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;
        
    }
  
}