vector<vector<int>> permute(vector<int>& nums) {
vector <vector<int>> result;
if(nums.size() == 0)
return result;
permute_helper(0,nums,result);
return result;
}
void permute_helper(int begin,vector<int> &num,vector<vector<int>> &result){
if(begin >= num.size()){
result.push_back(num);
return;
}
for(int i = begin;i < num.size();i++){
swap(num[i],num[begin]);
permute_helper(begin+1,num,result);
swap(num[i],num[begin]);
}
}
vector<vector<int> > permute_helper(vector<int> &num, int n){
vector<vector<int> > result;
if(n==0)
return result;
if(n==1){
vector<int> t;
t.push_back(num[0]);
result.push_back(t);
return result;
}
vector<vector<int> > pre_result = permute_helper(num, n-1);
std::vector<int>::iterator it;
for(int i=0;i<pre_result.size();i++){
for(int j=0;j<=pre_result[i].size();j++){
vector<int> t;
t = pre_result[i];
it = t.begin();
t.insert(it+j, num[n-1]);
result.push_back(t);
}
}
}
vector<vector<int> > permute(vector<int> &num) {
return permute_helper(num, num.size());
}
