prime_factor_spec.rb

class PrimeFactor
  def initialize(number)
    @factors = Fiber.new do
      divisor = 2
      while divisor < number
        while number % divisor == 0
          Fiber.yield divisor
          number = number / divisor
        end
        divisor = divisor + 1
      end
      Fiber.yield number if number > 1
    end
  end

  def next
    @factors.resume
  end
end

describe PrimeFactor do
  it "factors 1" do
    factors = PrimeFactor.new(1)
    factors.next.should be_nil
  end

  it "factors 2" do
    factors = PrimeFactor.new(2)
    factors.next.should == 2
  end

  it "factors 3" do
    factors = PrimeFactor.new(3)
    factors.next.should == 3
  end

  it "factors 4" do
    factors = PrimeFactor.new(4)
    factors.next.should == 2
    factors.next.should == 2
  end

  it "factors 5" do
    factors = PrimeFactor.new(5)
    factors.next.should == 5
  end

  it "factors 6" do
    factors = PrimeFactor.new(6)
    factors.next.should == 2
    factors.next.should == 3
  end

  it "factors 7" do
    factors = PrimeFactor.new(7)
    factors.next.should == 7
  end

  it "factors 8" do
    factors = PrimeFactor.new(8)
    factors.next.should == 2
    factors.next.should == 2
    factors.next.should == 2
  end

  it "factors 9" do
    factors = PrimeFactor.new(9)
    factors.next.should == 3
    factors.next.should == 3
  end

  it "factors a large number" do
    factors = PrimeFactor.new(2*3*5*7*11*13*17)
    factors.next.should == 2
    factors.next.should == 3
    factors.next.should == 5
    factors.next.should == 7
    factors.next.should == 11
    factors.next.should == 13
    factors.next.should == 17
  end

  # it "factors 1" do
  #   PrimeFactor.of(1).should == []
  # end

  # it "factors 2" do
  #   PrimeFactor.of(2).should == [2]
  # end

  # it "factors 3" do
  #   PrimeFactor.of(3).should == [3]
  # end

  # it "factors 4" do
  #   PrimeFactor.of(4).should == [2, 2]
  # end

  # it "factors 5" do
  #   PrimeFactor.of(5).should == [5]
  # end

  # it "factors 6" do
  #   PrimeFactor.of(6).should == [2, 3]
  # end

  # it "factors 7" do
  #   PrimeFactor.of(7).should == [7]
  # end

  # it "factors 8" do
  #   PrimeFactor.of(8).should == [2, 2, 2]
  # end

  # it "factors 9" do
  #   PrimeFactor.of(9).should == [3, 3]
  # end
end