771. Jewels and Stones*

771. Jewels and Stones*

​​https://leetcode.com/problems/jewels-and-stones/​​

题目描述

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.

C++ 实现 1

题意本质上是讲 ​​S​​​ 中有多少个字符在 ​​J​​ 中出现过, 字符大小写敏感.

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        unordered_set<char> record(J.begin(), J.end());
        int count = 0;
        for (auto &c : S)
            if (record.count(c))
                count ++;
        return count;
    }
};