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

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.

題解：

class Solution {
public:
  int numJewelsInStones(string J, string S) {
    int j = J.size();
    int s = S.size();
    if (j == 0 || s == 0) {
      return 0;
    }
    int ans = 0;
    map<char, bool> dic;
    for (int i = 0; i < j; i++) {
      dic.insert(pair<char, bool>(J[i], true));
    }
    for (int i = 0; i < s; i++) {
      if (dic.find(S[i]) != dic.end()) {
        ans++;
      }
    }
    return ans;
  }
};