day04: part 2

lib/day04.ex

···
     |> Grid.get_reachable_ats()
     |> Enum.count()
   end
+
+  def solve_part_2(%Grid{} = grid) do
+    remove_till_no_reachable_ats(grid, 0)
+  end
+
+  def remove_till_no_reachable_ats(%Grid{} = grid, acc_count) do
+    case Grid.remove_and_count_reachable_ats(grid) do
+      {_, 0} -> acc_count
+      {new_grid, count} -> remove_till_no_reachable_ats(new_grid, acc_count + count)
+    end
+  end
 end

lib/day04/grid.ex

···
     %__MODULE__{grid_map: grid_map, width: width, height: height}
   end
 
+  def remove_and_count_reachable_ats(%__MODULE__{} = grid) do
+    grid
+    |> get_reachable_ats()
+    |> Enum.reduce({grid, 0}, fn coord, {grid, count} ->
+      {%{grid | grid_map: Map.put(grid.grid_map, coord, ".")}, count + 1}
+    end)
+  end
+
   def get_reachable_ats(%__MODULE__{grid_map: grid_map, width: width, height: height}) do
     for x <- 0..(width - 1),
         y <- 0..(height - 1),