solve 2024 day 14

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 |     |     |     |
 
@@ -20,3 +20,4 @@
 [11]: ./lib/2024/11.ex
 [12]: ./lib/2024/12.ex
 [13]: ./lib/2024/13.ex
+[14]: ./lib/2024/14.ex

2024/lib/2024/14.ex

@@ -0,0 +1,96 @@
+import AOC
+
+aoc 2024, 14 do
+  # @bounds {11, 7}
+  @bounds {101, 103}
+
+  def p1(input) do
+    input
+    |> read_robots()
+    |> Stream.iterate(fn robots ->
+      Enum.map(robots, &move_robot(&1, @bounds))
+    end)
+    |> Enum.at(100)
+    |> Enum.map(&elem(&1, 0))
+    |> Enum.frequencies_by(&quadrant(&1, @bounds))
+    |> Map.delete(-1)
+    |> Map.values()
+    |> Enum.product()
+  end
+
+  def p2(input) do
+    input
+    |> read_robots()
+    |> Stream.iterate(fn robots ->
+      Enum.map(robots, &move_robot(&1, @bounds))
+    end)
+    |> Stream.with_index()
+    # noticed convergence every 101 seconds
+    |> Stream.take_every(101)
+    |> Enum.each(fn {robots, n} ->
+      IO.puts("")
+      IO.puts("------------------ Seconds elapsed: #{n} ------------------")
+      IO.puts("")
+
+      robots
+      |> Enum.frequencies_by(&elem(&1, 0))
+      |> render(@bounds)
+
+      IO.gets("Continue?")
+    end)
+  end
+
+  defp move_robot({{x, y}, {vx, vy} = velocity}, {max_x, max_y}) do
+    x_next = wrap_value(x + vx, max_x)
+    y_next = wrap_value(y + vy, max_y)
+
+    {{x_next, y_next}, velocity}
+  end
+
+  defp wrap_value(v, max) do
+    if v < 0 do
+      max + v
+    else
+      rem(v, max)
+    end
+  end
+
+  defp quadrant({x, y}, {max_x, max_y}) do
+    half_x = div(max_x, 2)
+    half_y = div(max_y, 2)
+
+    case {x < half_x, y < half_y, half_x == x or half_y == y} do
+      # special grouping on the lines bisecting that plane
+      {_, _, true} -> -1
+      # bin into quadrants
+      {true, true, _} -> 0
+      {false, true, _} -> 1
+      {true, false, _} -> 2
+      {false, false, _} -> 3
+    end
+  end
+
+  defp render(robots, {max_x, max_y}) do
+    for y <- 0..max_y do
+      line =
+        for x <- 0..max_x, into: "" do
+          "#{Map.get(robots, {x, y}, " ")}"
+        end
+
+      IO.puts(line)
+    end
+
+    robots
+  end
+
+  ## input
+
+  defp read_robots(input) do
+    ~r/p=(\d+),(\d+) v=(-?\d+),(-?\d+)/
+    |> Regex.scan(input, capture: :all_but_first)
+    |> Enum.map(fn nums ->
+      [px, py, vx, vy] = Enum.map(nums, &String.to_integer/1)
+      {{px, py}, {vx, vy}}
+    end)
+  end
+end

README.md

@@ -15,8 +15,8 @@
 | [2021] | **43/50** 🌟 | Elixir |
 | [2022] | **14/50** 🌟 | Elixir, Haskell |
 | [2023] | **19/50** 🌟 | Elixir, Haskell |
-| [2024] | **26/50** 🌟 | Elixir |
+| [2024] | **28/50** 🌟 | Elixir |
-| **Total** | **182** 🌟| |
+| **Total** | **184** 🌟| |
 
 [2015]: ./2015
 [2017]: ./2017