#!/usr/bin/ruby
func sierpinski_triangle(n) -> Array {
  var triangle = ['*']
  { |i|
    var sp = (' ' * pow(2, i));
    triangle = (triangle.map {|x| sp + x + sp} +
                triangle.map {|x| x + ' ' + x})
  } * n
  triangle
}
class Array {
    method display_2d {
        say self.join("\n")
    }
}
sierpinski_triangle(3).display_2d