This idea is very easy, don't have to sort, just add a hash on answer of https://leetcode.com/problems/permutations

```
class Solution {
private:
void permuteHelp(vector<vector<int>> &r, vector<int> &nums, int k) {
if (k >= nums.size() - 1) {
r.push_back(nums);
return;
}
unordered_map<int, bool> m;
for (int i = k; i < nums.size(); ++i) {
if (m[nums[i]])
continue;
m[nums[i]] = true;
swap(nums[k], nums[i]);
permuteHelp(r, nums, k+1);
swap(nums[k], nums[i]);
}
}
public:
vector<vector<int>> permuteUnique(vector<int>& nums) {
vector<vector<int>> r;
permuteHelp(r, nums, 0);
return r;
}
};
```