leetcode[47]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:

bool isSwap(vector<int> &num, int i, int j)

{

    int ii=i;

    while(num[ii]!=num[j]&&ii<j)ii++;

    if (ii==j)return true;

    else return false;

}

void perm(vector<int> &num, int i, int N, vector<vector<int>> &res)

{

    if(i==N)

        res.push_back(num);

    for (int j=i;j<N;j++)

    {

        if (!isSwap(num,i,j))continue;

        swap(num[i],num[j]);

        perm(num,i+1,N,res);

        swap(num[j],num[i]);

    }

}

vector<vector<int> > permuteUnique(vector<int> &num) 

{

    vector<vector<int> > res;

    sort(num.begin(),num.end());

    perm(num,0,num.size(),res);

    return res;

}

};