How to Find Frequency of an Element in a List in C++?

In C++, lists are sequence containers that allow non-contiguous memory allocation. They are implemented as doubly-linked lists. The frequency of a specific element means how many times that particular element occurs in a list. In this article, we will learn how to find the frequency of a specific element in a list in C++ STL.

Example:

Input: 
myList = {10, 31, 20, 31, 31, 40};
Target = 31

Output:
Frequency of 31 is : 3

Find the Frequency of an Element in a List in C++

To find the frequency of a specific element in a std::list in C++, we can use the std::count() method that counts the occurrences of a given target value within a specified range in a list.

Syntax to Find Frequency of an Element in C++

count(listName.begin(), listName.end(), target);

Here,

• begin() and end() are input iterators to the initial and final positions of the sequence of elements.
• target is the element whose frequency is required.

C++ Program to Find the Frequency of a Specific Element in a List

The below example demonstrates how we can use the std::count() function to find the frequency of a specific element in a list in C++ STL.

C++

// C++ program to illustrate how to find the frequency of a
// specific element in a list

#include <algorithm>
#include <iostream>
#include <list>
using namespace std;

int main()
{
    // Initializing a list of integers
    list<int> myList = { 10, 31, 20, 31, 31, 40 };

    // Declare element whose frequency is required
    int target = 31;

    // Finding the frequency of the target element
    int frequency
        = count(myList.begin(), myList.end(), target);

    // Printing the frequency of the element
    cout << "Frequency of " << target
         << " is : " << frequency << endl;

    return 0;
}

Output

Frequency of 31 is : 3

Time Complexity: O(N), where N is the number of elements in the list.
Auxiliary Space: O(1)