STL源码剖析之算法：set_union & set_intersection

template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_union(InputIterator1 first1, InputIterator1 last1,
                         InputIterator2 first2, InputIterator2 last2,
                         OutputIterator result) {
    while(first1 != last1 && first2 != last2) {
        if(*first1 < *first2) {
            *result = *first1;
            ++first1;
        } else if(*first2 < *first1) {
            *result = *first2;
            ++first2;
        } else {
            *result = *first1;
            ++first1;
            ++first2;
        }
        ++result;
    }

    return copy(first1, last1, copy(first2, last2, result));
}

 

template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_intersection(InputIterator1 first1, InputIterator1 last1,
                                InputIterator2 first2, InputIterator2 last2,
                                OutputIterator result) {
    while(first1 != last1 && first2 != last2) {
        if(*first1 < *first2)
            ++first1;
        else if(*first2 < *first1)
            ++first2;
        else {
            *result = *first1;
            ++first1;
            ++first2;
            ++result;
        }
    }

    return result;
}