Jewels and stones problem

This post is about the “jewels and stones” problem and my attempt to it.

The purpose is to find elements of string “J” in string “S”, it’s like finding some type of jewels in a pile of stones.

For example, here’s the input: J=”aA”, S=”aAAAbB”, so the output should be 4 in this case.

This is a pretty easy one, so I just put my code below. Although the speed of my program is not the fastest, I can’t check the official answer because I don’t have a premium subscription.

class Solution {
    public int numJewelsInStones(String J, String S) {
        int num=0;
        for (int i=0, l=S.length(); i<l; i++){
            char c = S.charAt(i);
            for (int j=0, k=J.length(); j<k; j++){
                if(c==J.charAt(j)){
                    num++;
                    break;
                }
            }
        }
        return num;
    }
}