此题与823排列https://www.acwing.com/problem/content/825/类似
class Solution {
public:
vector<vector<int>> permutation(vector<int>& nums) {
sort(nums.begin(),nums.end());
vector<vector<int>> res;
do{
res.push_back(nums);
}while(next_permutation(nums.begin(),nums.end()));
return res;
}
};