Permutation Generation

Given a collection of numbers, return all possible permutations.
For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

void permute(vector<int> num, int i, vector<vector<int> > & result)

{

 if(i >= num.size())

 {

  result.push_back(num);

  return;

 }



 for(int j = i; j < num.size(); j++)

 {

  swap(num[i], num[j]);

     permute(num, j+1, result);

  swap(num[i], num[j]);

    }

}

vector<vector<int> > permute(vector<int> &num) {

     vector<vector<int> > result;

  permute(num, 0, result);

  return result;

}