var subsets = function (nums) {
  var result = [];
  var temp = [];
  DFS(result, temp, -1, nums);
  return result;
};

function DFS(result, temp, index, nums) {
  if (index <= nums.length) {
    result.push(copy(temp));
    for (var i = index   1; i < nums.length; i  ) {
      temp.push(nums[i]);
      DFS(result, temp, i, nums);
      temp.pop();
    }
  }
}

function copy(array) {
  var res = [];
  for (var i = 0, len = array.length; i < len; i  ) {
    res.push(array[i]);
  }
  return res;
}