771. Jewels and Stones

class Solution(object):
    def numJewelsInStones(self, jewels, stones):
        """
        :type jewels: str
        :type stones: str
        :rtype: int
        """
        jewels_set = set()
        for i in range(len(jewels)):
            jewels_set.add(jewels[i])
        
        counter = 0
        for i in range(len(stones)):
            if stones[i] in jewels_set:
                counter += 1

        return counter