All Unique Permutations of an array

Given an array arr[] of length n. Find all possible unique permutations of the array.

• Time : O(n!)
• Space : O(n!)

class Solution {
    vector<vector<int>> res;
    void helper(vector<int>& builder, unordered_map<int, int>& freq, int& n) {
        if(builder.size() == n) res.push_back(builder);
        else {
            for(auto p : freq) {
                if(p.second == 0) continue;
                freq[p.first] -= 1;
                builder.push_back(p.first);
                helper(builder, freq, n);
                builder.pop_back();
                freq[p.first] += 1;
            }
        }
    }
public:
    vector<vector<int>> uniquePerms(vector<int> arr ,int n) {
        res.clear();
        unordered_map<int, int> freq;
        
        for(auto& a : arr) freq[a]++;
        
        helper(vector<int>() = {}, freq, n);
        
        sort(begin(res), end(res));
        return res;
    }
};