前端小白的江湖路

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var subsets = function(nums) {
  let result = [[], ],
    start,
    end;

  for(let i=0; i<nums.length; ++i) {
    result.push([nums[i]]);
  }

  start = 1,
  end = result.length-1;
  for(let m = 0; m<nums.length-1; ++m) {
    end = result.length - 1;
    while(start <= end) {
      let n = nums.indexOf(result[start][result[start].length-1]) + 1;
      for(let i=n; i<nums.length; ++i) {
        result.push([...result[start], nums[i]]);
      }
      start++;
    }
  }
  return result;
};

var subsets = function (nums) {
  let result = [[]];
  for(let i=0; i<nums.length; ++i) {
    let len = result.length;
    for(let j=0; j<len; ++j) {
      result.push([...result[j], nums[i]]);
    }
  }
  return result;
}