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].

class Solution {
public:
    std::vector<std::vector<int> > permuteUnique(std::vector<int> &num) {
		std::set<std::vector<int>> s;
		std::vector<std::vector<int>> res;
		std::sort(num.begin(),num.end());
		do
		{
			s.insert(num);
		} while (std::next_permutation(num.begin(),num.end()));
		for(std::set<std::vector<int>>::iterator it = s.begin(); it != s.end(); it++)
		{
			res.push_back(*it);
		}
		return res;
    }
};

leetcode - Permutations II