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]

.

class Solution {
public:

void permute(vector<vector<int> >& result,vector<int>& num,int begin){
if(begin==num.size()-1){
result.push_back(num);
return;
}
for(int i=begin;i<num.size();i++){
vector<int> a(num);
int tmp=a[begin];
a[begin]=a[i];
a[i]=tmp;
permute(result,a,begin+1);
}
}

vector<vector<int> > permute(vector<int> &num) {
vector<vector<int> > result;
if(num.empty()||num.size()==0){
return result;
}
permute(result,num,0);
return result;
}
};