mutliplication_table.rb

def multiplication_table(n)
  str = "    |" + (" %3d" * n) % [*1..n]
  str += "\n"
  str += "----+" + "----" * n
  str += "\n"
  1.upto(n) do |x|
    str += "%3d |" % x
    1.upto(x-1) {|y| str += "    "}
    x.upto(n)   {|y| str += " %3d" % (x*y)}
    str += "\n"
  end
  str
end
 
multiplication_table 12