What is the complexity of set_intersection in C++?

Question

What is the complexity of the following code?

set<int> S1, S2, ans;
set_intersection(S1.begin(), S1.end(), S2.begin(), S2.end(), inserter(ans, ans.begin()))

where S1 and S2 are some non_empty sets and ans is an empty set.

I know that inserting a sorted range into a set is linear; but is inserting using inserter linear too?

Answer 1

The inserter remembers where it last inserted each item and tries to insert the next item at the same place. This is O(1) if it's the right place.

Which means copying a sorted range to the inserter is linear overall, so you're good here.