[Leetcode] 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?

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> getRow(int rowIndex) {
        ArrayList<Integer> result = new ArrayList<Integer>();
        if(rowIndex < 0) return result;
        result.add(1);
        for(int i = 0; i < rowIndex; i++){
            for(int j = result.size() - 1; j >= 1; j--){
                result.set(j, result.get(j) + result.get(j - 1));
            }
            result.add(1);
        }
        return result;
    }
}