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By C21, history, 5 weeks ago, In English,

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.com/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)

 
 
 
 
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Auto comment: topic has been updated by C21 (previous revision, new revision, compare).

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    5 weeks ago, # ^ |
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    But this is an offline approach.

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You can use a persistent segment tree in a very similar fashion to your first link.

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This is a Online Approach to the problem in O((N+Q)*logN) using persistent segment tree.

However, this doesn't work with updates as far as i know.