[78] 子集

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var subsets = function (nums) {
  const result = [[]]
  for (let i = 0; i < nums.length; i++) {
    for (let j = result.length - 1; j >= 0; j--) {
      result.push([...result[j], nums[i]])
    }
  }
  return result
};