From 4dd247c0e10c8d1c8466ff16fed1daa282bf9e5e Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Mon, 6 Dec 2021 21:58:10 +0100
Subject: 6

---
 2021/6.hs    | 20 ++++++++++++++++++++
 2021/6.in    |  1 +
 2021/Util.hs |  3 ++-
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 2021/6.hs
 create mode 100644 2021/6.in

diff --git a/2021/6.hs b/2021/6.hs
new file mode 100644
index 0000000..90fe324
--- /dev/null
+++ b/2021/6.hs
@@ -0,0 +1,20 @@
+module Main where
+
+import qualified Data.Array as A
+import Numeric.Natural
+
+import Input
+import Util
+
+
+main :: IO ()
+main = do
+    inp <- map read . toList . splitOn (== ',') . head <$> getInput 6
+    let evolve :: A.Array Int Natural -> A.Array Int Natural
+        evolve arr = A.accumArray (+) 0 (0, 8) $
+            [(8, arr A.! 0), (6, arr A.! 0)] ++
+            [(i, arr A.! (i + 1)) | i <- [0..7]]
+        initState = A.accumArray (+) 0 (0, 8) [(i, 1) | i <- inp]
+        after n = sum (A.elems (iterate evolve initState !! n))
+    print (after 80)
+    print (after 256)
diff --git a/2021/6.in b/2021/6.in
new file mode 100644
index 0000000..70f9ad7
--- /dev/null
+++ b/2021/6.in
@@ -0,0 +1 @@
+1,4,3,3,1,3,1,1,1,2,1,1,1,4,4,1,5,5,3,1,3,5,2,1,5,2,4,1,4,5,4,1,5,1,5,5,1,1,1,4,1,5,1,1,1,1,1,4,1,2,5,1,4,1,2,1,1,5,1,1,1,1,4,1,5,1,1,2,1,4,5,1,2,1,2,2,1,1,1,1,1,5,5,3,1,1,1,1,1,4,2,4,1,2,1,4,2,3,1,4,5,3,3,2,1,1,5,4,1,1,1,2,1,1,5,4,5,1,3,1,1,1,1,1,1,2,1,3,1,2,1,1,1,1,1,1,1,2,1,1,1,1,2,1,1,1,1,1,1,4,5,1,3,1,4,4,2,3,4,1,1,1,5,1,1,1,4,1,5,4,3,1,5,1,1,1,1,1,5,4,1,1,1,4,3,1,3,3,1,3,2,1,1,3,1,1,4,5,1,1,1,1,1,3,1,4,1,3,1,5,4,5,1,1,5,1,1,4,1,1,1,3,1,1,4,2,3,1,1,1,1,2,4,1,1,1,1,1,2,3,1,5,5,1,4,1,1,1,1,3,3,1,4,1,2,1,3,1,1,1,3,2,2,1,5,1,1,3,2,1,1,5,1,1,1,1,1,1,1,1,1,1,2,5,1,1,1,1,3,1,1,1,1,1,1,1,1,5,5,1
diff --git a/2021/Util.hs b/2021/Util.hs
index 7cd674d..f1e6046 100644
--- a/2021/Util.hs
+++ b/2021/Util.hs
@@ -1,5 +1,6 @@
-module Util where
+module Util (module Util, toList) where
 
+import Data.Foldable (toList)
 import Data.List
 import Data.List.NonEmpty (NonEmpty(..), (<|))
 
-- 
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