Given an index k, return the k^th 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?

//從後向前
    public List<Integer> getRow(int rowIndex) {
        ArrayList<Integer> cur = new ArrayList<Integer>();
        cur.add(1);
        for (int i = 0; i < rowIndex; i++) {

            for (int j = cur.size()-1; j >0; j--) {
                cur.set(j, cur.get(j)+cur.get(j-1));
            }
            cur.add(1);
        }
        return cur;
    }