Roaring bitmaps are very interesting implementation. It's a mix of using arrays or bitsets (equivalent would be [1]) depending upon which are more efficient. I'

Roaring bitmaps are very interesting implementation. It's a mix of using arrays or bitsets (equivalent would be [1]) depending upon which are more efficient. I've used them in the past, and these are very effective, both for storage and for unions and intersections. [1]: https://en.cppreference.com/w/cpp/utility/bitset https://en.cppreference.com/w/cpp/utility/bitset