Pascal's Triangle II

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,
Return [1,3,3,1].

Note:
Could you optimize your algorithm to use only O(k) extra space?

 1 class Solution {
 2 public:
 3     vector<int> getRow(int rowIndex) {
 4         vector<int> row;
 5         row.push_back(1);
 6         if(rowIndex == 0) return row;
 7         
 8         row.push_back(1);
 9         if(rowIndex == 1) return row;
10         
11         for(int i = 2; i <= rowIndex; i++){
12             vector<int> temp;
13             temp.push_back(1);
14             for(int j = 1; j < i; j++)
15                 temp.push_back(row[j-1] + row[j]);
16             temp.push_back(1);
17             row = temp;
18         }
19         return row;
20     }
21 };