Pascal's Triangle II -- Leetcode

Question:

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?

Answer:
public class Solution {

    public List<Integer> getRow(int rowIndex) {
        List<Integer> res = new ArrayList<Integer>();
        if（rowIndex <= 0) return res;

        res.add(1);

        for(int i = 1; i <= rowIndex; ++i){
            for(int j = i-2; j >= 0; --j){
                res.set(j+1, res.get(j) + res.get(j+1));
            }
            res.add(1);
        }
        return res;
    }
}