defp largest_global_power(matrix) do
  max = {{nil, nil, nil}, nil}

  Enum.reduce(1..@grid_size, max, fn x, max ->
    Enum.reduce(1..@grid_size, max, fn y, max ->
      max_size = Enum.min([@grid_size - x, @grid_size - y])

      Enum.reduce(0..max_size, max, fn s, max ->
        square = Matrex.submatrix(matrix, x..(x + s), y..(y + s))
        tp = Matrex.sum(square)
        {_, max_tp} = max

        if is_nil(max_tp) or tp > max_tp do
          {{x, y, s}, tp}
        else
          max
        end
      end)
    end)
  end)
end