From 7f8ce383f9c82eecc36791174bf8fc614cdcf56d Mon Sep 17 00:00:00 2001
From: Quinten Kock <quintenkock@gmail.com>
Date: Mon, 13 Dec 2021 02:32:00 +0100
Subject: [PATCH] use bitsets

---
 2021/day12.hs | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/2021/day12.hs b/2021/day12.hs
index b5c5399..d2f4e69 100644
--- a/2021/day12.hs
+++ b/2021/day12.hs
@@ -2,7 +2,7 @@ module Day12 where
 -- import Data.HashSet (HashSet, member, insert, fromList)
 -- import Data.Map ( Map, fromList, unionWith, empty, (!), insert, elems) qualified (map)
 import qualified Data.Map as M
-import qualified Data.Bits
+import Data.Bits ( Bits(shiftL, (.|.), (.&.)) )
 
 import Data.HashSet (HashSet)
 import qualified Data.HashSet as S
@@ -23,16 +23,19 @@ addPath (from,to) = M.unionWith (++) (M.fromList [(from,[to]), (to,[from])])
 isUpper :: Cave -> Bool
 isUpper x = x < 0
 
-pathFinder :: System -> Cave -> HashSet Cave -> Int
+pathFinder :: System -> Cave -> Int -> Int
 pathFinder sys (-1) _ = 1
-pathFinder sys x visited = sum $ map (\next -> pathFinder sys next (next `S.insert` visited)) elig
-    where elig = filter (\cave -> isUpper cave || not (cave `S.member` visited)) (sys M.! x)
-
-pathFinder2 :: System -> Cave -> HashSet Cave -> Int
-pathFinder2 sys (-1) _ = 1
-pathFinder2 sys x visited = sum $ map (\next -> f next sys next (next `S.insert` visited)) elig
+pathFinder sys x visited = sum $ map (\next -> pathFinder sys next (nextmap next)) elig
     where
-        f cave = if isUpper cave || not (cave `S.member` visited) then pathFinder2 else pathFinder
+        nextmap next = if not (isUpper next) then next .|. visited else visited
+        elig = filter (\cave -> isUpper cave || (cave .&. visited) == 0) (sys M.! x)
+
+pathFinder2 :: System -> Cave -> Int -> Int
+pathFinder2 sys (-1) _ = 1
+pathFinder2 sys x visited = sum $ map (\next -> f next sys next (nextmap next)) elig
+    where
+        nextmap next = if not (isUpper next) then next .|. visited else visited
+        f cave = if isUpper cave || (cave .&. visited) == 0 then pathFinder2 else pathFinder
         elig = filter (/= 1) (sys M.! x)
 
 convert :: [String] -> M.Map String Int
@@ -53,7 +56,7 @@ main = do
     let integralSystem = M.mapKeys (conversion M.!) $ M.map (map (conversion M.!)) system
 
     putStrLn "part 1: "
-    print $ pathFinder integralSystem 1 (S.fromList [1])
+    print $ pathFinder integralSystem 1 1
 
     putStrLn "part 2: "
-    print $ pathFinder2 integralSystem 1 (S.fromList [1])
+    print $ pathFinder2 integralSystem 1 1