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?

class Solution {public:vector<int> getRow(int rowIndex) {vector<int> ivec;if (rowIndex < 0)return ivec;else if (rowIndex == 0) {ivec.push_back(1);return ivec;}else {ivec.push_back(1);for (int i = 1; i <= rowIndex; i++) {for (int j = i -1; j > 0; j--) {ivec[j] += ivec[j - 1];}ivec.push_back(1);}return ivec;}}};