solve 2024 day 11

2024/README.md

@@ -3,7 +3,7 @@
 |  S  |  M  |  T  |  W  |  T  |  F  |  S  |
 | :-: | :-: | :-: | :-: | :-: | :-: | :-: |
 | [1] | [2] | [3] | [4] | [5] | [6] | [7] |
-| [8] | [9] | [10]|  11 |  12 |  13 |  14 |
+| [8] | [9] | [10]| [11]|  12 |  13 |  14 |
 |  15 |  16 |  17 |  18 |  19 |  20 |  21 |
 |  22 |  23 |  24 |  25 |     |     |     |
 
@@ -17,3 +17,4 @@
 [8]: ./lib/2024/8.ex
 [9]: ./lib/2024/9.ex
 [10]: ./lib/2024/10.ex
+[11]: ./lib/2024/11.ex

2024/lib/2024/11.ex

@@ -0,0 +1,89 @@
+import AOC
+import AOC.Prelude
+
+aoc 2024, 11 do
+  require Integer
+
+  def p1(input) do
+    input
+    |> read_stones()
+    |> count_stones_after_blink(25)
+  end
+
+  def p2(input) do
+    input
+    |> read_stones()
+    |> count_stones_after_blink(75)
+  end
+
+  ##
+
+  defp count_stones_after_blink(stones, n) do
+    stones
+    |> Stream.iterate(&blink/1)
+    |> Enum.at(n)
+    |> count_stones()
+  end
+
+  defp blink(stones) do
+    for {stone, count} <- stones, reduce: stones do
+      stones ->
+        cond do
+          stone == 0 ->
+            stones
+            |> remove_stones(0, count)
+            |> add_stones(1, count)
+
+          even_digits?(stone) ->
+            {left, right} = split_stone(stone)
+
+            stones
+            |> remove_stones(stone, count)
+            |> add_stones(left, count)
+            |> add_stones(right, count)
+
+          true ->
+            stones
+            |> remove_stones(stone, count)
+            |> add_stones(stone * 2024, count)
+        end
+    end
+  end
+
+  defp even_digits?(num) do
+    num
+    |> Integer.digits()
+    |> Enum.count()
+    |> Integer.is_even()
+  end
+
+  defp split_stone(num) do
+    digits = Integer.digits(num)
+
+    {left, right} = Enum.split(digits, div(length(digits), 2))
+
+    {Integer.undigits(left), Integer.undigits(right)}
+  end
+
+  defp remove_stones(stones, num, count) do
+    Map.update(stones, num, 0, &(&1 - count))
+  end
+
+  defp add_stones(stones, num, count) do
+    Map.update(stones, num, count, &(&1 + count))
+  end
+
+  defp count_stones(stones) do
+    stones
+    |> Enum.map(&elem(&1, 1))
+    |> Enum.sum()
+  end
+
+  ## input
+
+  defp read_stones(input) do
+    input
+    |> ints()
+    |> Enum.frequencies()
+  end
+end

README.md

@@ -15,8 +15,8 @@
 | [2021] | **43/50** 🌟 | Elixir |
 | [2022] | **14/50** 🌟 | Elixir, Haskell |
 | [2023] | **19/50** 🌟 | Elixir, Haskell |
-| [2024] | **20/50** 🌟 | Elixir |
-| **Total** | **176** 🌟| |
+| [2024] | **22/50** 🌟 | Elixir |
+| **Total** | **178** 🌟| |
 
 [2015]: ./2015
 [2017]: ./2017