注意k从0开始算。
附上代码：

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.
        rowIndex++;
        vector<int> ans(rowIndex);
        if(rowIndex == 1)
        {
            ans[0] = 1;
        }
        else
            if(rowIndex == 2)
            {
                ans[0] = 1;
                ans[1] = 1;
            }
            else
            {
                ans[0] = 1;
                ans[1] = 2;
                ans[2] = 1;
                for(int i = 4;i <= rowIndex;i++)
                {
                    ans[0] = 1;
                    ans[i-1] = 1;
                    for(int j = i-2;j >= 1;j--)
                    {
                        ans[j] = ans[j-1] + ans[j];
                    }
                }
            }
        return ans;
    }
};