771. Jewels and Stones-宝石与石头

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.

Solution in python:

class Solution:
    def numJewelsInStones(self, jewels: str, stones: str) -> int:
        aset = set(jewels)
        count = 0
        for char in stones:
            if char in aset:
                count += 1
        return count