Problem Pascal's Triangle II

Problem Description:

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?

Solution:

 1     public List<Integer> getRow(int rowIndex) {
 2 List<Integer> row = new ArrayList<Integer>();
 3         List<Integer> preRow = new ArrayList<Integer>();
 4         for (int i = 0; i <= rowIndex; i++) {
 5             preRow.add(1);
 6             row.add(1);
 7         }
 8             for (int i = 0; i <= rowIndex; i++) {
 9             for (int j = 0; j <= i; j++) {
10                 if (j == 0 || j == i) {
11                     row.set(j, 1);
12                 } else {
13                     row.set(j, preRow.get(j-1)+preRow.get(j));
14                 }
15             }
16             List<Integer> temp = preRow;
17             preRow = row;
18             row = temp;
19         }
20
21         return preRow;
22     }

Problem Pascal's Triangle II