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?

vector<int> getRow(int rowIndex) {
        vector<int> result(1,1);
        if(rowIndex==0)return result;
        result.push_back(1);
        if(rowIndex==1)return result;
        int i=2;
        while(i!=rowIndex+1)
        {
            vector<int> tmp(result);
            for(int j=1;j<i;j++)
            {
                result[j]=tmp[j-1]+tmp[j];
            }
            result.push_back(1);
            i++;
        }
        return result;
    }