The trick is in the dist() function, which compute how far two circles are.

Note: this code would gain a lot to be rewritten to use a class with named fields, instead of using an array of anonymous values.

I understand that its finding the distance, but I don't quite grasp how the new arrays are being filled. Are they being ordered by distance and the dist() automatically fills the e[k][] arrays.

" how the new arrays are being filled"
There are no new arrays?

" the dist() automatically fills the e[k][] arrays"
Uh? dist() is only used in a conditional, its value doesn't go to an array. No ordering either, only brute force, comparing everything twice (x vs. y then y vs. x, and even x vs. x).

Arrays are still necessary, but an array of objects. The idea is to make a class defining fields like x, y, radius, xSpeed, ySpeed, and create a new instance for each circle with the random values. Thus, you would access circle[j].x instead of circle[j][0], which is more expressive and less prone to errors.

thanks i'll give it a shot.