Sets in C++

Sets Represent Mathematical Sets, I have plently of notes on Sets in my Discrete Mathematical Section!!

templated for one type (e.g. set of int, set of strings, set of long)
They hold only one example of any element, if you add a duplicate of an existing element, it is ignored

Insert and Erase are Similar to Map’s

Insert on a set retruns a pair
- while the iterator points to the base type (int, double, string), not the pair
When you erase, it erases all examples of the key (which is only one)
Iterator on sets are constant, you can’t change a key in place

Inserting into a set example

#include<iostream>
using std::cout; using std::endl;
#include<iterator>
using std::ostream_iterator;
#include<set>
using std::set;
#include<string>
using std::string;

int main()
{
    set<string> NBA;

    // insert method

    NBA.insert("Jordan");
    NBA.insert("Lebron");
    NBA.insert("Kobe");

    //declaring iterator to a set
    set<string>::iterator it;

    cout << "Elements of the set:     ";

    for (it = NBA.begin(); it != NBA.end(); it++)
    {
        cout << *it << ", ";
    }
    cout << endl;
}

Output

Elements of the set:     Jordan, Kobe, Lebron, 

Removing an Element from a set Example

NBA.erase("Jordan");

cout << "After removing the GOAT:   ";

for (it = NBA.begin(); it != NBA.end(); it++)
{
    cout << *it << ", ";
}
cout << endl;

Output

After removing the GOAT:   Kobe, Lebron,

Remember when we learned about sets in Discrete Mathmatics and about Union, intersection, etc?

We can perform these on sets using generic Algorithms but for the Algorithms to work on the container, the container MUST BE sorted.

Set Algorithms

set_union
set_intersection
set_difference
set_symmetric_difference

Set Algorithm Examples

inserting an Image

other things to do with Sets

#include<iostream>
using std::cout; using std::endl;
#include<set>
using std::set;
#include<vector>
using std::vector;
#include<iterator>
using std::ostream_iterator;
#include<algorithm>
using std::set_union; using std::set_intersection;
using std::set_difference;
using std::set_symmetric_difference;
using std::sort; using std::find;

int main (){

    // Regular sets get sorted automatically in C++
    set<long> set1 = {5,3,1,4,2};
    set<long> set2 = {1,8,3,5,9};

    //print our set
    cout << "Set 1: ";
    for (auto element : set1 )
    {
        cout << element << ", ";
    }
    cout << endl;

    cout << "Set 2: ";
    for (auto element : set2)
    {
        cout << element << ", ";
    }
    cout << endl;

}

Output

Set 1: 1, 2, 3, 4, 5, 
Set 2: 1, 3, 5, 8, 9,

Using the .find() algorithm on a Set

#include<iostream>
using std::cout; using std::endl;
#include<set>
using std::set;
#include<algorithm>
using std::find;

int main (){

    // Regular sets get sorted automatically in C++
    set<long> set1 = {5,3,1,4,2,6};   
    set<long> set2 = {1,8,3,5,9};

    set<long>::iterator iter, st;

    long search_for = 4;

    // iterator points to a position where 4 is
    iter = find(set1.begin(), set1.end(), search_for);

    cout << "The elements in the Set that come after " << search_for << " are: ";
    for (  st = iter; st != set1.end(); st++)
    {
        cout << *st << " ";
    }
    cout << endl;

}

Output

The elements in the Set that come after 4 are: 4 5 6 

Can also use the method of find() in sort by using this

iter = set1.find(search_for);

Set Union, Set intersection, and Symmetric Difference

#include<iostream>
using std::cout; using std::endl;
#include<set>
using std::set;
#include<algorithm>
using std::find;
using std::set_union; using std::set_intersection;
using std::set_difference;
using std::set_symmetric_difference;
using std::sort;
#include<vector>
using std::vector;
#include<iterator>
using std::ostream_iterator;


int main (){

    ostream_iterator<long> os_itr (cout, ", ");

    // Regular sets get sorted automatically in C++
    set<long> set1 = {5,3,1,4,2,6};   
    set<long> set2 = {1,8,3,5,9};

    cout << "Union: " << endl;

    set_union(set1.begin(), set1.end(), set2.begin(), set2.end(), os_itr);

    cout << '\n';

    cout << "Intersection: " << endl;

    set_intersection(set1.begin(), set1.end(), set2.begin(), set2.end(), os_itr);

    cout <<'\n';

    cout << "Symmetric Difference: " << endl;
    
    set_symmetric_difference(set1.begin(), set1.end(), set2.begin(), set2.end(), os_itr);

    cout << endl;

}

Output

Union: 
1, 2, 3, 4, 5, 6, 8, 9, 
Intersection: 
1, 3, 5, 
Symmetric Difference: 
2, 4, 6, 8, 9, 