1 files changed, 48 insertions, 0 deletions

diff --git a/execs/Day11.hs b/execs/Day11.hs
new file mode 100644
index 0000000..e2f138b
--- /dev/null
+++ b/execs/Day11.hs
@@ -0,0 +1,48 @@
+module Main where
+
+import Utils
+import Data.List (sortOn)
+import Data.Map (Map, (!))
+import qualified Data.Map as Map
+import Data.Maybe
+
+dirs = [ (-1,-1), (0,-1), (1,-1)
+       , (-1, 0),         (1, 0)
+       , (-1, 1), (0, 1), (1, 1)
+       ]
+
+adjs1 m pt = howMany (== '#') $ mapMaybe ((`Map.lookup` m) . add pt) dirs
+
+inGrid (x, y) w h = x < w && x >= 0 && y < h && y >= 0
+adjs2 grid pt w h = howMany ((== '#') . head)
+                        $ filter (not . null)
+                        $ map (dropWhile (== '.')
+                                . map (grid !)
+                                . takeWhile (inside (0, 0) (w-1, h-1))
+                                . map ($ pt)
+                                . repeatF
+                                . add)
+                     dirs
+
+rule1 w h m pt@(x, y) = if as == 0 then '#' else 'L'
+    where as = adjs2 m pt w h
+
+rule2 w h m pt@(x, y) = if as >= 5 then 'L' else '#'
+    where as = adjs2 m pt w h
+
+doStep w h m = Map.mapWithKey fn m
+    where fn k 'L' = rule1 w h m k
+          fn k '#' = rule2 w h m k
+          fn k '.' = '.'
+
+stepWhile prev w h
+  | prev == next = next
+  | otherwise = stepWhile next w h
+  where next = doStep w h prev
+
+main :: IO ()
+main = do
+    n <- readFile "input/11"
+    let (grid, width, height) = makeGrid n
+    let solve1 = stepWhile grid width height
+    print $ howMany ((== '#') . snd) $ Map.toList solve1