題目

難度：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.

第一次解法

/**
 * @param {string} J
 * @param {string} S
 * @return {number}
 */
var numJewelsInStones = function(J, S) {
    var num = 0;
    var l = S.length;
    while(l>0){
        if(J.indexOf(S.charAt(l-1))>-1){
            num++
        }
        l--
    }
    return num
};
# runtime : 75ms