def generate_empty_board
      board = []
      9.times do |_i|
        line = []
        9.times do |_j|
          line << {}
        end
        board << line
      end
      board
    end
def generate_empty_board
      board = []
      9.times do |_i|
        line = []
        9.times do |_j|
          line << {}
        end
        board << line
      end
      board
    end
return empty board jkf