Representing sparse integer sets?

Question

What is a good way to represent sparse set of integers (really C memory addresses) in a compact and fast way. I already know about the obvious things like bit-vectors and ru

Answer 1

A very compact data structure would be a bloom filter, perhaps a counting bloom filter to support deletions.

http://en.wikipedia.org/wiki/Bloom_filter

The Bloom filter, conceived by Burton H. Bloom in 1970, is a space-efficient probabilistic data structure that is used to test whether an element is a member of a set. False positives are possible, but false negatives are not. Elements can be added to the set, but not removed (though this can be addressed with a counting filter)