771.宝石与石头

输入: J = "aA", S = "aAAbbbb"
输出: 3

输入: J = "z", S = "ZZ"
输出: 0

func numJewelsInStones(J string, S string) int {
	search := map[byte]bool{}
	res := 0
	for i := 0; i < len(J); i++ {
		search[J[i]] = true
	}

	for i := 0; i < len(S); i++ {
		if _, ok := search[S[i]]; ok {
			res++
		}
	}

	return res
}