Efficiently finding the intersection of a variable number of sets of strings

Question

I have a variable number of ArrayList\'s that I need to find the intersection of. A realistic cap on the number of sets of strings is probably around 35 but could be more. I

Answer 1

You can use single HashSet. It's add() method returns false when the object is alredy in set. adding objects from the lists and marking counts of false return values will give you union in the set + data for histogram (and the objects that have count+1 equal to list count are your intersection). If you throw the counts to TreeSet, you can detect empty intersection early.