[leetcode-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 Sis 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.

思路：

用map统计，扫描一遍S即可。

int numJewelsInStones(string J, string S)
{
    int ret = 0;
    map<char,int>mp;
    for(auto ch : S)mp[ch]++;
    
    for(int i= 0;i<J.size();j++)
    {
        ret += mp[J[i]];
    }
    return ret;
}