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

Set.retainAll() is how you find the intersection of two sets. If you use HashSet, then converting your ArrayLists to Sets and using retainAll() in a loop over all of them is actually O(n).