Set_intersection

    ...
    std::vector<int> v = {1, 2, 3, 4, 5};
    std::vector<int> w = {2, 4, 6, 8, 10};
    std::vector<int> x(v.size() + w.size());

    auto s = hpx::set_intersection(hpx::execution::par, v.begin(), v.end(), w.begin(), w.end(), x.begin());

    std::cout << "Common elements amount: " << std::distance(x.begin(), s) << std::endl;
    ...