Finding the Frequency of Elements in an Array

Understanding Frequency Calculation

Finding the frequency of elements in an array involves counting how many times each element appears.

We will explore three different methods to determine element frequency using C.

Method 1: Using Nested Loops

This method iterates through the array and counts occurrences using nested loops.

#include <stdio.h>
#define SIZE 10

void findFrequency(int arr[], int n) {
    int visited[SIZE] = {0};
    for (int i = 0; i < n; i++) {
        if (visited[i] == 1)
            continue;
        int count = 1;
        for (int j = i + 1; j < n; j++) {
            if (arr[i] == arr[j]) {
                count++;
                visited[j] = 1;
            }
        }
        printf("%d appears %d times\n", arr[i], count);
    }
}

int main() {
    int arr[] = {1, 2, 2, 3, 4, 1, 5, 1, 3, 2};
    int n = SIZE;
    findFrequency(arr, n);
    return 0;
}
            

Method 2: Using Sorting

This method sorts the array first and then counts the frequency.

#include <stdio.h>
#include <stdlib.h>
#define SIZE 10

int compare(const void *a, const void *b) {
    return (*(int*)a - *(int*)b);
}

void findFrequency(int arr[], int n) {
    qsort(arr, n, sizeof(int), compare);
    int count = 1;
    for (int i = 1; i < n; i++) {
        if (arr[i] == arr[i - 1]) {
            count++;
        } else {
            printf("%d appears %d times\n", arr[i - 1], count);
            count = 1;
        }
    }
    printf("%d appears %d times\n", arr[n - 1], count);
}

int main() {
    int arr[] = {1, 2, 2, 3, 4, 1, 5, 1, 3, 2};
    int n = SIZE;
    findFrequency(arr, n);
    return 0;
}
            

Method 3: Using Hashing

This method uses a hash table (array) to store frequency counts.

#include <stdio.h>
#define MAX 100

void findFrequency(int arr[], int n) {
    int freq[MAX] = {0};
    for (int i = 0; i < n; i++) {
        freq[arr[i]]++;
    }
    for (int i = 0; i < MAX; i++) {
        if (freq[i] > 0) {
            printf("%d appears %d times\n", i, freq[i]);
        }
    }
}

int main() {
    int arr[] = {1, 2, 2, 3, 4, 1, 5, 1, 3, 2};
    int n = 10;
    findFrequency(arr, n);
    return 0;
}