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;
    }
};