2023 day 8: add Haskell solution

.gitignore

@@ -4,6 +4,7 @@
 *data*.txt
 [Mm]ain
 [Mm]ain-[0-9]
+[Mm]ain[0-9]
 
 # Nix stuff
 result*

2023/8/Main1.hs

@@ -0,0 +1,26 @@
+import qualified Data.HashMap.Strict as HMS
+
+type DataMap = HMS.HashMap String (String, String)
+
+getDirection :: Char -> (a, a) -> a
+getDirection 'L' = fst
+getDirection 'R' = snd
+
+countTimes :: String -> DataMap -> Int
+countTimes directions m = countTimes' directions "AAA" 0
+  where
+    countTimes' (d:ds) s
+      | s == "ZZZ" = id
+      | otherwise  = countTimes' ds (getDirection d $ m HMS.! s) . succ
+
+getDataMap :: [String] -> DataMap
+getDataMap = HMS.fromList . map parseLine
+  where
+    parseLine l = (take 3 l, (take 3 $ drop 7 l, take 3 $ drop 12 l))
+
+main :: IO ()
+main = do
+  allLines <- lines <$> readFile "data.txt"
+  let directions = cycle $ head allLines
+      dataMap = getDataMap $ drop 2 allLines
+  print $ countTimes directions dataMap

2023/8/Main2.hs

@@ -0,0 +1,31 @@
+import qualified Data.HashMap.Strict as HMS
+import Data.List (foldl1')
+
+type DataMap = HMS.HashMap String (String, String)
+
+getDirection :: Char -> (a, a) -> a
+getDirection 'L' = fst
+getDirection 'R' = snd
+
+countTimes :: String -> DataMap -> String -> Int
+countTimes directions m start = countTimes' directions start 0
+  where
+    countTimes' (d:ds) ss@(s:_)
+      | s == 'Z'  = id
+      | otherwise = countTimes' ds (getDirection d $ m HMS.! ss) . succ
+
+solve :: String -> DataMap -> Int
+solve directions m = foldl1' lcm $ map (countTimes directions m) $ filter ((== 'A') . head) $ HMS.keys m
+
+getDataMap :: [String] -> DataMap
+getDataMap = HMS.fromList . map parseLine
+  where
+    revTake3 = reverse . take 3
+    parseLine l = (revTake3 l, (revTake3 $ drop 7 l, revTake3 $ drop 12 l))
+
+main :: IO ()
+main = do
+  allLines <- lines <$> readFile "data.txt"
+  let directions = cycle $ head allLines
+      dataMap = getDataMap $ drop 2 allLines
+  print $ solve directions dataMap