Problem 8: Count Vowels

Hey everyone! 👋

Today, we're tackling a string manipulation problem: Counting Vowels.

The Problem

The goal is to write a function that counts the number of vowels in a given string. We need to consider both lowercase and uppercase vowels ('a', 'e', 'i', 'o', 'u').

Example:

• count_vowels("hello world") should return 3
• count_vowels("AEIOU") should return 5

The Solution

Here is the Python implementation:

def count_vowels(s):
    """
    Counts the number of vowels in a string.
    """
    vowels = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}
    count = 0
    for char in s:
        if char in vowels:
            count += 1
    return count

# Test case
print(count_vowels("pooopcycle"))
# Output: 4

Code Breakdown

Let's walk through the code line by line:

1. def count_vowels(s):

   • Defines a function named count_vowels that takes one parameter s (a string).

2. vowels = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}

   • Creates a set containing all vowels (both lowercase and uppercase).
   • Using a set allows for efficient O(1) lookups.

3. count = 0

   • Initializes a counter variable count to 0.

4. for char in s:

   • Iterates through each character in the input string s.

5. if char in vowels:

   • Checks if the current character exists in the vowels set.

6. count += 1

   • If the character is a vowel, increments the count by 1.

7. return count

   • Returns the final count of vowels.

Example Walkthrough with "pooopcycle"

1. char is 'p', not in vowels.
2. char is 'o', in vowels -> count becomes 1.
3. char is 'o', in vowels -> count becomes 2.
4. char is 'o', in vowels -> count becomes 3.
5. char is 'p', not in vowels.
6. char is 'c', not in vowels.
7. char is 'y', not in vowels.
8. char is 'c', not in vowels.
9. char is 'l', not in vowels.
10. char is 'e', in vowels -> count becomes 4.
11. Returns 4.

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Happy coding! 💻