Day 6: Probably a Fire Hazard

Section

defmodule P1 do
  def create_grid() do
    Enum.map(0..999, fn _ ->
      Enum.map(0..999, fn _ ->
        false
      end)
    end)
  end

  def update_grid(grid, "turn on", {x1, y1}, {x2, y2}) do
    update_range(grid, {x1, y1}, {x2, y2}, fn _ -> true end)
  end

  def update_grid(grid, "turn off", {x1, y1}, {x2, y2}) do
    update_range(grid, {x1, y1}, {x2, y2}, fn _ -> false end)
  end

  def update_grid(grid, "toggle", {x1, y1}, {x2, y2}) do
    update_range(grid, {x1, y1}, {x2, y2}, fn state -> not state end)
  end

  def update_range(grid, {x1, y1}, {x2, y2}, func) do
    Enum.with_index(grid)
    |> Enum.map(fn {row, x} ->
      if x >= x1 and x <= x2 do
        Enum.with_index(row)
        |> Enum.map(fn {cell, y} ->
          if y >= y1 and y <= y2 do
            func.(cell)
          else
            cell
          end
        end)
      else
        row
      end
    end)
  end
end

{:ok, data} = File.read("/Users/eli/Desktop/input.txt")
grid = P1.create_grid()

data
|> String.split("\n", trim: true)
|> Enum.reduce(grid, fn line, grid ->
  [command, x1, y1, x2, y2] =
    Regex.run(~r/(turn on|turn off|toggle) (\d+),(\d+) through (\d+),(\d+)/, line,
      capture: :all_but_first
    )

  {x1, y1, x2, y2} =
    {String.to_integer(x1), String.to_integer(y1), String.to_integer(x2), String.to_integer(y2)}

  P1.update_grid(grid, command, {x1, y1}, {x2, y2})
end)
|> Enum.flat_map(&amp; &amp;1)
|> Enum.count(&amp;(&amp;1 == true))

569999

defmodule P2 do
  def create_grid() do
    Enum.map(0..999, fn _ ->
      Enum.map(0..999, fn _ ->
        0
      end)
    end)
  end

  def update_grid(grid, "turn on", {x1, y1}, {x2, y2}) do
    update_range(grid, {x1, y1}, {x2, y2}, fn state -> state + 1 end)
  end

  def update_grid(grid, "turn off", {x1, y1}, {x2, y2}) do
    update_range(grid, {x1, y1}, {x2, y2}, fn state -> max(state - 1, 0) end)
  end

  def update_grid(grid, "toggle", {x1, y1}, {x2, y2}) do
    update_range(grid, {x1, y1}, {x2, y2}, fn state -> state + 2 end)
  end

  def update_range(grid, {x1, y1}, {x2, y2}, func) do
    Enum.with_index(grid)
    |> Enum.map(fn {row, x} ->
      if x >= x1 and x <= x2 do
        Enum.with_index(row)
        |> Enum.map(fn {cell, y} ->
          if y >= y1 and y <= y2 do
            func.(cell)
          else
            cell
          end
        end)
      else
        row
      end
    end)
  end
end

{:ok, data} = File.read("/Users/eli/Desktop/input.txt")
grid = P2.create_grid()

data
|> String.split("\n", trim: true)
|> Enum.reduce(grid, fn line, grid ->
  [command, x1, y1, x2, y2] =
    Regex.run(~r/(turn on|turn off|toggle) (\d+),(\d+) through (\d+),(\d+)/, line,
      capture: :all_but_first
    )

  {x1, y1, x2, y2} =
    {String.to_integer(x1), String.to_integer(y1), String.to_integer(x2), String.to_integer(y2)}

  P2.update_grid(grid, command, {x1, y1}, {x2, y2})
end)
|> Enum.flat_map(&amp; &amp;1)
|> Enum.sum()

17836115