Day eleven

day-11-haskell/src/Lib.hs

@@ -0,0 +1,28 @@
+module Lib (task1, task2) where
+
+import Control.Monad (join)
+import Flow
+
+task1 :: String -> Int
+task1 input = parse input |> recurse blink 25 |> length
+
+task2 :: String -> Int
+task2 input = parse input |> recurse blink 75 |> length
+
+parse :: String -> [Int]
+parse input = words input |> map read
+
+recurse :: (a -> a) -> Int -> a -> a
+recurse fun count start = iterate fun start !! count
+
+blink :: [Int] -> [Int]
+blink stones = map blinkItem stones |> join
+
+blinkItem :: Int -> [Int]
+blinkItem 0 = [1]
+blinkItem number = let digits = show number |> map (read . pure) :: [Int]
+                   in if length digits `mod` 2 == 0
+                      then case splitAt (length digits `div` 2) digits of
+                        (first, second) -> [map show first |> join |> read, map show second |> join |> read]
+                      else [number * 2024]
+