Leetcode: Permutations

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 get(vector<int> &num, int index, vector<vector<int>> &solution)
{
if(index >= num.size())
{
solution.push_back(num);
return;
}else
for(int i = index; i < num.size(); i++)
{
swap(num[index],num[i]);
get(num,index+1,solution);
swap(num[index],num[i]);
}
}
vector<vector<int>> permute(vector<int> &num) {
// Note: The Solution object is instantiated only once.
vector<vector<int>> solution;
if(num.size()<1)return solution;
get(num, 0, solution);
return solution;
}