元素数量严格小于给定数量

Question

I want a data structure in which I want to insert elements in log(n) time and the elements should be sorted in the ds after every insertion. I can use a multiset for this.

After that I want to find the numbers of elements strictly smaller than a given number again in log(n) time. And yes duplicates are also present and they need to be considered. For example if the query element is 5 and the ds contains {2, 2, 4, 5, 6, 8, 8} then answer would be 3(2, 2, 4) as these 3 elements are stricly lesser than 5

I could have used multiset but even if I use upper_bound I will have to use distance method which runs in linear time. How can I achieve this efficiently with c++ stl. Also I cannot use

Answer 1

The data structure you need is an order statistic tree: https://en.wikipedia.org/wiki/Order_statistic_tree

The STL doesn't have one, and they're not very common so you might have to roll your own. You can find code in Google, but I can't vouch for any specific implementation.