C++ 求取交集个数

GetSetIntersectionNumber.cc

struct MeteringIterator: public std::iterator<std::output_iterator_tag, void, void, void, void> {
public:
    MeteringIterator(size_t *times_ptr) noexcept :
        times(times_ptr) {
        *times = 0;
    }

    template <typename T>
    MeteringIterator& operator= (T &&elem) noexcept {
        ++*times;
        return *this;
    }

    MeteringIterator& operator* () noexcept {
        return *this;
    }

    MeteringIterator& operator++ () noexcept {
        return *this;
    }

    MeteringIterator operator++ (int) noexcept {
        return *this;
    }

public:
    size_t *times = nullptr;
};

template< class InputIt1, class InputIt2>
inline size_t GetSetIntersectionNumber(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2) {
    size_t times = 0;
    std::set_intersection(first1, last1, first2, last2, MeteringIterator{&times});
    return times;
}