leetcode 90: Subsets II

class Solution {
public:
vector<vector<int>> subsetsWithDup(vector<int>& nums) {
vector<int> set;
vector<vector<int> > res;
sort(nums.begin(),nums.end());
helper(nums,set,res,0);
return res;
}
void helper(vector<int>& nums, vector<int>& set, vector<vector<int> >& res, int start)
{
res.push_back(set);
for(int i=start;i<nums.size();i++)
{
if(i==start||nums[i]!=nums[i-1])
{
set.push_back(nums[i]);
helper(nums,set,res,i+1);
set.pop_back();
}
}
}
};