C++ Using STL Unordered Multiset Program

Hello Everyone!

In this tutorial, we will learn about the working of Multiset in STL and its implementation in the C++ programming language.

What is a Multiset?

Multisets are similar to set, with the exception that multiple elements can have the same values (duplicates are retained).

What is an Unordered Multiset?

It is the same as a Multiset but here the elements are not sorted but are stored in random order.

For a better understanding of its implementation, refer to the well-commented C++ code given below.

Code:

#include <iostream>
#include <bits/stdc++.h>

using namespace std;

//Function to print the elements of the vector using an iterator
void showVector(vector<int> v)
{
    //declaring an iterator to iterate through the vector elements
    vector<int>::iterator i;

    for (i = v.begin(); i != v.end(); i++)
    {
        cout << *i << "  "; //accessing the elements of the vector using * as i stores the address to each element
    }

    cout << endl;
}

//Function to print the elements of the unordered multiset using an iterator
void showMultiset(unordered_multiset<int> s)
{
    //declaring an iterator to iterate through the multiset
    unordered_multiset<int>::iterator i;

    for (i = s.begin(); i != s.end(); i++)
    {
        cout << *i << "  "; //accessing the elements of the unordered multiset using * as i stores the address to each element
    }

    cout << endl;
}

int main()
{
    cout << "\n\nWelcome to Studytonight :-)\n\n\n";
    cout << " =====  Program to demonstrate the working of a Unordered Multiset, in CPP  ===== \n\n\n\n";

    cout << "*** Multisets are similar to set, with an exception that multiple elements can have same values. *** \n\n";

    cout << "*** Unordered Multisets stores its elements in a random order depending on the hash method used internally. *** \n\n";

    //Unordered Multiset declaration (Set of integers where duplicates are allowed)
    unordered_multiset<int> s;

    //Filling the elements by using the insert() method.
    cout << "\n\nFilling the Multiset with integers in random order."; //Unordered Multiset stores them in a random order

    s.insert(50);
    s.insert(30);
    s.insert(50);
    s.insert(80);
    s.insert(30);
    s.insert(60);

    cout << "\n\nThe number of elements in the Unordered Multiset are: " << s.size();

    cout << "\n\nThe elements of the Unordered Multiset are: ";
    showMultiset(s);

    //Sorting the unordered multiset by copying its elements to a vector
    vector<int> v(s.begin(), s.end());

    vector<int>::iterator it;

    cout << "\n\nThe elements of the Unordered Multiset after sorting using a vector are: ";

    //sorting the vector elements in ascending order
    sort(v.begin(), v.end());

    showVector(v);

    cout << "\n\n\n";

    return 0;
}

Output:

We hope that this post helped you develop a better understanding of the concept of an Unordered Multiset in STL and its implementation in C++. For any query, feel free to reach out to us via the comments section down below.

Keep Learning : )