Count Vowels — C# Coding Problem
Difficulty: easy | Category: string
Problem Description
Given a string `s`, return the number of vowels (`a`, `e`, `i`, `o`, `u`) in the string. The check should be case-insensitive.
Examples
Example 1
Input: s = "hello"
Output: 2
Explanation: 'e' and 'o' are vowels.
Example 2
Input: s = "programming"
Output: 3
Example 3
Input: s = "rhythm"
Output: 0