编程开发Pascal's Triangle II解析

编程开发Pascal's Triangle II解析。Given an indexk, return thekthrow of the Pascal's triangle.

For example, givenk= 3,
Return[1,3,3,1].

Note:
Could you optimize your algorithm to use onlyO(k) extra space?

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