C ++ STL seek union, intersection, difference

Seeking union:std::set_union

The two sets and set into the vector.

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main()
{
    set<int> a;
    set<int> b;
    a.insert(1);
    a.insert(3);
    a.insert(5);
    a.insert(4);
    a.insert(9);
    a.insert(6);

    b.insert(5);
    b.insert(6);
    b.insert(7);

    vector<int> result;
    set_union(a.begin(),a.end(),b.begin(),b.end(),inserter(result,result.begin()));
    for(int i=0;i<result.size();i++)
    {
        cout<<result[i]<<" ";
    }
    return 0;
}

operation result

1 3 4 5 6 7 9

Note : set with ordered, that is to insert elements will automatically sort, but if you need to evaluate vector union, intersection, difference operation, please use the advance sort函数order.

Intersection of:set_intersection

Vector intersection of two, and the result is retained until the vector.
This time we inserted data has been ordered, and does not require sorting.

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main()
{
    vector<int> a;
    vector<int> b;
    a.push_back(1);
    a.push_back(3);
    a.push_back(5);
    a.push_back(6);
    a.push_back(7);
    a.push_back(10);

    b.push_back(5);
    b.push_back(6);
    b.push_back(7);

    vector<int> result;
    set_intersection(a.begin(),a.end(),b.begin(),b.end(),inserter(result,result.begin()));

    for(int i=0;i<result.size();i++)
    {
        cout<<result[i]<<" ";
    }
    return 0;
}

operation result:

5 6 7

Differencing set:set_difference

Differencing the two vector sets, placed in a new vector.

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int main()
{
    vector<int> a;
    vector<int> b;
    a.push_back(1);
    a.push_back(3);
    a.push_back(5);
    a.push_back(6);
    a.push_back(7);
    a.push_back(10);

    b.push_back(5);
    b.push_back(6);
    b.push_back(7);

    vector<int> result;
    set_difference(a.begin(),a.end(),b.begin(),b.end(),inserter(result,result.begin()));

    for(int i=0;i<result.size();i++)
    {
        cout<<result[i]<<" ";
    }
    return 0;
}

operation result:

1 3 10

Supplements

It should be noted that these three functions and will not help us to complete the 去重operation, if necessary 去重, use the uniquefunction.

Order intersection, for example, the presence of the same element in the vector.

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main()
{
    vector<int> a;
    vector<int> b;
    a.push_back(1);
    a.push_back(3);
    a.push_back(5);
    a.push_back(5);
    a.push_back(7);
    a.push_back(10);

    b.push_back(5);
    b.push_back(5);
    b.push_back(7);

    vector<int> result;
    set_intersection(a.begin(),a.end(),b.begin(),b.end(),inserter(result,result.begin()));

    for(int i=0;i<result.size();i++)
    {
        cout<<result[i]<<" ";
    }
    return 0;
}

operation result

5 5 7

If you do not want is equal, for example, by

result.erase(unique(result.begin(),result.end()), result.end());

To resolve.