Given an integer `rowIndex`, return the `rowIndexth` (0-indexed) row of the Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

Example 1:

    Input: rowIndex = 3
    Output: [1,3,3,1]

Example 2:

    Input: rowIndex = 0
    Output: [1]

Example 3:

    Input: rowIndex = 1
    Output: [1,1]

Constraints:

- `0 <= rowIndex <= 33`

Follow up: Could you optimize your algorithm to use only `O(rowIndex)` extra space?