pascal_triangle.rb

class PascalTriangle

  attr_accessor :height

  def initialize(height)
    @height = height.to_i
  end

  def self.next_row(current_row)
    ([0] + current_row).zip(current_row + [0]).map{ |a| a.inject(:+) }
  end

  def draw
    current_row = [1] # always start at the top
    height.times do |i|
      puts current_row.join(' ')
      current_row = self.class.next_row(current_row)
    end
  end

  def self.tests_passing?
    [
      self.next_row([1]) == [1,1],
      self.next_row([1,1]) == [1,2,1],
      self.next_row([1,2,1]) == [1,3,3,1]
    ].all?
  end

end

raise 'BadTriangle' unless PascalTriangle.tests_passing?

PascalTriangle.new(ARGV[0]).draw