You're given strings `jewels` representing the types of stones that are jewels, and `stones` representing the stones you have. Each character in `stones` is a type of stone you have. You want to know how many of the stones you have are also jewels.

Letters are case sensitive, so `"a"` is considered a different type of stone from `"A"`.

Example 1:

    Input: jewels = "aA", stones = "aAAbbbb"
    Output: 3

Example 2:

    Input: jewels = "z", stones = "ZZ"
    Output: 0

Constraints:

- `1 <= jewels.length, stones.length <= 50`
- `jewels` and `stones` consist of only English letters.
- All the characters of `jewels` are unique.