119. 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?

---

public class Solution {
    public ArrayList<Integer> getRow(int rowIndex) {
         
        ArrayList<Integer> rst = new ArrayList<Integer>();

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