You are given a string `s` of even length. Split this string into two halves of equal lengths, and let `a` be the first half and `b` be the second half.

Two strings are alike if they have the same number of vowels (`'a'`, `'e'`, `'i'`, `'o'`, `'u'`, `'A'`, `'E'`, `'I'`, `'O'`, `'U'`). Notice that `s` contains uppercase and lowercase letters.

Return `true` if `a` and `b` are alike. Otherwise, return `false`.

Example 1:

    Input: s = "book"
    Output: true
    Explanation: a = "bo" and b = "ok". a has 1 vowel and b has 1 vowel. Therefore, they are alike.

Example 2:

    Input: s = "textbook"
    Output: false
    Explanation: a = "text" and b = "book". a has 1 vowel whereas b has 2. Therefore, they are not alike.
    Notice that the vowel o is counted twice.

Constraints:

- `2 <= s.length <= 1000`
- `s.length` is even.
- `s` consists of uppercase and lowercase letters.