数组中找几个和为sum 且 不重复

class Solution {
public:
    vector<vector<int> > combinationSum2(vector<int> &num, int target) {
        vector<int> ivec;
        vector<vector<int> > res;
        if(num.size()==0||target<=0){
            return res;
        }
        sort(num.begin(),num.end());
        dfs(num,0,target,ivec,res);
        res.clear();
        set<vector<int> >::iterator iter;
        for(iter=z.begin();iter!=z.end();iter++){
            res.push_back(*iter);
        }
        return res;
    }
    set<vector<int> > z;  //利用了set去重
    void dfs(vector<int> &nums,int k,int target,vector<int> ivec,vector<vector<int> > &res){
        if(target==0){
            res.push_back(ivec);
            z.insert(ivec);
            return ;
           
        }else if(target<0){
            return ;
        }
        for(int i=k;i<nums.size();++i){
            ivec.push_back(nums[i]);
            dfs(nums,i+1,target-nums[i],ivec,res);
            ivec.pop_back();
        }
    }
};