Recursion: Count Vowels

Write a function that recursively returns the number of vowels in a string.

Examples

countVowels("apple") ➞ 2

countVowels("cheesecake") ➞ 5

countVowels("bbb") ➞ 0

countVowels("") ➞ 0

Notes

• All letters will be in lower case.
• Vowels are: a, e, i, o, u.