Question

I have an array which is not necessarily full.

It can be very sparse.

Is there a good way to iterate through this array without visiting all the possible indexes? (c++ array iterator?)

Or, even if I use array iterator, will it be nothing different from visiting every indexes and checking the value?

Answer 1

Yes, if you use an iterator, it’s the same as visiting every index and checking the value, and there’s no good way to skip logical holes. You could keep a list of good indices, but if you did that then why not just use a list to store the data in the first place?

If your data is very sparse, perhaps a better data structure would be a std::map, or even an std::unordered_map, depending on your application. These have decent lookup time while not wasting much space, like an array would have to.