By shanto_bangladesh, history, 6 months ago,

I tried to find the index of the upper_bound of an integer in a set.

set<int> s = {1,2,3,4,5};
int ind = s.upper_bound(2) - s.begin();
cout << ind << "\n";


But it's showing error. I did similar thing with vectors previously. Code looks like the following:

vector<int> v = {1,2,3,4,5};
int ind = upper_bound(v.begin(), v.end(), 2) - v.begin();
cout << ind << "\n;


The above code nicely executes the desired task. Why it's not working for set and multiset and what to do if we want to do the same task with a set or multiset without traversing the whole set?

 » 6 months ago, # |   +6 std::set (or multiset, doesn't matter) doesn't allow you to do it fast. To calculate the index you should think of easier solution for the problem that doesn't involve it; it's too difficult use some more advanced data structures, for example ordered_set (see here). But actually, pay attention to the striked text!