numJewelsInStones.js

/**

https://leetcode.com/problems/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".

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.

 * @param {string} J
 * @param {string} S
 * @return {number}
 */
 
var numJewelsInStones = function(J, S) {
    let map = {};
    let count = 0;
    for (let i = 0; i < J.length; i++) {
        map[J[i]] = true;
    }
    for (let i = 0; i < S.length; i++) {
        if (map[S[i]]) {
            count++;
        }
    }
    return count;
};