学步园

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].

void permute(vector<int> &num, int index, vector<vector<int>> &res)
    {
		if(index>=num.size()){res.push_back(num);return;}
		set<int> swapnum;
		swapnum.insert(num[index]);
		for(int i = index; i < num.size(); i++)
		{
			if(index != i)
			{
				set<int>::iterator it = swapnum.find(num[i]);
				if(it != swapnum.end())
					continue;
				else
					swapnum.insert(num[i]);
			}
			swap(num[index],num[i]);
			permute(num,index+1,res);
			swap(num[index],num[i]);
		}
	}
	vector<vector<int> > permuteUnique(vector<int> &num) {
        // Note: The Solution object is instantiated only once.
		vector<vector<int>> res;
        permute(num,0,res);
        return res;
    }