Most frequently asked interview question #8 with solution

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 

Solution in C++:

    int numJewelsInStones(string J, string S) {
        
            int count[256]  = {0};
            int  sol        = 0;
            int  iter       = 0;
        for (iter = 0; iter < S.length(); ++iter){
            ++count[S[iter]];
        }
        
        for(iter = 0; iter < J.length(); ++iter){
            sol += count[J[iter]];
        }
        return sol;
    }