day 11

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

aoc2024.cabal

@@ -11,6 +11,7 @@ common common
   default-extensions:
     LambdaCase
     ViewPatterns
+    TupleSections
 
   build-depends:
     , base    >=4.14 && <5
@@ -89,3 +90,9 @@ executable day10
   hs-source-dirs: src
   main-is:        Day10.hs
   build-depends:  containers
+
+executable day11
+  import:         common
+  hs-source-dirs: src
+  main-is:        Day11.hs
+  build-depends:  containers

src/Day11.hs

@@ -0,0 +1,30 @@
+module Main where
+
+import qualified Data.IntMap as IM
+
+blink :: Int -> [Int]
+blink 0 = [1]
+blink x
+  | (l, 0) <- len x `quotRem` 2,
+    (a, b) <- x `quotRem` (10 ^ l) =
+      [a, b]
+  | otherwise = [x * 2024]
+  where
+    len :: Int -> Int
+    len 0 = 0
+    len a = 1 + len (a `div` 10)
+
+blinkAll :: IM.IntMap Int -> IM.IntMap Int
+blinkAll xs = IM.fromListWith (+) [(x', c) | (x, c) <- IM.toList xs, x' <- blink x]
+
+blinkN :: Int -> IM.IntMap Int -> Int
+blinkN n = IM.foldr (+) 0 . (!! n) . iterate blinkAll
+
+main :: IO ()
+main =
+  do
+    raw <- map read . words <$> readFile "./inputs/day11.in"
+    let counts = IM.fromListWith (+) $ map (,1) raw
+
+    putStr "Part 1: " >> print (blinkN 25 counts)
+    putStr "Part 2: " >> print (blinkN 75 counts)