先一路走到黑，然后再一步一步往回走。回溯没毛病。

class Solution {public:    vector
     
      
       > res;       vector
       
        
         > subsetsWithDup(vector
         
          & nums) {         if(nums.empty()){            return res;        }     set
          
           
            > temp; vector
            
              ans; dfs(0,nums,temp,ans); for(auto ff:temp) { res.push_back(ff); } return res; } void dfs(int pos,vector
             
               num, set
              
               
                >& filter ,vector
                
                  ans) { if(pos==num.size()) { sort(ans.begin(), ans.end()); filter.insert(ans); return; } dfs(pos+1,num,filter,ans); ans.push_back(num[pos]); dfs(pos+1,num,filter,ans); }};