70 lines
2.4 KiB
Haskell
70 lines
2.4 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Functor
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import qualified Data.List as L
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import qualified Data.Map as M
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import Data.Maybe
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import Data.Ord (comparing)
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import qualified Data.Set as S
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import Debug.Trace
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exampleExpectedOutput = 7
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type Computer = String
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type Link = (Computer, Computer)
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type Input = [Link]
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type Parser = Parsec Void String
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parseLink :: Parser Link
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parseLink = (,) <$> some letterChar <* char '-'
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<*> some letterChar
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parseInput' :: Parser Input
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parseInput' = some (parseLink <* eol) <* eof
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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type Network = M.Map Computer [Computer]
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type NetGroup = S.Set [Computer]
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compute :: Input -> Int
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compute links = length tgroups
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where
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tgroups :: [[Computer]]
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tgroups = L.nub $ L.filter (\(a:b:c:[]) -> and [isConnected a b, isConnected a c, isConnected b c]) $ L.sort $ map L.sort $ concatMap tgroup thosts
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tgroup :: Computer -> [[Computer]]
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tgroup c = map (\ns -> (c:ns)) $ tgroup' (network M.! c)
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tgroup' :: [Computer] -> [[Computer]]
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tgroup' (n:ns) = map (\c -> [n,c]) ns ++ tgroup' ns
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tgroup' _ = []
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isConnected :: Computer -> Computer -> Bool
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isConnected c1 c2 = L.elem c1 $ network M.! c2
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thosts :: [Computer]
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thosts = M.keys $ M.filterWithKey (\k _ -> head k == 't') network
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network = L.foldl' connect M.empty links
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connect :: Network -> Link -> Network
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connect net (c1, c2) = connectOne c1 c2 $ connectOne c2 c1 net
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connectOne :: Computer -> Computer -> Network -> Network
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connectOne c1 c2 net = case M.lookup c1 net of
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Just l -> M.insert c1 (c2:l) net
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Nothing -> M.insert c1 [c2] net
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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