（难度Easy） Problem 119. Pascal's Triangle II（杨辉三角II）

Pascal's Triangle II

Easy

## Description

Given a non-negative index _k_ where _k_ ≤ 33, return the _k_ th index row of
the Pascal's triangle.

Note that the row index starts from 0.

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

Example:

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

Could you optimize your algorithm to use only _O_ ( _k_ ) extra space?