staqueue.rb

require './stack'

class Staqueue
  def initialize
    @s1 = Stack.new
    @s2 = Stack.new
  end

  def empty?
    @s1.empty?
  end

  def enqueue(item)
    while [email protected]?
      @s2.push(@s1.pop)
    end
    @s1.push(item)
    while [email protected]?
      @s1.push(@s2.pop)
    end
  end

  def dequeue
    @s1.pop()
  end

  def size
    @s1.size
  end
end

staqueue_spec.rb

require './staqueue'

describe Staqueue do
  subject do
    Staqueue.new
  end

  it "initializes as empty queue" do
    subject.should be_empty
  end

  describe "#enqueue" do
    it "adds an item to queue" do
      subject.enqueue(double)
      subject.should_not be_empty
    end
  end

  describe "#dequeue" do
    it "returns nil if empty" do
      subject.dequeue.should be_nil
    end
    it "removes an item from queue" do
      subject.enqueue(double)
      subject.dequeue
      subject.should be_empty
    end
    it "removes and returns the oldest item from queue" do
      subject.enqueue(:item1)
      subject.enqueue(:item2)
      subject.enqueue(:item3)
      subject.dequeue.should == :item1
      subject.dequeue.should == :item2
      subject.dequeue.should == :item3
    end
  end

  describe "#size" do
    it "returns the number of items added to queue" do
      16.times { subject.enqueue(double) }
      subject.size.should == 16
      3.times { subject.dequeue }
      subject.size.should == 13
    end
  end
end