Solution: Jewels and Stones

Statement

You are given two strings, jewels and stones. Each character in jewels represents a stone type that is a jewel, and each character in stones represents a stone you have. Count how many characters in stones belong to the set of characters in jewels.

Note: Matching is case-sensitive, so 'a' and 'A' are different types of stones.

Constraints:

• $1\le$ ...