Knowing the exact number often requires extensive iteration because, for instance, hashed representations might have a significant number of elements marked MISSING due to assignments.
Getting an upper bound on the number isn't usually too hard, but it is still O(n) rather than O(1). On Fri, Oct 22, 2010 at 1:31 PM, Alexander Hans <[email protected]> wrote: > > It can be hard for an implementation to know the exact number of > > non-default elements. > > I can't quite see that. Can you elaborate please?
