Understanding the Frequency Counter Program in C++

This is a program designed to calculate frequency for each distinct element in the array. Since we use just a simple counter mechanism, this determines how often each element may appear in an array. Please see below the code and in detail how exactly the code works:

#include<iostream>
using namespace std;

void freq(int *arr, int n){
    int count[100];

    for(int i = 0; i < n; i++){
        count[i] = 0;
    }

    for(int i = 0; i < n; i++){
        int idx = arr[i];
        if (count[idx] == 0){

        count[idx] = 1;
        }else{
            count[idx]++;
        }

    }
    for(int i = 0; i < n; i++){
        if(count[i] != 0){

        cout<<i<<"="<<count[i]<<endl;
        }
    }
}

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

    freq(arr,n);
}

Code Breakdown and Explanation

Header File:

Frequency Calculation Function:

void freq(int *arr, int n) {
    int count[100];

Parameters
arr: A pointer to the given input array.
n: The length of the array.

Frequency Array (count):
This array holds the count of each element.
It is initialized to size 100, assuming that array values will not exceed this range.

Initializing the Frequency Array:

for (int i = 0; i < n; i++) {
    count[i] = 0;
}

Each element of the count array is set to 0 to ensure accurate counting.

Counting Element Frequencies:

for (int i = 0; i < n; i++) {
    int idx = arr[i];
    if (count[idx] == 0) {
        count[idx] = 1;
    } else {
        count[idx]++;
    }
}

Index Mapping:
The value of each element in arr is used as an index in the count array.
Incrementing Count:
If the value at count[idx] is 0, it is initialized to 1.
Otherwise, it is incremented by 1.

Printing the Frequencies:

for (int i = 0; i < n; i++) {
    if (count[i] != 0) {
        cout << i << "=" << count[i] << endl;
    }
}

The program iterates over the count array to print the frequency of each element that occurs in the input array.

Main Function:

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

Input Array:
It contains the integers whose frequencies are to be computed.
Computing Frequencies:
It invokes the freq function with the array and its size as arguments.

Example Run
Input Array:

arr[] = {1, 4, 1, 3, 2, 4, 3}

Step-by-Step Run:

Set the count array to zeros.
For each element in arr, update its corresponding index in count.
Traverse the count array and display non-zero frequencies.
Output:

1=2
2=1
3=2
4=2

Key Concepts in the Program
Frequency Calculation:

A direct mapping between the value of an element and its index in the count array enables efficient counting.

Space Efficiency:

The program uses an auxiliary array (count) to store frequencies, with a size of 100 for simplicity.
However, this can be optimized to fit the range of elements in the input array.

Edge Cases:

The program assumes all elements are positive integers within the range of 0 to 99.
For a broader range, modifications to the count array size are necessary.
Optimization Suggestions

Dynamic Range Adjustment:
Instead of a fixed-size count array, dynamically adjust its size based on the maximum value in the input array.

Why This Program is Useful
Simplicity:
The logic is quite straightforward and, therefore easily understandable even for beginners.

Practical Application
Frequency counting is extensively used in data analysis, histograms, and pattern recognition.