Efficient way to get middle (median) of an std::set?

Question

std::set is a sorted tree. It provides begin and end methods so I can get minimum and maximum and lower_bound and u

Answer 1

It's going to be O(size) to get the middle of a binary search tree. You can get it with std::advance() as follows:

std::set::iterator it = s.begin();
std::advance(it, s.size() / 2);