集合的运算（交集， 并集， 差集， 对称差）

交集

// set_intersection example
#include      // cout
#include     // set_intersection, sort
#include        // vector
using namespace std;
int main () {
    int first[] = {5,10,15,20,25};
    int second[] = {50,40,30,20,10};
    vector<int> v(10);                      // 0  0  0  0  0  0  0  0  0  0
    vector<int>::iterator it;

    sort (first,first+5);     //  5 10 15 20 25
    sort (second,second+5);   // 10 20 30 40 50

    it=set_intersection (first, first+5, second, second+5, v.begin());
                                               // 10 20 0  0  0  0  0  0  0  0
    v.resize(it-v.begin());                      // 10 20

    cout << "The intersection has " << (v.size()) << " elements:\n";
    for (it=v.begin(); it!=v.end(); ++it)
        cout << ' ' << *it;
        cout << '\n';

  return 0;
}/*The intersection has 2 elements:
 10 20
*/

并集

// set_union example
#include      // cout
#include     // set_union, sort
#include        // vector
using namespace std;
int main () {
    int first[] = {5,10,15,20,25};
    int second[] = {50,40,30,20,10};
    vector<int> v(10);                      // 0  0  0  0  0  0  0  0  0  0
    vector<int>::iterator it;

    //要用交集函数必须先排序
    sort (first,first+5);     //  5 10 15 20 25
    sort (second,second+5);   // 10 20 30 40 50

    it=set_union (first, first+5, second, second+5, v.begin());
                                               // 5 10 15 20 25 30 40 50  0  0
    v.resize(it-v.begin());                      // 5 10 15 20 25 30 40 50

    cout << "The union has " << (v.size()) << " elements:\n";
    for (it=v.begin(); it!=v.end(); ++it)
        cout << ' ' << *it;
        cout << '\n';

  return 0;
}
/*The union has 8 elements:
 5 10 15 20 25 30 40 50
*/

差集

// set_difference example
#include      // cout
#include     // set_difference, sort
#include        // vector
using namespace std;
int main () {
    int first[] = {5,10,15,20,25};
    int second[] = {50,40,30,20,10};
    vector<int> v(10);                      // 0  0  0  0  0  0  0  0  0  0
    vector<int>::iterator it;

    sort (first,first+5);     //  5 10 15 20 25
    sort (second,second+5);   // 10 20 30 40 50

    it=set_difference (first, first+5, second, second+5, v.begin());
                                               //  5 15 25  0  0  0  0  0  0  0
    v.resize(it-v.begin());                      //  5 15 25

    cout << "The difference has " << (v.size()) << " elements:\n";
    for (it=v.begin(); it!=v.end(); ++it)
        cout << ' ' << *it;
        cout << '\n';

    return 0;
}
/*The difference has 3 elements:
 5 15 25
*/

对称差

// set_symmetric_difference example
#include      // cout
#include     // set_symmetric_difference, std::sort
#include        // vector
using namespace std;
int main () {
    int first[] = {5,10,15,20,25};
    int second[] = {50,40,30,20,10};
    vector<int> v(10);                      // 0  0  0  0  0  0  0  0  0  0
    vector<int>::iterator it;

    sort (first,first+5);     //  5 10 15 20 25
    sort (second,second+5);   // 10 20 30 40 50

    it=set_symmetric_difference (first, first+5, second, second+5, v.begin());
                                               //  5 15 25 30 40 50  0  0  0  0
    v.resize(it-v.begin());                      //  5 15 25 30 40 50

    cout << "The symmetric difference has " << (v.size()) << " elements:\n";
    for (it=v.begin(); it!=v.end(); ++it)
        cout << ' ' << *it;
        cout << '\n';

  return 0;
 
}
/*The symmetric difference has 6 elements:
 5 15 25 30 40 50*/