[leetcode]Pascal's Triangle II

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?

算法：

思路1：

跟[leetcode]Pascal's Triangle 几乎一样，用2k个空间就可以搞定

思路2：

对空间进行优化，用k个空间搞定

 public List<Integer> getRow(int rowIndex) {
        List<Integer> result = new ArrayList<Integer>();
        if(rowIndex < 0) return result;
        result.add(1);
        for(int i = 1 ; i <= rowIndex;i++){
            result = getNextRow(result);
        }
        return result;
    }
    private List<Integer> getNextRow(List<Integer> list){
        int tem = 1;
        for(int i = 1; i < list.size(); i++){
            int a = list.get(i);
            list.set(i, list.get(i) + tem);
            tem = a;
        }
        list.add(1);
        return list;
    }