771. 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

Note:

• S and J will consist of letters and have length at most 50.
• The characters in J are distinct.

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        int res=0;
              map<char,int> m;
              for(auto a:J){
                  m[a]++;
              }
              for(auto a:S){
                  if(m[a]!=0) res++;
              }
              return res;
  
    }
};