dryden, I agree that there is more than one solution if that is allowed, and it might have been made clearer. I am equally sure that the intended unique solution exits cells through the middle of each side. (In other words, all changes of direction are 90 degrees). The specially treated cell you refer to therefore indicates two sides, rather than one corner. And actually, taking the special cells as a group, this is a much more logical and consistent approach, which may be why it was not spelt out.