test.rb

def printgrid(table)
  strings = table.map do |row|
    row.map { |cell| cell.to_s }
  end

  column_widths = []
  strings.each do |row|
    row.each_with_index do |cell,i|
      column_widths[i] = [column_widths[i] || 1, cell.length + 2].max
    end
  end

  row_separator = "+" + column_widths.map { |width| "-" * width }.join("+") + "+"

  puts row_separator
  strings.each do |row|
    justified_row = row.enum_for(:map).with_index do |cell,i|
      " " + cell.ljust(column_widths[i] - 1)
    end
    puts "|" + justified_row.join("|") + "|"
    puts row_separator
  end
end

table = [[1,2,3],[4,5,6],[7,8,9],[100,200,300]]
printgrid(table)