Day 6

src/Days/D06.hs

@@ -0,0 +1,29 @@
+module Days.D06 (
+    day,
+) where
+
+import Common
+import Data.List (findIndex, nub, tails)
+
+distinct :: (Eq a) => [a] -> Bool
+distinct l = length l == length (nub l)
+
+windows :: Int -> [a] -> [[a]]
+windows n l
+    | length l < n = []
+    | otherwise = zipWith const (windowList l) [0 .. (length l - n)]
+  where
+    windowList :: [a] -> [[a]]
+    windowList = map (take n) . tails
+
+detector :: (Eq a) => Int -> [a] -> Maybe Int
+detector n = fmap (n +) . findIndex distinct . windows n
+
+part1 :: String -> Maybe Int
+part1 = detector 4
+
+part2 :: String -> Maybe Int
+part2 = detector 14
+
+day :: Day
+day = StringDay (\s -> Right (Answer <$> part1 s, Answer <$> part2 s))

src/Lib.hs

@@ -16,6 +16,7 @@ import Days.D02 qualified as D02
 import Days.D03 qualified as D03
 import Days.D04 qualified as D04
 import Days.D05 qualified as D05
+import Days.D06 qualified as D06
 
 import Data.Text.IO qualified as T
 
@@ -31,4 +32,5 @@ days =
     , [D03.day]
     , [D04.day]
     , [D05.day]
+    , [D06.day]
     ]