Random position, but not overlapping

programming flash
1

Hi!
I read this (great) tutorial http://www.kirupa.com/developer/actionscript/connectedLines.htm
and I’m trying to generate more “blueCircles”.
Everything goes OK, but, sometimes, it’s overlapping.
How can I generate it not-so-random?
I mean: random, but without overlapping?

Thanks for helping.