From 6c37ffc703834884cb13bae873ba38d8f284d6ef Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Mon, 13 Dec 2021 21:02:20 +0100
Subject: 11

---
 2021/11.hs | 36 ++++++++++++++++++++++++++++--------
 2021/11.in | 10 ++++++++++
 2 files changed, 38 insertions(+), 8 deletions(-)
 create mode 100644 2021/11.in

diff --git a/2021/11.hs b/2021/11.hs
index cf23cec..ff01e17 100644
--- a/2021/11.hs
+++ b/2021/11.hs
@@ -1,15 +1,16 @@
-{-# OPTIONS -Wno-type-defaults #-}
+{-# LANGUAGE MultiWayIf #-}
 module Main where
 
 import qualified Data.Array as A
-import Data.List
-import Data.Maybe
+import Data.List (findIndex)
+import Data.Maybe (fromJust)
+import Data.Monoid (Sum(..))
 
 import Input
 
 
-stencil8 :: (a -> [a] -> b) -> a -> A.Array (Int, Int) a -> A.Array (Int, Int) b
-stencil8 f def arr =
+stencil8 :: a -> (a -> [a] -> b) -> A.Array (Int, Int) a -> A.Array (Int, Int) b
+stencil8 def f arr =
     A.listArray (A.bounds arr)
       [f (arr A.! (y, x))
          [get (yi, xi)
@@ -22,10 +23,29 @@ stencil8 f def arr =
                | otherwise = def
     ((y1, x1), (y2, x2)) = A.bounds arr
 
-step1 :: A.Array (Int, Int) Int -> A.Array (Int, Int) Int
-step1 = stencil _ 0
+amap :: A.Ix i => (a -> b) -> A.Array i a -> A.Array i b
+amap f a = A.listArray (A.bounds a) (map f (A.elems a))
+
+flash :: A.Array (Int, Int) Int -> A.Array (Int, Int) Int
+flash = stencil8 0 $ \v env -> if | v < 0 -> v
+                                  | v > 9 -> -1
+                                  | otherwise -> v + sum (map (fromEnum . (>9)) env)
+
+step :: A.Array (Int, Int) Int -> (Sum Int, A.Array (Int, Int) Int)
+step a =
+    let a' = fixpoint flash (amap (+1) a)
+    in (Sum (length [() | -1 <- A.elems a']), amap (\v -> if v < 0 then 0 else v) a')
+  where fixpoint f x = let y = f x in if y == x then x else fixpoint f y
+
+display :: A.Array (Int, Int) Int -> String
+display arr = unlines
+    [concat [show (arr A.! (y, x)) | x <- [x1..x2]] | y <- [y1..y2]]
+  where ((y1, x1), (y2, x2)) = A.bounds arr
 
 main :: IO ()
 main = do
     inp <- getInput 11
-    return ()
+    let arr0 = A.listArray ((1, 1), (length inp, length (head inp))) (concatMap (map (read . pure)) inp)
+    let states = iterate (>>= step) (return arr0)
+    print (getSum (fst (states !! 100)))
+    print (fromJust $ findIndex (all (== 0) . A.elems) (map snd states))
diff --git a/2021/11.in b/2021/11.in
new file mode 100644
index 0000000..07abafe
--- /dev/null
+++ b/2021/11.in
@@ -0,0 +1,10 @@
+3322874652
+5636588857
+7755117548
+5854121833
+2856682477
+3124873812
+1541372254
+8634383236
+2424323348
+2265635842
-- 
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