Day 11: Plutonian Pebbles

README.md

@@ -15,3 +15,4 @@ Development occurs in language-specific directories:
 |[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|[day8.py](py/aoc2024/day8.py)|[day8.rs](rs/src/day8.rs)|
 |[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day9.kt)|[day9.py](py/aoc2024/day9.py)|[day9.rs](rs/src/day9.rs)|
 |[Day10.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day10.kt)|[day10.py](py/aoc2024/day10.py)|[day10.rs](rs/src/day10.rs)|
+|[Day11.hs](hs/src/Day11.hs)||||

hs/aoc2024.cabal

@@ -23,6 +23,7 @@ library
   exposed-modules:
     Day1
     Day10
+    Day11
     Day2
     Day3
     Day4
@@ -71,6 +72,7 @@ test-suite aoc2024-test
   main-is: Main.hs
   other-modules:
     Day10Spec
+    Day11Spec
     Day1Spec
     Day2Spec
     Day3Spec

hs/app/Main.hs

@@ -9,6 +9,7 @@ import Data.Text (Text)
 import Data.Text.IO qualified as TIO (readFile)
 import Day1 qualified (part1, part2)
 import Day10 qualified (part1, part2)
+import Day11 qualified (part1, part2)
 import Day2 qualified (part1, part2)
 import Day3 qualified (part1, part2)
 import Day4 qualified (part1, part2)
@@ -50,3 +51,4 @@ main = do
   run 8 print [Day8.part1, Day8.part2]
   run 9 print [Day9.part1, Day9.part2]
   run 10 print [Day10.part1, Day10.part2]
+  run 11 (either fail print) [Day11.part1, Day11.part2]

hs/bench/Main.hs

@@ -8,6 +8,7 @@ import Data.Text (Text)
 import Data.Text.IO qualified as TIO (readFile)
 import Day1 qualified (part1, part2)
 import Day10 qualified (part1, part2)
+import Day11 qualified (part1, part2)
 import Day2 qualified (part1, part2)
 import Day3 qualified (part1, part2)
 import Day4 qualified (part1, part2)
@@ -92,5 +93,11 @@ main =
           "Day 10"
           [ bench "part 1" $ nf Day10.part1 input,
             bench "part 2" $ nf Day10.part2 input
+          ],
+      env (getDayInput 11) $ \input ->
+        bgroup
+          "Day 11"
+          [ bench "part 1" $ nf Day11.part1 input,
+            bench "part 2" $ nf Day11.part2 input
           ]
     ]

hs/src/Day11.hs

@@ -0,0 +1,31 @@
+{-# LANGUAGE MultiWayIf #-}
+
+-- |
+-- Module:         Day11
+-- Description:    <https://adventofcode.com/2024/day/11 Day 11: Plutonian Pebbles>
+module Day11 (part1, part2, solve) where
+
+import Common (readEntire)
+import Data.IntMap (IntMap)
+import Data.IntMap qualified as IntMap (toList)
+import Data.IntMap.Strict qualified as IntMap (fromListWith)
+import Data.Text (Text)
+import Data.Text qualified as T (words)
+import Data.Text.Read qualified as T (decimal)
+
+part1, part2 :: Text -> Either String Int
+part1 = solve 25
+part2 = solve 75
+
+solve :: Int -> Text -> Either String Int
+solve n input = do
+  nums <- mapM (readEntire T.decimal) $ T.words input
+  pure $ foldl' (+) 0 $ iterate step (IntMap.fromListWith (+) $ (,1) <$> nums) !! n
+
+step :: IntMap Int -> IntMap Int
+step counts = IntMap.fromListWith (+) $ do
+  (x, n) <- IntMap.toList counts
+  if
+    | x == 0 -> [(1, n)]
+    | s <- show x, (l, 0) <- length s `divMod` 2, (a, b) <- splitAt l s -> [(read a, n), (read b, n)]
+    | otherwise -> [(2024 * x, n)]

hs/test/Day11Spec.hs

@@ -0,0 +1,19 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Day11Spec (spec) where
+
+import Data.Text (Text)
+import Day11 (solve)
+import Test.Hspec (Spec, describe, it, shouldBe)
+
+example1, example2 :: Text
+example1 = "0 1 10 99 999\n"
+example2 = "125 17\n"
+
+spec :: Spec
+spec = do
+  describe "part 1" $ do
+    it "examples" $ do
+      solve 1 example1 `shouldBe` Right 7
+      solve 6 example2 `shouldBe` Right 22
+      solve 25 example2 `shouldBe` Right 55312