Up and Down - codepath/compsci_guides GitHub Wiki

TIP102 Unit 1 Session 1 Standard (Click for link to problem statements)

Problem Highlights

  • 💡 Difficulty: Easy
  • ⏰ Time to complete: 5 mins
  • 🛠️ Topics: Lists, Loops, Counting

U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

  • Q: What should the function return if the list is empty?

    • A: The function should return 0 since there are no numbers to count.

  • Q: How does the function handle the counting of odd and even numbers?

    • A: The function increments counters for odd and even numbers as it iterates through the list.

  • The function up_and_down(lst) should return the difference between the number of odd numbers and the number of even numbers in the list.

HAPPY CASE
Input: lst = [1, 2, 3]
Expected Output: 1

Input: lst = [1, 3, 5]
Expected Output: 3

Input: lst = [2, 4, 10, 2]
Expected Output: -4

EDGE CASE
Input: []
Expected Output: 0

Input: [3]
Expected Output: 1

Input: [2]
Expected Output: -1

P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Iterate through the lst list, count the odd and even numbers, and then return the difference.

1. Define the function `up_and_down(lst)`.
2. Initialize counters `odd_count` and `even_count` to 0.
3. Use a loop to iterate through each number in `lst`.
4. For each number, check if it is odd or even using modulus division.
5. Increment the appropriate counter based on the result.
6. Calculate the difference by subtracting `even_count` from `odd_count`.
7. Return the difference.

⚠️ Common Mistakes

  • Forgetting to initialize the counters.
  • Incorrectly calculating the difference.

I-mplement

Implement the code to solve the algorithm.

def up_and_down(lst):
    # Initialize counters for odd and even numbers
    odd_count = 0
    even_count = 0
    
    # Iterate through the list of numbers
    for num in lst:
        # Check if the number is odd
        if num % 2 != 0:
            odd_count += 1
        else:
            even_count += 1
    
    # Calculate the difference between odd and even counts
    difference = odd_count - even_count
    
    # Return the difference
    return difference