triangle.rb

class Triangle
  attr_reader :rows

  def initialize height
    factorial = [1]
    1.upto(height).each { |n| factorial << n * factorial.last }

    @rows = 0.upto(height - 1).map do |row|
      0.upto(row).map { |seq| factorial[row] / (factorial[seq] * factorial[row - seq]) }
    end
  end
end