1 files changed, 4 insertions(+), 3 deletions(-)

M 2023/08b.hs

@@ 6,6 6,7 @@
 module Main where
 
 import Qulude
+import Qulude.Prime ( factorize )
 
 --import Data.Array ( (!) )
 import qualified Data.Array as Array


@@ 65,14 66,14 @@ findPrefixAndCycle w = let (i, vs) = f [] Map.empty w in
             Nothing -> f (w:acc) (Map.insert w i vs) ws
 
 analyze (p, cs) = case (f p, f cs) of
-                    ((l, []), (c, e:[])) -> if e + l == c then (l, c, e) else undefined
+                    ((p, []), (c, e:[])) -> if p + e == c then (p, c, e) else undefined
   where f w = (length w, List.findIndices isEnd w)
 
-partB (is, map) = fmap f starts
+partB (is, map) = foldl (*) 1 $ foldl List.union [] $ fmap factorize $ fmap (\(_, c, _) -> c) $ fmap f starts
   where starts = filter isStart $ Map.keys map
         f s = analyze $ findPrefixAndCycle $ walk map is s
 
 main :: IO ()
 main = with parser $ do
   --run "08b.example" "b example" partB -- 6
-  run "08.input" "b input" partB
+  run "08.input" "b input" partB -- 21003205388413