The Vowel Hunt

An easy Python interview practice problem on DataDriven. Write the Python and run it against test cases, with instant feedback.

Domain
Python
Difficulty
easy
Seniority
L3
Asked in
Quantiphi

Problem

Given a string, return the count of vowels: characters a, e, i, o, u (case-insensitive).

Just the vowels. All of them.

Example 1

Input:

s = "Hello World"

Output:

3

Example 2

Input:

s = "AEIOU aeiou"

Output:

10

Worked solution and explanation

Why this problem exists in real interviews

This tests basic string iteration with set membership checks. It is a warm-up problem that reveals whether a candidate handles case-insensitivity correctly and uses a set for O(1) lookups.

Break down the requirements

Step 1: Define the vowel set

Include both lowercase vowels: a, e, i, o, u. Convert each character to lowercase before checking.

Step 2: Iterate and count matches

Loop through each character, check membership in the vowel set, and increment a counter.

The solution

Set lookup with case normalization
def count_vowels(s: str) -> int:
    vowels = {'a', 'e', 'i', 'o', 'u'}
    count = 0
    for ch in s:
        if ch.lower() in vowels:
            count += 1
    result = count
    return result

Common follow-up questions