If I told you to count how many different users have visited a high traffic website, how would you do it? It’s not trivial, is it? Probably, the first idea that would come to every programmer’s mind would be to use some kind of set with the user id in it. That’s not bad at all: each access to the hash set is constant. However, having to keep each element in memory doesn’t seem very optimal, we’d be wasting a lot of memory… What if we were counting something with a very high cardin...
