leetcode-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].

class Solution {
public:
    void mute(vector<vector<int> > &v, vector<int> a, int k, vector<int> &num, vector<bool> b)
    {
        int n = num.size();
        if(k == 0)
        {
            v.push_back(a);
            return;
        }
        for(int i = 0; i < n; i++)
        {
            if(b[i] == false)
            {
                if((i != 0)&&(num[i] == num[i-1])&&(b[i-1])) continue;
                a.push_back(num[i]);
                b[i] = true;
                mute(v,a,k-1,num,b);
                b[i] = false;
                a.pop_back();
            }
        }
        
        return;
    }
    
    vector<vector<int> > permuteUnique(vector<int> &num) {
        vector<vector<int> > v;
        int n = num.size();
        sort(num.begin(),num.end());
        vector<int> a;
        vector<bool> IsUsed(n,false);
        if(n == 0)return v;
        mute(v,a,n,num,IsUsed);
        return v;
    }
};