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?

1,因为题目中要去用o（k），所以就用本身的arraylist；采用覆盖的方法

2， 注意arraylist的add的用法，

arrlist.add(15);    arrlist.add(22);    arrlist.add(30);    arrlist.add(40);    // adding element 25 at third position    arrlist.add(2,25);
结果如下：

Number = 15Number = 22Number = 25Number = 30Number = 40；

3，arraylist的set则会取代原来index的值！！！

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

leetcode Pascal's Triangle II