tecnically you dont have to use any resistors. but I would not recomend it. resistors protect the led's from getting too much current, if they get too much they will burn out quickly.
to calculate what resistors you need, you need four variables.
1=FV of the LED
2=current of led
3= supply voltage
4= number of leds
I can answer numbers one and two for you the others you are on your own, or maybe someone here knows supply voltage for a DS as I have never touched one.
answer:
1=3.0V
2=20ma
use this calculator when you have the other two variables and it will tell you what resistor to use.
http://www.led-calculator.com/