1 files changed, 82 insertions, 0 deletions
diff --git a/day06/day06.hs b/day06/day06.hs
new file mode 100644
index 0000000..fa022f7
--- /dev/null
+++ b/day06/day06.hs
@@ -0,0 +1,82 @@
+import Data.List
+import Data.Maybe
+
+data Cell = Clr | Obs deriving (Show, Eq)
+type Grid = [[Cell]]
+type Coo = (Int, Int)
+data Dir = U | R | D | L deriving (Show, Eq)
+type Guard = (Coo, Dir)
+
+(!?) :: Grid -> Coo -> Maybe Cell
+grid !? (row, col)
+  | row < 0                     = Nothing
+  | row >= length grid          = Nothing
+  | col < 0                     = Nothing
+  | col >= (length $ head grid) = Nothing
+  | otherwise                   = Just (grid !! row !! col)
+
+findGuard :: Int -> [[Char]] -> Guard
+findGuard r (h:t)
+  | c == Nothing = findGuard (r + 1) t
+  | otherwise    = ((r, (fromJust c)), U)
+  where c = elemIndex '^' h
+
+consume :: [Char] -> (Grid, Guard)
+consume file =
+  let toCell = \ln -> case ln of
+                        '#' -> Obs
+                        otherwise -> Clr
+      grid = map (map toCell) (lines file)
+      guard = findGuard 0 (lines file) in
+        (grid, guard)
+
+step :: Grid -> Guard -> Maybe Guard
+step grid (coo@(r,c), U)
+  | cell == Nothing = Nothing
+  | cell == Just Obs = Just (coo, R)
+  | cell == Just Clr = Just (ncoo, U)
+  where
+    ncoo = (r - 1, c)
+    cell = grid !? ncoo
+step grid (coo@(r,c), R)
+  | cell == Nothing = Nothing
+  | cell == Just Obs = Just (coo, D)
+  | cell == Just Clr = Just (ncoo, R)
+  where
+    ncoo = (r, c + 1)
+    cell = grid !? ncoo
+step grid (coo@(r,c), D)
+  | cell == Nothing = Nothing
+  | cell == Just Obs = Just (coo, L)
+  | cell == Just Clr = Just (ncoo, D)
+  where
+    ncoo = (r + 1, c)
+    cell = grid !? ncoo
+step grid (coo@(r,c), L)
+  | cell == Nothing = Nothing
+  | cell == Just Obs = Just (coo, U)
+  | cell == Just Clr = Just (ncoo, L)
+  where
+    ncoo = (r, c - 1)
+    cell = grid !? ncoo
+
+(?:) :: Eq a => a -> [a] -> [a]
+el ?: arr
+  | el `elem` arr = arr
+  | otherwise = el:arr
+
+route :: Grid -> [Coo] -> Guard -> [Coo]
+route grid seen guard@(coo, dir)
+  | nguard == Nothing     = coo ?: seen
+  | otherwise = route grid (coo ?: seen) (fromJust nguard)
+  where
+    nguard = step grid guard
+
+part1 :: Grid -> Guard -> Int
+part1 grid guard = length $ route grid [] guard
+
+main = do
+  file <- readFile "day06.input"
+  let (grid, guard) = consume file
+  putStrLn ("Part 1: " ++ (show $ part1 grid guard))
+  --putStrLn ("Part 2: " ++ (show $ part2 lns))