where
+
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as HashSet
+import Data.Matrix (Matrix, Position)
+import qualified Data.Matrix as M
+import Data.Maybe
+import Prelude hiding (Left, Right)
+
+data Error = StartingPositionNotFound
+  deriving (Show)
+
+partOne :: String -> Maybe Int
+partOne input = length <$> predictGuardsRoute (parseLabMap input)
+
+partTwo :: String -> Int
+partTwo _input = 0
+
+-- Laboratory Map
+--
+type LabMap = Matrix Char
+
+type Direction = Char
+
+type Guard = (Position, Direction)
+
+type Visited = HashSet (Position, Direction)
+
+parseLabMap :: String -> LabMap
+parseLabMap = M.buildMatrix . lines
+
+findGuard :: LabMap -> Maybe Guard
+findGuard matrix =
+  let mUp = M.lookupValue '^' matrix
+      mDown = M.lookupValue 'v' matrix
+      mRight = M.lookupValue '>' matrix
+      mLeft = M.lookupValue '<' matrix
+   in case [mUp, mDown, mRight, mLeft] of
+        [Just pos, _, _, _] -> Just (pos, '^')
+        [_, Just pos, _, _] -> Just (pos, 'v')
+        [_, _, Just pos, _] -> Just (pos, '>')
+        [_, _, _, Just pos] -> Just (pos, '<')
+        _ -> Nothing
+
+predictGuardsRoute :: LabMap -> Maybe [Position]
+predictGuardsRoute labMap = do
+  guard <- findGuard labMap
+  return (go guard HashSet.empty HashSet.empty)
+  where
+    go :: Guard -> Visited -> HashSet Position -> [Position]
+    go guard@(position, _) visited acc =
+      let guard' = moveGuard guard
+          acc' = HashSet.insert position acc
+          visited' = HashSet.insert guard visited
+       in -- If we have hit a loop or if the guard can't move anymore, finish prediction
+          if HashSet.member guard visited || guard == guard'
+            then HashSet.toList acc'
+            else go guard' visited' acc'
+
+    moveGuard :: Guard -> Guard
+    moveGuard guard =
+      let guard'@(position', _) = moveForward guard
+          mObstacle = M.lookup position' labMap
+       in case mObstacle of
+            Nothing -> guard
+            Just '#' -> turnRight guard
+            Just _ -> guard'
+
+    moveForward :: Guard -> Guard
+    moveForward ((row, col), '^') = ((row - 1, col), '^')
+    moveForward ((row, col), 'v') = ((row + 1, col), 'v')
+    moveForward ((row, col), '>') = ((row, col + 1), '>')
+    moveForward ((row, col), '<') = ((row, col - 1), '<')
+    moveForward guard = guard
+
+    turnRight :: Guard -> Guard
+    turnRight (pos, '^') = (pos, '>')
+    turnRight (pos, '>') = (pos, 'v')
+    turnRight (pos, 'v') = (pos, '<')
+    turnRight (pos, '<') = (pos, '^')
+    turnRight guard = guard