i dont even know what filtering function is

Agreed: filter lies in the paradigm of functional programming, and the proposed answers relies on count to keep some permanent state (in fact, modifying c counter, while filter does the looping).

So, while I find it clever, this solution is not easy to understand.

IMO this solution, while it works and short, is not a good practice:
the filtering function has its side effect (actually, that's the reason it works).
I think that filtering functions should not have side effects, so that we can move them around the code and reused them elsewhere.