Day 14. There is probably a much smarter way to solve part 2 but I couldn\'t think of it

day14/main.exs

@@ -0,0 +1,88 @@
+# 94154500 too low
+
+defmodule Day14 do
+  def run do
+    robots =
+      File.read!("data.txt")
+      |> String.trim()
+      |> String.split("\n")
+      |> Enum.map(&parse_robot/1)
+
+    width = 101
+    height = 103
+    steps = 100
+
+    new_robots =
+      Enum.reduce(1..steps, robots, fn idx, acc ->
+        step(acc, {width, height})
+      end)
+
+    quads = [
+      Enum.filter(new_robots, fn r -> r.p.x < trunc(width / 2) and r.p.y < trunc(height / 2) end),
+      Enum.filter(new_robots, fn r -> r.p.x > trunc(width / 2) and r.p.y < trunc(height / 2) end),
+      Enum.filter(new_robots, fn r -> r.p.x < trunc(width / 2) and r.p.y > trunc(height / 2) end),
+      Enum.filter(new_robots, fn r -> r.p.x > trunc(width / 2) and r.p.y > trunc(height / 2) end)
+    ]
+
+    part1 = Enum.map(quads, &length/1) |> Enum.reduce(1, &*/2)
+    dbg(part1)
+
+    # part 2, print until i guess i see a tree
+    Enum.reduce(1..100_000, robots, fn idx, acc ->
+      IO.puts(idx)
+
+      res = step(acc, {width, height})
+
+      # ok only print if we see something interesting like an empty corner?
+      if corner_block(res) do
+        render(res, {width, height})
+      end
+
+      res
+    end)
+  end
+
+  defp corner_block(robots) do
+    Enum.all?(0..10, fn col ->
+      Enum.all?(0..10, fn row ->
+        rs = Enum.filter(robots, fn %{p: %{x: x, y: y}} -> x == col and y == row end)
+        length(rs) == 0
+      end)
+    end)
+  end
+
+  defp render(robots, {width, height}) do
+    Enum.each(0..(height - 1), fn row ->
+      Enum.each(0..(width - 1), fn col ->
+        r = Enum.filter(robots, fn %{p: %{x: x, y: y}} -> x == col and y == row end) |> length
+        if r == 0, do: IO.write("."), else: IO.write(r)
+      end)
+
+      IO.write("\n")
+    end)
+
+    IO.write("\n\n\n\n\n")
+    Process.sleep(300)
+    IO.puts(IO.ANSI.clear())
+
+    robots
+  end
+
+  defp step(robots, {width, height}) do
+    Enum.map(robots, fn %{p: p, v: v} ->
+      x = Integer.mod(p.x + v.x, width)
+      y = Integer.mod(p.y + v.y, height)
+      %{p: %{x: x, y: y}, v: v}
+    end)
+  end
+
+  defp parse_robot(str) do
+    ~r/p=(.+),(.+) v=(.+),(.+)/
+    |> Regex.run(str)
+    |> tl()
+    |> Enum.map(&String.to_integer/1)
+    |> (fn [a, b, c, d] -> %{p: %{x: a, y: b}, v: %{x: c, y: d}} end).()
+  end
+end
+
+Day14.run()