Pascal's Triangle II

题目：

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?

 

Code：

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=1;i<=rowIndex;i++)

        {

            

            for (int j=result.size()-2;j>=0;j--)

            {

                result.set(j+1,result.get(j)+result.get(j+1)); //****Good Idea!!!

            }

            result.add(1); 



        }

        

        return result;

        

    }

  

}