771. Jewels and Stones

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.

// Hashset
int numJewelsInStones(string J, string S) { // time: O(m + n); space: O(n)
    unordered_set<char> jewel(J.begin(), J.end());
    int res = 0;
    for (char c : S) {
        if (jewel.count(c)) ++res;
    }
    return res;
}

// Use boolean array to serve as an unordered_set
int numJewelsInStones(string J, string S) { // time: O(m + n); space: O(1)
    vector<bool> jewel(128, false);
    for (char c : J) jewel[c] = true;
    int res = 0;
    for (char c : S) {
        if (jewel[c]) ++res;
    }
    return res;
}