[leetcode]Pascal's Triangle II

题目描述如下：

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?

杨辉三角的变形，Note说要用O(k)的空间，想到可以用递归完成。

其他也没有什么难度，代码如下：

public class Solution {
    public List<Integer> getRow(int rowIndex) {
        List<Integer> list = new ArrayList<Integer>();
        int i ;
        if(rowIndex == 0) {
            list.add(1);
            return list;
        }else{
            List<Integer> tmplist =  getRow(rowIndex - 1);
            for(i = 0; i < rowIndex + 1; i++){
                if(i == 0 || i == rowIndex)
                    list.add(1);
                else{
                    list.add(tmplist.get(i - 1) + tmplist.get(i));
                }
            }
            return list;
        }
    }
}

题目链接：https://leetcode.com/problems/pascals-triangle-ii/