Permutations [LeetCode]

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].

Notes: recursive, in place.

 class Solution {
 public:
     vector<vector<int> > permute(vector<int> &num) {
         int size = num.size();
         vector<vector<int> > result;
         if(size == )
             return result;
         if(size == ) {
             vector<int> per;
             per.push_back(num[]);
             result.push_back(per);
             return result;
         }

         for(int i = ; i < size; i ++) {
             int current = num[i];
             num.erase(num.begin() + i);
             vector<vector<int> > ret = permute(num);
             num.insert(num.begin() + i, current);
             for(auto item: ret) {
                 item.insert(item.begin(), current);
                 result.push_back(item);
             }
         }
         return result;
     }
 };