From 8031b0327a6d4485d638cc032df621417f07da0c Mon Sep 17 00:00:00 2001
From: Quinten Kock <quintenkock@gmail.com>
Date: Mon, 13 Dec 2021 01:11:17 +0100
Subject: [PATCH] rewrite to not keep track of path

---
 2021/day12.hs | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/2021/day12.hs b/2021/day12.hs
index 302f2f4..dd0984a 100644
--- a/2021/day12.hs
+++ b/2021/day12.hs
@@ -4,8 +4,10 @@ import Data.Map ( Map, fromList, unionWith, empty, (!) )
 import Data.List.Split (splitOn)
 import qualified Data.Char
 
-type Path = (String,String)
-type System = Map String [String]
+type Cave = String
+type Path = (Cave,Cave)
+type System = Map Cave [Cave]
+
 
 readPath :: String -> Path
 readPath s = (from,to) where [from,to] = splitOn "-" s
@@ -13,19 +15,17 @@ readPath s = (from,to) where [from,to] = splitOn "-" s
 addPath :: Path -> System -> System
 addPath (from,to) = unionWith (++) (Data.Map.fromList [(from,[to]), (to,[from])])
 
-isUpper :: String -> Bool
+isUpper :: Cave -> Bool
 isUpper = Data.Char.isUpper . head
 
-pathFinder :: System -> [String] -> HashSet String -> Int
-pathFinder _ [] _ = error "no starting point!"
-pathFinder sys p@("end":xs) _ = 1
-pathFinder sys p@(x:xs) visited = sum $ map (\next -> pathFinder sys (next:p) (next `insert` visited)) elig
+pathFinder :: System -> Cave -> HashSet Cave -> Int
+pathFinder sys "end" _ = 1
+pathFinder sys x visited = sum $ map (\next -> pathFinder sys next (next `insert` visited)) elig
     where elig = filter (\cave -> isUpper cave || not (cave `member` visited)) (sys ! x)
 
-pathFinder2 :: System -> [String] -> HashSet String -> Int
-pathFinder2 _ [] _ = error "no starting point!"
-pathFinder2 sys p@("end":xs) _ = 1
-pathFinder2 sys p@(x:xs) visited = sum $ map (\next -> f next sys (next:p) (next `insert` visited)) elig
+pathFinder2 :: System -> Cave -> HashSet Cave -> Int
+pathFinder2 sys "end" _ = 1
+pathFinder2 sys x visited = sum $ map (\next -> f next sys next (next `insert` visited)) elig
     where
         f cave = if isUpper cave || not (cave `member` visited) then pathFinder2 else pathFinder
         elig = filter (/= "start") (sys ! x)
@@ -36,7 +36,7 @@ main = do
     let system = foldr addPath Data.Map.empty input
 
     putStrLn "part 1: "
-    print $ pathFinder system ["start"] (Data.HashSet.fromList ["start"])
+    print $ pathFinder system "start" (Data.HashSet.fromList ["start"])
 
     putStrLn "part 2: "
-    print $ pathFinder2 system ["start"] (Data.HashSet.fromList ["start"])
+    print $ pathFinder2 system "start" (Data.HashSet.fromList ["start"])