The basic idea is like inserting the new element in all the possible position.

1: 1

2: 21 12 (insert 2 at 0 and 1)

3: 321 231 213 (insert 3 to 21) 312 132 123 (insert 3 to 12)

and so on.

The idea can be implement in many ways. Since I don't like recursion, (which means I'm not good at recursion) so here is the way to implement with a queue.

```
class Solution {
public:
void print(vector<int> tmp){
for(int i = 0; i < tmp.size(); i++){
cout << tmp[i] << " ";
}
cout << endl;
}
vector<vector<int>> permute(vector<int>& nums) {
int size1 = nums.size(), count = 1;
vector<vector<int>> result;
if(size1 == 0) return result;
vector<int> cur(1,nums[0]);
queue<vector<int>> store;
store.push(cur);
while(count < size1){
int size2= store.size(), i = 0;
while(i < size2){
cur = store.front();
store.pop();
int size3= cur.size();
for(int j = 0; j <= size3; j++){
auto it = cur.insert(cur.begin() + j, nums[count]);
//print(cur);
store.push(cur);
cur.erase(it);
}
i++;
}
count++;
}
while(!store.empty()){
result.push_back(store.front());
store.pop();
}
return result;
}
};
```