###### tags: `Leetcode` `easy` `hash` `python` `c++`

# 771. Jewels and Stones

## [題目連結:] https://leetcode.com/problems/jewels-and-stones/description/

## 題目:
You're given strings ```jewels``` representing the types of ```stones``` that are jewels, and stones representing the stones you have. Each character in ```stones``` is a type of stone you have. You want to know how many of the stones you have are also jewels.

Letters are case sensitive, so ```"a"``` is considered a different type of stone from ```"A"```.

**Example 1:**

Input: jewels = "aA", stones = "aAAbbbb"
Output: 3

**Example 2:**

Input: jewels = "z", stones = "ZZ"
Output: 0

## 解題想法:
* 此題為，判斷stones中哪些char符合jewels中的元素，求其總數
* 用set將jewls包起來再掃描stones逐一判斷即可
* c++: < set >
* 初始化: **set< xxx > obj_name (yyy.begin(), yyy.end());**

## Python:

class Solution(object):
    def numJewelsInStones(self, jewels, stones):
        """
        :type jewels: str
        :type stones: str
        :rtype: int
        """
        res=0
        jew=set(jewels)
        for item in stones:
            if item in jew:
                res+=1
        return res

## C++:

class Solution {
public:
    int numJewelsInStones(string jewels, string stones) {
        //init set
        set<char> jew(jewels.begin(), jewels.end());
        int res=0;
        for (char item: stones){
            if (jew.find(item)!=jew.end())
                res+=1;
        } 
        return res;
    }
};