How to Find All Occurrences of an Element in a Multiset in C++?

In C++, a multiset is a container similar to a set but it allows multiple occurrences of its elements i.e. duplicate values. In this article, we will learn how to find all occurrences of a specific element in a multiset in C++.

Example:

Input: 
myMultiset = {1, 2, 2, 3, 3, 3, 4, 4, 4, 4};
target = 3

Output: 
The element 3 occurred at position: 3 4 5

Finding All Occurrences of an Element in a Multiset in C++

To find all occurrences of an element in a std::multiset in C++, we can use the std::set::equal_range() function that returns the pair that contains the iterator to the range of set elements containing our target elements. We can then use the std::distance() function to get the position of these elements.

C++ Program To Find All Occurrences of an Element in a Multiset

The below example demonstrates how we can find all occurrences of an element in a multiset in C++.

C++

// C++ Program to illustrate how to find all occurrences of
// an element in a multiset
#include <iostream>
#include <set>
using namespace std;

int main()
{

    // Initialize a multiset with multiple occurrences of
    // some elements
    multiset<int> myMultiset
        = { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

    // The element to find
    int target = 3;

    cout << "The element " << target
         << " occurred at indices: ";

    // getting iterator to the range that contains the
    // matching elements
    auto it = myMultiset.equal_range(3);

    for (auto i = it.first; i != it.second; i++) {
        cout << distance(myMultiset.begin(), i) << " ";
    }

    return 0;
}

Output

The element 3 occurred at indices: 3 4 5 

Time Complexity: O(K + logN), here N is the number of elements in the multiset and K is the number of occurences.
Auxilliary Space: O(1)