Permutations II

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].

Runtime: 28ms

class Solution {
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<vector<int> > result;
        if(nums.empty()) return result;
        
        helper(result, nums, 0, nums.size() - 1);
        return result;
    }
    
    void helper(vector<vector<int> >& result, vector<int>& nums, int depth, int n){
        if(depth == n){
            result.push_back(nums);
            return;
        }
        
        for(int i = depth; i < nums.size(); i++){
            if(noSwap(nums, depth, i)) continue;
            
            swap(nums[depth], nums[i]);
            helper(result, nums, depth + 1, n);
            swap(nums[depth], nums[i]);
        }
    }
    
    bool noSwap(vector<int>& nums, int depth, int i){
        for(int j = depth; j < i; j++){
            if(nums[j] == nums[i])
                return true;
        }
        return false;
    }
};