771. Jewels and Stones 
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Problem
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 <= 50jewelsandstonesconsist of only English letters.- All the characters of
jewelsare unique.