771

771. Jewels and Stones (Easy)

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.

Solution 1.

// OJ: https://leetcode.com/problems/jewels-and-stones/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    int numJewelsInStones(string J, string S) {
        unordered_set<char> s(J.begin(), J.end());
        int ans = 0;
        for (char c : S) ans += s.count(c);
        return ans;
    }
};