Day 11, that took me forever

day11/main.exs

@@ -0,0 +1,59 @@
+defmodule Day11 do
+  def run do
+    stones =
+      File.read!("data.txt")
+      |> String.trim()
+      |> String.split(" ")
+      |> Enum.map(&String.to_integer/1)
+
+    total = 75
+
+    part1 =
+      Enum.reduce(stones, %{stones: 0, map: %{}}, fn stone, acc ->
+        {new_stones, new_map} = processStoneCounts(stone, total, acc.map)
+        %{stones: acc.stones + new_stones, map: new_map}
+      end)
+
+    dbg(part1)
+  end
+
+  defp processStoneCounts(stone, steps_left, map) do
+    if steps_left == 0 do
+      {1, map}
+    else
+      key = {steps_left, stone}
+
+      if Map.has_key?(map, key) do
+        {Map.get(map, key), map}
+      else
+        length = Integer.digits(stone) |> length
+
+        new_stones2 =
+          case stone do
+            0 ->
+              [1]
+
+            s when rem(length, 2) == 0 ->
+              Integer.digits(s)
+              |> Enum.split(trunc(length / 2))
+              |> Tuple.to_list()
+              |> Enum.map(&Integer.undigits/1)
+
+            s ->
+              [s * 2024]
+          end
+
+        if length(new_stones2) == 2 do
+          {left, map2} = processStoneCounts(hd(new_stones2), steps_left - 1, map)
+          {right, map3} = processStoneCounts(Enum.at(new_stones2, 1), steps_left - 1, map2)
+          {left + right, Map.put(map3, key, left + right)}
+        else
+          {new, map2} = processStoneCounts(hd(new_stones2), steps_left - 1, map)
+          {new, Map.put(map2, key, new)}
+        end
+      end
+    end
+  end
+end
+
+Day11.run()