Count the Number of Zeros in an Array

Problem Statement

Given an array of integers, the task is to count how many elements in the array are equal to zero (0).

This problem focuses on:

• Traversing the entire array
• Comparing each element with a given value
• Maintaining a frequency count

Why This Problem Is Important

This problem helps you understand:

• Frequency counting in arrays
• Conditional checks during traversal
• Basics of data analysis
• Preparation for hashing and counting problems

Counting specific values is commonly used in:

• Data cleaning
• Compression algorithms
• Sparse arrays
• Statistical analysis

Input and Output Format

Input

Array: [0, 1, 0, 3, 0, 5]

Output

Number of zeros = 3

Key Concept

We scan each element of the array and increase a counter whenever the element is 0.

Approach / Logic

1. Initialize a variable count = 0
2. Traverse the array
3. If the current element equals 0, increment count
4. After traversal, print count

Step-by-Step Algorithm

1. Start
2. Read the array and its size
3. Initialize count = 0
4. Loop from index 0 to n - 1
5. If arr[i] == 0, increment count
6. Print count
7. End

Pseudocode

count = 0
for i = 0 to n-1:
    if arr[i] == 0:
        count = count + 1
print count

Dry Run Example

Array = [0, 4, 0, 7, 9, 0]

i = 0 → arr[i] = 0 → count = 1
i = 1 → arr[i] = 4 → no change
i = 2 → arr[i] = 0 → count = 2
i = 3 → arr[i] = 7 → no change
i = 4 → arr[i] = 9 → no change
i = 5 → arr[i] = 0 → count = 3

Final Count = 3

Time and Space Complexity

Language-wise Implementation

C Implementation

#include 

int main() {
    int arr[] = {0, 1, 0, 3, 0, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    int count = 0;

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

    printf("Number of zeros in the array: %d", count);
    return 0;
}

Output

Number of zeros in the array: 3

C++ Implementation

#include 
using namespace std;

int main() {
    int arr[] = {0, 1, 0, 3, 0, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    int count = 0;

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

    cout << "Number of zeros in the array: " << count;
    return 0;
}

Output

Number of zeros in the array: 3

Java Implementation

public class Main {
    public static void main(String[] args) {
        int[] arr = {0, 1, 0, 3, 0, 5};
        int count = 0;

        for(int num : arr) {
            if(num == 0) {
                count++;
            }
        }

        System.out.println("Number of zeros in the array: " + count);
    }
}

Output

Number of zeros in the array: 3

Python Implementation

arr = [0, 1, 0, 3, 0, 5]
count = 0

for num in arr:
    if num == 0:
        count += 1

print("Number of zeros in the array:", count)

Output

Number of zeros in the array: 3

C# Implementation

using System;

class Program {
    static void Main() {
        int[] arr = {0, 1, 0, 3, 0, 5};
        int count = 0;

        foreach(int num in arr) {
            if(num == 0) {
                count++;
            }
        }

        Console.WriteLine("Number of zeros in the array: " + count);
    }
}

Output

Number of zeros in the array: 3

JavaScript Implementation

let arr = [0, 1, 0, 3, 0, 5];
let count = 0;

for (let i = 0; i < arr.length; i++) {
    if (arr[i] === 0) {
        count++;
    }
}

console.log("Number of zeros in the array:", count);

Output

Number of zeros in the array: 3

Common Mistakes to Avoid

• Using assignment (=) instead of comparison (== or ===)
• Forgetting to initialize the counter
• Breaking the loop early
• Confusing zero with null or empty values

Interview Variations

• Count occurrences of a given number
• Count zeros and non-zeros separately
• Move all zeros to the end of the array
• Count zeros using hashing

Detailed Summary

Counting the number of zeros in an array is a classic frequency-counting problem that strengthens understanding of array traversal and conditional logic. By iterating through the array once and evaluating each element, we efficiently determine how often a specific value appears. This problem forms the foundation for more advanced topics such as hashing, frequency maps, and optimized data processing techniques used in real-world applications.

Next Problem in the Series

Find the Second Largest Element in an Array