i am looking to solve the problemORDERSET. I was thinking about using Binary Index Tree but i dont think we'll be able to create such a large array(x<=10^9). Also i suppose the problem can be solved with a self balancing BST but the standard Java implementations dont provide efficient rank functionality. (it is O(n) in TreeSet) So are there some alternate ways to solve this problem besides implementing my own self balancing BST?