vector<vector<int>> subset;
 
  void gen(vector<int>& nums,int i,vector<int> sub)
  {
     if(i==nums.size())
        {
            subset.push_back(sub);
            return;
        }
        gen(nums,i+1,sub);

        sub.push_back(nums[i]);
        gen(nums,i+1,sub);

        
  }