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

In C++, vectors are containers that store the elements in contiguous memory locations just like arrays. The frequency of a specific element means how many times that particular element occurs in a vector. In this article, we will learn how to find the frequency of a specific element in a vector in C++.

Example

Input:
myVector = {10,20,50,10,20,40,30,10,20,10}
Target =10

Output:
The frequency of 10 is: 4

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

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

Syntax of std::count()

count(first, last, val)

Here,

• first, last: Input iterators to the initial and final positions of the sequence of elements. 
• val: Value to match

C++ Program to Find the Frequency of an Element in a Vector

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

C++

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

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

int main()
{
    // Initializing a vector
    vector<int> vec
        = { 10, 20, 50, 10, 20, 40, 30, 10, 20, 10 };
    int target = 10;
    // Finding the frequency of target element using count
    int frequency = count(vec.begin(), vec.end(), target);

    // Print the Vector Elements
    cout << "Vector Elements: ";
    for (auto ele : vec) {
        cout << ele << " ";
    }
    cout << endl;

    // Print the frequency of the target element
    cout << "The Frequency of " << target
         << " is: " << frequency << endl;
    return 0;
}

Output

Vector Elements: 10 20 50 10 20 40 30 10 20 10 
The Frequency of 10 is: 4

Time Complexity: O(N), here N is the size of the vector.
Auxiliary Space: O(1)