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Recursion for Coding Interviews in C++

Count the Number of Occurrences of a Number in an Array

Explore how to implement and understand a recursive function in C++ that counts the number of times a given number appears in an array. This lesson guides you through the base and recursive cases, enhancing your problem-solving skills with recursion applied to arrays.

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Total Occurrences of a Number

The number of occurrences of a number means the frequency by which a number n appears in the array.

The following illustration clears the concept:

Implementing the Code

The following code explains how to find the frequency of a number in an array using recursion.

Experiment with the code by changing the values of array and num to see how it works!

C++
#include<iostream>
using namespace std;
// Recursive Function
int  NoOfOccurrence(int array[], int size, int num)
{
    int found = 0;
   //base case
    if (size< 0) //if the whole array has been traversed
        return 0;
    if (array[size] == num)// check if element is found
        ++found;// increment found
   //recursive case
    return (found + NoOfOccurrence(array, size- 1, num));
}
// Driver Function
int main() {
  int array[7] = {2,3,4,1,7,8,3};//define an array
  int size=7;//define the size of array
  int num=3;// define the number whose frequency of occurrence is to be found
  cout<<"Number of occurrences of "<<num<<" : ";
  cout << NoOfOccurrence( array, size-1,num);//call recursive function
  return 0;
}

Understanding the Code

A ...