Counting Odd and Even Occurrences in an Array

Introduction:

In programming, it’s common to encounter scenarios where you need to count the number of elements occurring an odd number of times and the number of elements occurring an even number of times in an array. This tutorial will guide you through the process of solving such a problem efficiently using Python.

Understanding the Problem:

Given an array of integers, our task is to count the number of elements that occur an odd number of times and the number of elements that occur an even number of times. We need to iterate through the array, calculate the frequency of each element, and then determine whether the frequency is odd or even.

Efficient Solution Approach:

To efficiently solve this problem, we can follow these steps:

1. Create a dictionary to store the frequency of each element in the array.
2. Iterate through the array and update the frequency count in the dictionary.
3. Count the number of elements with odd and even frequencies.
4. Print the counts of odd and even occurring elements.

Implementation in Python:

def count_even_odd(T, test_cases):
    for arr in test_cases:
        frequency = {}
        for num in arr:
            if num in frequency:
                frequency[num] += 1
            else:
                frequency[num] = 1

        odd_count = 0
        even_count = 0
        for key, value in frequency.items():
            if value % 2 == 0:
                even_count += 1
            else:
                odd_count += 1

        print(odd_count, even_count)

# Main function
if __name__ == "__main__":
    T = int(input())  # Number of test cases
    test_cases = []
    for _ in range(T):
        N = int(input())  # Length of the array
        ARR = list(map(int, input().split()))  # Array elements
        test_cases.append(ARR)

    count_even_odd(T, test_cases)  # Find and print counts of even and odd occurring elements

Explanation:

• We define a function count_even_odd that takes the number of test cases and a list of test cases as input.
• Within this function, we create a dictionary frequency to store the frequency of each element in the array.
• We then iterate through each test case, update the frequency count in the dictionary, and count the number of elements with odd and even frequencies.
• Finally, we print the counts of odd and even occurring elements for each test case.

Conclusion:

By following the efficient solution approach outlined in this tutorial, you can easily count the number of elements occurring an odd number of times and the number of elements occurring an even number of times in an array using Python. This knowledge can be applied to various programming problems requiring frequency counting and is essential for enhancing your problem-solving skills. Happy coding!