C program to find the most popular element in an array

In this blog post, we learn how to write a C program to find the most popular element in an array? So here we will write the program to find the most popular element in an array. We will also see how to display the most frequent element in an array using C programming.

Example,

Input : arr[] = {1, 3, 2, 1, 4, 1};

Output: 1

Explanation: 3 appears three times in the array which is the maximum frequency.

So let’s see the logic to find the most popular element in an array. Suppose arr is an integer array of size N (arr[N] ), the task is to write the C program to find the most popular element in an array.

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Solution 1: Brute Force

It is the simplest solution to find the most popular element in an array. In which you need to use nested loops. The outer loop picks elements one by one and the inner loop is scanning picks elements’ entire array to find their duplicates.

Here we are also maintaining two important variables ‘count’ and ‘popular’. The count variable store the maximum frequency and the popular store the element which has a maximum frequency.

#include<stdio.h>

//Calculate array size
#define ARRAY_SIZE(a)  sizeof(a)/sizeof(a[0])


int getMostPopularElement(int arr[], const int n)
{
    int count = 1, tempCount;
    int temp = 0,i = 0,j = 0;

    //Get first element
    int popular = arr[0];
    for (i = 0; i < (n- 1); i++)
    {
        temp = arr[i];
        tempCount = 0;
        for (j = 1; j < n; j++)
        {
            if (temp == arr[j])
                tempCount++;
        }
        if (tempCount > count)
        {
            popular = temp;
            count = tempCount;
        }
    }
    return popular;
}



int main()
{
    int arr[] = {1, 2, 3, 2, 3, 1, 3, 4, 4};

    const int N = ARRAY_SIZE(arr);

    const int popular = getMostPopularElement(arr, N);

    // print the most occurring numbers
    printf(" %d \n\n", popular);

    return 0;
}

Output:

Solution 2. Using Sorting

It is an optimized solution to find the maximum frequency of an element. In this solution first, we will sort the given array. Here I am sorting the array using the qsort library function. If you want you can create your own version of the array sorting function.

Now after sorting the array, all duplicate elements will get aligned. We can now linearly find the frequency of all elements in the array. The time complexity of this solution is O(n log n) and space complexity O(1).

#include<stdio.h>
#include <stdlib.h>

//Calculate array size
#define ARRAY_SIZE(a)  sizeof(a)/sizeof(a[0])


//call back function
int compare(const void * a, const void * b)
{
    return ( *(int*)a - *(int*)b );
}

//function to get most popular array element
int getMostPopularElement(int arr[], const int n)
{
    //sort array elements using qsort inbuilt function
    qsort( arr,n, sizeof(int), compare);

    // find the max popularity of element using linear traversal
    int count = 1, popular = arr[0], tempCount = 1, i= 0;
    for (i = 1; i < n; i++)
    {
        if (arr[i] == arr[i - 1])
        {
            tempCount++;
        }
        else
        {
            if (tempCount > count)
            {
                count = tempCount;
                popular = arr[i - 1];
            }
            tempCount = 1;
        }
    }
    // If last element is most frequent
    if (tempCount > count)
    {
        count = tempCount;
        popular = arr[n - 1];
    }

    return popular;
}




int main()
{
    int arr[] = {1, 2, 3, 2, 3, 1, 3, 4, 4};

    const int N = ARRAY_SIZE(arr);

    const int popular = getMostPopularElement(arr, N);

    // print the most occurring numbers
    printf(" %d \n\n", popular);

    return 0;
}