40. Full arrangement Ⅱ

You can add set, but it is slow.
After reading the solution, this pruning is good. The judgment inside flag [i-1], if flag [i-1] = 1, it means that the previous number has been used in this arrangement, then the same number can be used continuously; if flag [i-1] = 0 This means that the previous number is already in another arrangement. This number can no longer be used, and will be repeated if used.

 vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<vector<int>>ans;
        vector<int>flag(nums.size(),0);
        vector<int>tep;
        sort(nums.begin(),nums.end());
        dfs(ans,nums,flag,tep);
        return ans;
    }
    void dfs(vector<vector<int>>& ans,vector<int> nums,vector<int>& flag,vector<int> tep){
        if(tep.size()==nums.size()){
            ans.push_back(tep);
            return;
        }
        for(int i=0;i<nums.size();i++){
            if(flag[i]==0){
                if(i>0&&nums[i]==nums[i-1]&&flag[i-1]==0){                  
                  continue;
                }
                    flag[i]=1;
                    tep.push_back(nums[i]);
                    dfs(ans,nums,flag,tep);
                    flag[i]=0;
                    tep.pop_back();
            }
        }
    }