unordered set intersection in C++

Question

Here is my code, wondering any ideas to make it faster? My implementation is brute force, which is for any elements in a, try to find if it also in b, if so, put in result s

Answer 1

You can do it with std::copy_if()

std::copy_if(a.begin(), a.end(), std::inserter(c, c.begin()), [b](const int element){return b.count(element) > 0;} );