leetcode-136 只出现一次的数字

/**
 * @param {number[]} nums
 * @return {number}
 */
var singleNumber = function (nums) {
  const set = new Set();
  for (let i = 0; i < nums.length; i++) {
    if (!set.has(nums[i])) {
      set.add(nums[i]);
    } else {
      set.delete(nums[i]);
    }
  }
  return Array.from(set)[0];
};
// console.log(singleNumber([2, 2, 1]));