Problem: Given an array answer queries(online) of the form [L,R]=number of distinct elements in the array from index L to R.

What different approaches/solutions are there to this problem.

Few approaches I know/heard of:

1.Using Segment/Merge-Sort tree (link:https://stackoverflow.com/questions/39787455/is-it-possible-to-query-number-of-distinct-integers-in-a-range-in-olg-n)

2.Modified Sqrt Decomposition (link:https://codeforces.net/blog/entry/44711?#comment-292719)

Are there any other interesting ways.

Also, what if we have update queries as well. (The above approaches will also work for updates but are there any other ways)