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".

Example 1:

Input: J = "aA", S = "aAAbbbb"
Output: 3

Example 2:

Input: J = "z", S = "ZZ"
Output: 0

思路：就是掃描統計；

class Solution {
    public int numJewelsInStones(String J, String S) {
        HashSet<Character> set = new HashSet<Character>();
        for(int i = 0; i < J.length(); i++) {
            set.add(J.charAt(i));
        }
        int count = 0;
        for(int i = 0; i < S.length(); i++) {
            if(set.contains(S.charAt(i))) {
                count++;
            }
        }
        return count;
    }
}