I don't think that it's one of the best solutions: here filter is called two times, so it's likely that you iterate two time on input, which is unnecessay. This can be solve with a vanilla for loop & one if.

Great solution 👏👏

Cool to define a enum for the membership categories.
I would put a contructor in the impl for this (i32, i32) as input.
Small note: I'm prertty sure the to string method is already implemented for structs.

Plz explain

Why does q have a size of 128? Couldn't it be size n?