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 permute(set<vector<int> >& numSet,vector<int> &num,int begin){
if(begin==num.size()-1){
numSet.insert(num);
return;
}
permute(numSet,num,begin+1);

for(int i=begin+1;i<num.size();i++){
if(num[begin]!=num[i]){
vector<int> a(num);
int tmp=a[begin];
a[begin]=a[i];
a[i]=tmp;
permute(numSet,a,begin+1);
}
}
}

vector<vector<int> > permuteUnique(vector<int> &num) {
vector<vector<int> > result;
set<vector<int> > numSet;
if(num.empty()||num.size()==0){
return result;
}
permute(numSet,num,0);
result.assign(numSet.begin(),numSet.end());
return result;
}
};