class Solution {
    public int numJewelsInStones(String jewels, String stones) {
        int m = jewels.length(), n = stones.length();
        Set<Character> set = new HashSet<>();
        for (int i = 0; i < m; i++) {
            set.add(jewels.charAt(i));
        }
        int res = 0;
        for (int i = 0; i < n; i++) {
            if (set.contains(stones.charAt(i))) {
                res++;
            }
        }
        return res;
    }
}