[Leetcode] 771. Jewels and Stones 解题报告

题目：

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：

练手题目。不过本题除了用哈希表之外，还可以用二分查找树以及向量等数据结构解决，J中的数量不同，将会导致不同的数据结构具有不同的运行效率。

代码：

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        unordered_set<char> hash;
        for (auto j : J) {
            hash.insert(j);
        }
        int ans = 0;
        for (auto s : S) {
            ans += hash.count(s);
        }
        return ans;
    }
};