前面几个小节介绍了序列式容器，接下来介绍第一个关联式容器集合set。集合set类似数学上面的集合概念但有所区别就是multiset多值集合允许集合里面有重复的元素且是有序的。
基本方法：

//单个集合操作
insert();		//插入某个元素
count();		//统计集合里面元素个数
find();			//查找某个元素
......
------------------------------------------
//多个集合操作
set_union();				//并集
set_intersection();			//交集
set_difference();			//差集
set_symmetric_difference();	//对称差集

接着重点介绍下集合的交、并、差和对称差集，以多值集合S1和S2为例。
S1 = {1,3,5,7,9,11};S2 = {1,1,2,3,5,8,13};

结果示意图：

可运行代码：

//
// Created by wsk on 25-10-24.
//
#include <iostream>
#include <iterator>
#include <set>
using namespace std;

int main()
{
    int a1[6] = {1,3,5,7,9,11};
    int a2[7] = {1,1,2,3,5,8,13};
    multiset<int> s1(a1,a1+6);
    multiset<int> s2(a2,a2+7);
    auto it1 = s1.begin();
    cout << "s1: ";
    while (it1 != s1.end())
    {
        cout << *it1 << " " ;
        ++it1;
    }
    cout << endl;
    auto it2 = s2.begin();
    cout << "s2: ";
    while (it2 != s2.end())
    {
        cout << *it2 << " " ;
        ++it2;
    }
    cout << endl;
    auto first1 = s1.begin();
    auto last1 = s1.end();
    auto first2 = s2.begin();
    auto last2 = s2.end();
    // 1.并集
    cout << "s1 ∪ S2: ";
    set_union(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
    cout << endl;
    // 2.交集
    cout << "s1 ∩ S2: ";
    set_intersection(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
    cout << endl;
    // 3.差集
    cout << "s1 - S2: ";
    set_difference(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
    cout << endl;
    cout << "s2 - S1: ";
    set_difference(first2, last2, first1, last1, ostream_iterator<int>(cout, " "));
    cout << endl;
    // 4.对称差集s1 ⊕ S2 = (s1 - S2) ∪ (s2 - S1)
    cout << "s1 ⊕ S2: ";
    set_symmetric_difference(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
    cout << endl;
		return 0;
}