771. Jewels and Stones

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

The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so "a" is considered a different type of stone from "A".

(1) -> 常常出现在函数名后面，描述函数的返回类型，如：

def add(x,y)->int: #函数的返回类型为int

    return x+y

（2）@property是一个装饰器，能够使得类把一个方法变成属性调用。如：

class Student(object):

    @property

    def score(self):

        return self._score

    @score.setter

    def score(self,value):

        if not isinstance(value,int):

            raise ValueError('score must be an integer!')

        if score<0 or score>100:

            raise ValueError('score must between 0~180')

        self._score = value

s = Student()

s.score = 60

s.score = 9999 #ValueError

（3）解题：

class Solution:
    def numJewelsInStones(self, J:'str', S:'str') -> 'int':
        num = 0
        for s in S:
            if s in J:
                num += 1
        return num

s = Solution()
n = s.numJewelsInStones("z","ZZ")
print(n)

 优化：    

class Solution:
    def numJewelsInStones(self, J:'str', S:'str') -> 'int':
        return sum(s in J for s in S)

s = Solution()
n = s.numJewelsInStones("z","ZZ")
print(n)

#方法二：使用str的count属性
def numJewelsInStones(self, J:'str', S:'str') -> 'int':
        return sum(map(S.count,J))