STL常用算法之set相关算法汇总2018.8.17

@set_union：set_union(first1, last1, first2, last2, result);

@set_intersection：set_intersection(first1, last1, first2, last2, result);

@set_difference：set_difference(first1, last1, first2, last2, result);

@set_symmetric_difference：set_symmetric_difference(first1, last1, first2, last2, result);