leetcode - Permutations

Given a collection of numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

class Solution {
public:
    std::vector<std::vector<int> > permute(std::vector<int> &num) {
		std::vector<std::vector<int>> res;
		std::sort(num.begin(),num.end());
		do
		{
			res.push_back(num);
		} while (std::next_permutation(num.begin(),num.end()));
		return res;
    }
};