Hello everyone, I hope you are doing well, can anybody explain to me why this code costs O(n) on sets and multiset but in the other side it costs O(log(n)) on the sorted vectors.

the code ->

multiset ms; int x ; auto it = upper_bound(ms.begin() , ms.end() , x) ;

between this code cost O(log(n)) auto it = ms.upper_bound(x);