Leetcode -- permutations II

Problem description:

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

For example,
[1,1,2]Have the following unique permutations:
[1,1,2],[1,2,1], And[2,1,1].

Analysis: the question refers to printing all the arrays of repeated numbers. You can use a judgment function to determine whether the previous occurrence has occurred at any time. The Code is as follows:

class Solution {public:        void swap(int &a,int &b)    {        int temp=a;        a=b;        b=temp;    }        bool Isduplicate(vector<int> num,int begin,int last)    {        for(vector<int>::size_type i=begin;i!=last;++i)            if(num[i]==num[last])                return false;        return true;    }            void permutations(vector<int> num,int begin,vector<int> &permutation,vector<vector<int> > &res)    {        if(begin==num.size())        {            res.push_back(permutation);            return;        }                for(vector<int>::size_type index=begin;index!=num.size();++index)        {                        if(Isduplicate(num,begin,index))            {            swap(num[begin],num[index]);            permutation.push_back(num[begin]);            permutations(num,begin+1,permutation,res);            permutation.pop_back();            swap(num[begin],num[index]);            }                    }    }    vector<vector<int> > permuteUnique(vector<int> &num) {        vector<vector<int> > res;        if(num.empty())            return res;        vector<int> permutation;        permutations(num,0,permutation,res);        return res;    }};

Leetcode -- permutations II