[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) {
    // IMPORTANT: Please reset any member data you declared, as
    // the same Solution instance will be reused for each test case.
    vector<int> ans;
    ans.push_back(1);
    for(int i = 1;i <= rowIndex;i++)
    {
        for(int j = i; j > 0;j--)
        {
            if(j == i) ans.push_back(1);
            else
                ans[j] = ans[j - 1] + ans[j];
        }
    }
    return ans;
    }
};