怎样求交集,该如何解决

怎样求交集
vector <int>   group1;                   //   group1的内容是{   1,   2,   3,   4,   5,...}
vector <int>   group2;                   //   group2的内容是{   2,   3,   4,   6,   34,   22,...}
　　　　　　　　　　　　　　//   group内容是什么不重要
问题：怎样求   group1和group2   的交集呢？

------解决方案--------------------
要是排序好的话
algorithm中有个现成的算法 set_ 忘了具体的名字，好像就4个set_开头的算法
------解决方案--------------------
set_intersection
Syntax:

#include <algorithm>
iterator set_intersection( iterator start1, iterator end1, iterator start2, iterator end2, iterator result );
iterator set_intersection( iterator start1, iterator end1, iterator start2, iterator end2, iterator result, StrictWeakOrdering cmp );

The set_intersection() algorithm computes the intersection of the two sets defined by [start1,end1) and [start2,end2) and stores the intersection starting at result.

Both of the sets, given as ranges, must be sorted in ascending order.

The return value of set_intersection() is an iterator to the end of the intersection range.

If the strict weak ordering comparison function object cmp is not specified, set_intersection() will use the < operator to compare elements.