Sort elements by frequency of occurrences code in C

March 23, 2023

Sort elements by frequency of occurrences

Here, in this page we will discuss the C program to sort array elements in such a way that the element with the highest number of occurrences comes first. If the number of occurrences are equal then the print the number which appeared first in the array.

Sort Elements by Frequency of Occurrences in C

To solve sort elements by frequency of occurrences in C we can use an array to count the occurrences of each element , and then use a sorting algorithm to sort the elements by their counts . Lets see this in detail .

Algorithm

Take the size of the array and store it in variable n.
Declare two array of n size and named them as arr[] and mp[].
Take the elements of the array from the user and store them in one array.
Calculate the frequency of each element of the array and store it in frequency array.
Then sort the frequency array. And print the elements according to their frequency count.

Overall, this algorithm has a time complexity of O(n^2), where n is the size of the input array, due to the use of an insertion sort algorithm. If a more efficient sorting algorithm is used, such as quicksort or mergesort, the time complexity can be improved to O(n log n). However, the basic idea of using an array to count the occurrences of each element and then sorting by the counts remains the same.

Size of sub-array with max sum

Sub-array with given sum

Triplet that sum to a given value

Segregate 0’s and 1’s in array

Segregate 0’s 1’s and 2’s in array

Code for Sort Elements by Frequency of Occurrences in C

Run

#include <stdio.h>

int main ()
{
  int k = 0, n, temp, count;

  printf ("Enter the number of elements:\n");
  scanf ("%d", &n);

  int arr[n][2], mp[n][2];

  printf ("\nEnter the array elements :\n");
  for (int i = 0; i < n; i++)
    {
      scanf ("%d", &arr[i][0]);
      arr[i][1] = 0;
    }

  for (int i = 0; i < n; i++)
    {

      if (arr[i][1])
	continue;

      count = 1;
      for (int j = i + 1; j < n; j++)
	{

	  if (arr[i][0] == arr[j][0])
	    {
	      arr[j][1] = 1;
	      count++;
	    }
	}

      mp[k][0] = arr[i][0];
      mp[k][1] = count;
      k++;


    }
  n = k;

  for (int i = 0; i < n - 1; i++)
    {

      temp = mp[i][1];
      for (int j = i + 1; j < n; j++)
	{

	  if (temp < mp[j][1])
	    {
	      temp = mp[j][1];
	      mp[j][1] = mp[i][1];
	      mp[i][1] = temp;

	      temp = mp[j][0];
	      mp[j][0] = mp[i][0];
	      mp[i][0] = temp;
	    }
	}

    }


  printf ("\n Sorted Array based on its frequency:\n");
  for (int i = 0; i < n; i++)
    {

      while (mp[i][1] != 0)
	{

	  printf (" %d  ", mp[i][0]);
	  mp[i][1]--;

	}

    }
  return 0;
}

Output

Enter the number of elements:
10

Enter the array elements :
1 2 3 3 2 4 1 4 4 5 

Sorted Array based on its frequency:
 4   4   4   2   2   3   3   1   1   5

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