leetcode 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?

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 = 15
Number = 22
Number = 25
Number = 30
Number = 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;
    }
}