day 8

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

day08.hs

@@ -0,0 +1,44 @@
+import Data.Either (rights)
+import Data.Map qualified as M
+import Data.Text qualified as T
+import Lib (readFile')
+import Text.Parsec
+
+main :: IO ()
+main = do
+  (directionsRaw : _ : mapsRaw) <- T.lines <$> readFile' "day08.in"
+  let directions = cycle $ T.unpack directionsRaw
+  let maps' = rights $ map (parse parseMap "") mapsRaw
+  let maps = M.fromList maps'
+
+  putStr "Q1: "
+  print $ zzz directions maps 0 "AAA"
+
+  putStr "Q2: "
+  print . foldl1 lcm . map (xxz directions maps 0) . filter (\[_, _, c] -> c == 'A') . map fst $ maps'
+
+-- dumb and good recursion
+zzz :: String -> M.Map String (String, String) -> Int -> String -> Int
+zzz (d : ds) m acc str
+  | next == "ZZZ" = acc + 1
+  | otherwise = zzz ds m (acc + 1) next
+  where
+    Just (left, right) = M.lookup str m
+    next = if d == 'L' then left else right
+
+xxz :: String -> M.Map String (String, String) -> Int -> String -> Int
+xxz (d : ds) m acc str
+  | [_, _, 'Z'] <- next = acc + 1
+  | otherwise = xxz ds m (acc + 1) next
+  where
+    Just (left, right) = M.lookup str m
+    next = if d == 'L' then left else right
+
+-- Parsing --
+
+parseMap :: (Stream s m Char) => ParsecT s u m (String, (String, String))
+parseMap = do
+  a <- many1 letter <* string " = ("
+  b <- many1 letter <* string ", "
+  c <- many1 letter <* char ')'
+  return (a, (b, c))