【LeetCode】 771. Jewels and Stones

Description

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".

Note:

• S and J will consist of letters and have length at most 50.
• The characters in J are distinct.

你有一段字串J代表有哪些石頭的種類是珠寶，還有一段字串S代表你有哪些石頭。每一個在S裡面的字元是代表你有的石頭的種類。你想要知道你有的石頭之中有多少珠寶。

這些在J裡面的字母都不相同，並且在J和S裡面的字元一定是字母。字母的大小寫是需要在意的，所以a和A被視為是不同種類的石頭。

注意：

• S 和 J 只包含字母且長度不超過50。
• J 裡面的字元都不相同。

Example:

Example 1:

Input: J = "aA", S = "aAAbbbb"
Output: 3


Example 2:

Input: J = "z", S = "ZZ"
Output: 0

Solution

• 用一個hash去紀錄J裡面出現的字。
• 再用一個迴圈去比對S的字是否出現在hash裡面。

Code

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        unordered_set<char> hash;
        int count = 0;
        for(int i = 0; i < J.length(); i++)
            hash.insert(J[i]);
        for(int j = 0; j < S.length(); j++)
            if(hash.count(S[j])) 
                count++;
        return count;
    }
};

tags: LeetCode C++