2024-23 part 1 in haskell

2024/23-LAN_Party/example

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+kh-tc
+qp-kh
+de-cg
+ka-co
+yn-aq
+qp-ub
+cg-tb
+vc-aq
+tb-ka
+wh-tc
+yn-cg
+kh-ub
+ta-co
+de-co
+tc-td
+tb-wq
+wh-td
+ta-ka
+td-qp
+aq-cg
+wq-ub
+ub-vc
+de-ta
+wq-aq
+wq-vc
+wh-yn
+ka-de
+kh-ta
+co-tc
+wh-qp
+tb-vc
+td-yn

2024/23-LAN_Party/first.hs

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