your post should look like:

It is your responsibility to make your posts legible. To leave a post in the form of your origibnal post shows a lack of respect for potential helpers.Hi,

Let R be a set of n red points in the plane, and a let B be a set of n blue points in the plane.

We call a line L a separator for R and B if L has all points of R to one side and all points of B to the other side.

I need to find a randomized algorithm that can decide in O(n) expected time whether R and B have a separator.

Any idea please?

CB