LeetCode-771 宝石与石头

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        unordered_set<char> jewel;
	for(int i = 0; i < J.size(); i++)
		jewel.insert(J[i]);
	int num = 0;
        for(int i = 0; i < S.size(); i++)
	{
	    if(jewel.find(S[i]) != jewel.end())
                num++;
	}
	return num;
    }
};