C++ Recursion: Counting occurrences of an element in an array with recursive function

C++ Recursion: Exercise-11 with Solution

Write a C++ program to implement a recursive function to count the number of occurrences of a specific element in an array of integers.

Sample Solution:

C Code:

// Recursive function to count the number of occurrences of a specific element in an array
#include <iostream>

// Function to count occurrences of a specific element in an array
int countOccurrences(int nums[], int size, int element) {
  // Base case: if the array is empty, return 0
  if (size == 0)
    return 0;

  // Recursive case: if the first element matches the target element,
  // increment the count and recursively search in the rest of the array
  if (nums[0] == element)
    return 1 + countOccurrences(nums + 1, size - 1, element);
  else
    return countOccurrences(nums + 1, size - 1, element);
}

int main() {
  int nums[] = {3, 4, 5, 7, 3, 9, 5, 3, 5, 9, 3, 4, 3, 5};
  int size = sizeof(nums) / sizeof(nums[0]);
  std::cout << "Array elements: " << std::endl;
  // loop through the array elements
  for (size_t i = 0; i < size; i++) {
    std::cout << nums[i] << ' ';
  }

  int element;
  std::cout << "\nCount the number of occurrences of a specific element in the said array:";
  std::cout << "\nInput an element: ";
  std::cin >> element;

  // Count the occurrences of the element using recursion
  int count = countOccurrences(nums, size, element);

  std::cout << "Number of occurrences of " << element << ": " << count << std::endl;

  return 0;
}

Sample Output:

Array elements:
3 4 5 7 3 9 5 3 5 9 3 4 3 5
Count the number of occurrences of a specific element in the said array:
Input an element: 7
Number of occurrences of 7: 1

3 4 5 7 3 9 5 3 5 9 3 4 3 5
Count the number of occurrences of a specific element in the said array:
Input an element: 3
Number of occurrences of 3: 5

Explanation:

In the above exercise,

• The "countOccurrences()" function takes an array (nums), the array size (size), and the target element (element) as parameters.
• It uses recursion to count the number of occurrences of the target element in the array.
• The base case is when the array size becomes 0, in which case the function returns 0.
• In the recursive case, the function checks if the first element of the array matches the target element.
• If it does, the function increments the count by 1 and recursively calls itself with the rest of the array (nums + 1) and the updated size (size - 1).
• If the first element doesn't match the target element, the function recursively calls itself with the rest of the array and the updated size, without incrementing the count.
• The function returns the final count of occurrences.
• The "main()" function initializes an array of integers, accepts the user to enter the element to count its occurrences.
• It calls the "countOccurrences()" function to count the occurrences of the element, and then displays the result.

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Greatest common divisor (GCD) with recursive function.
Next C++ Exercise: Generating all permutations of a string with recursive function.