Count Vowels in String

Given a string s, count how many characters are English vowels (a, e, i, o, u). Matching is case-insensitive, so uppercase vowels also count. Return the count…

Given a string `s`, count how many characters are English vowels (`a`, `e`, `i`, `o`, `u`). Matching is case-insensitive, so uppercase vowels also count. Return the count as an integer. Spaces, digits, and symbols do not add to the count.

- `0 <= s.length <= 10^5` - `s` contains printable ASCII characters. - Vowels are `a`, `e`, `i`, `o`, `u`, matched case-insensitively. - An empty string has a vowel count of `0`. - The interactive visualizer accepts `0 <= s.length <= 40`; longer valid judge inputs remain execution-only.

Example 1: input s = "education"; output 5. The vowels are e, u, a, i, and o — five in total, so the count is 5.

Example 2: input s = "rhythm"; output 0. None of the characters in rhythm are vowels, so the count is 0.

Example 3: input s = "AEIOU"; output 5. All five characters are uppercase vowels. Matching is case-insensitive, so every one is counted.

Category: Strings. Topic: strings. Difficulty: Easy. Patterns: hashing.