771__easy__jewels-and-stones.js

/*

	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) {
  if (!J || !S) return 0;

  let count = 0;
  let set = new Set();

  for (let i = 0; i < J.length; i++) {
    set.add(J[i]);
  }
  for (let i = 0; i < S.length; i++) {
    if (set.has(S[i])) count++;
  }
  return count;
};
/**
 *
 * O(J.length + S.length) time
 * O(J.length) space
 *
 * 3m
 */