Day - 11

Setup

Mix.install([
  {:kino, "~> 0.4.1"}
])

input = Kino.Input.textarea("Please enter your Input")

defmodule Recursion do
  def step(grid) do
    flash(Map.keys(grid), grid, MapSet.new())
  end

  defp flash([{row, col} = key | keys], grid, flashed) do
    value = grid[key]

    cond do
      is_nil(value) or key in flashed ->
        flash(keys, grid, flashed)

      grid[key] >= 9 ->
        keys = [
          {row - 1, col - 1},
          {row - 1, col},
          {row - 1, col + 1},
          {row, col - 1},
          {row, col + 1},
          {row + 1, col - 1},
          {row + 1, col},
          {row + 1, col + 1}
          | keys
        ]

        flash(keys, Map.put(grid, key, 0), MapSet.put(flashed, key))

      true ->
        flash(keys, Map.put(grid, key, value + 1), flashed)
    end
  end

  defp flash([], grid, flashed) do
    {grid, MapSet.size(flashed)}
  end

  def inspect({grid, flashes}) do
    for row <- 0..9 do
      IO.puts(for col <- 0..9, do: grid[{row, col}] + ?0)
    end

    IO.puts("flashes: #{flashes}")
    grid
  end
end

lines =
  input
  |> Kino.Input.read()
  |> String.split("\n", trim: true)

grid =
  for {line, row} <- Enum.with_index(lines),
      {energy, col} <- Enum.with_index(String.to_charlist(line)),
      into: %{},
      do: {{row, col}, energy - ?0}

:ok

Part 1

1..100
|> Enum.map_reduce(grid, fn _, grid ->
  {grid, flashes} = Recursion.step(grid)
  {flashes, grid}
end)
|> elem(0)
|> Enum.sum()

Part 2

Stream.iterate(1, &(&1 + 1))
|> Enum.reduce_while(grid, fn i, grid ->
  case Recursion.step(grid) do
    {grid, flashes} when map_size(grid) == flashes -> {:halt, i}
    {grid, _flashes} -> {:cont, grid}
  end
end)