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do not enumerate paths; only count

This commit is contained in:
Quinten Kock 2021-12-13 01:07:08 +01:00
parent a8404b5872
commit 7c4c119eff
1 changed files with 8 additions and 10 deletions
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18
2021/day12.hs
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@ -16,16 +16,16 @@ addPath (from,to) = unionWith (++) (Data.Map.fromList [(from,[to]), (to,[from])]
isUpper :: String -> Bool
isUpper = Data.Char.isUpper . head
pathFinder :: System -> [String] -> HashSet String -> [[String]]
pathFinder :: System -> [String] -> HashSet String -> Int
pathFinder _ [] _ = error "no starting point!"
pathFinder sys p@("end":xs) _ = [p]
pathFinder sys p@(x:xs) visited = concatMap (\next -> pathFinder sys (next:p) (next `insert` visited)) elig
pathFinder sys p@("end":xs) _ = 1
pathFinder sys p@(x:xs) visited = sum $ map (\next -> pathFinder sys (next:p) (next `insert` visited)) elig
where elig = filter (\cave -> isUpper cave || not (cave `member` visited)) (sys ! x)
pathFinder2 :: System -> [String] -> HashSet String -> [[String]]
pathFinder2 :: System -> [String] -> HashSet String -> Int
pathFinder2 _ [] _ = error "no starting point!"
pathFinder2 sys p@("end":xs) _ = [p]
pathFinder2 sys p@(x:xs) visited = concatMap (\next -> f next sys (next:p) (next `insert` visited)) elig
pathFinder2 sys p@("end":xs) _ = 1
pathFinder2 sys p@(x:xs) visited = sum $ map (\next -> f next sys (next:p) (next `insert` visited)) elig
where
f cave = if isUpper cave || not (cave `member` visited) then pathFinder2 else pathFinder
elig = filter (/= "start") (sys ! x)
@ -36,9 +36,7 @@ main = do
let system = foldr addPath Data.Map.empty input
putStrLn "part 1: "
let paths = map reverse $ pathFinder system ["start"] (Data.HashSet.fromList ["start"])
print $ length paths
print $ pathFinder system ["start"] (Data.HashSet.fromList ["start"])
putStrLn "part 2: "
let paths = map reverse $ pathFinder2 system ["start"] (Data.HashSet.fromList ["start"])
print $ length paths
print $ pathFinder2 system ["start"] (Data.HashSet.fromList ["start"])