livenumber.rb

def live_number(birthday)
  reduce("#{birthday.year}#{birthday.month}#{birthday.day}")
end

def reduce(sum)
  add_sum = each_digits(sum).reduce(:+)
  add_sum >= 10 ? reduce(add_sum) : add_sum
end

def each_digits(num)
  num.to_s.split("").map{|c| c.to_i }
end

livenumber_spec.rb

describe "live_number" do
 
  before :each do
    @birthdays = [Time.new(2001,3,5),
                  Time.new(1978,5,26),
                  Time.new(1962,10,1)]
    @birth = {:day => Time.new(1981,6,11), :ans => 9 }
  end
 
  it "return number of live by birthday" do
    @birthdays.each do |day|
      live_number(day).should be_a_kind_of(Fixnum)
    end
  end
 
  it "return the correct number of live" do
    @birthdays.each do |day|
      live_number(day).should == 2
    end
  end
 
  it "return correct number with specific birthday" do
    live_number(@birth[:day]).should == @birth[:ans]
  end
end