Is it possible that $f(n) \not\in O(g(n))$ and $g(n) \not\in O(f(n))$

Question

As the question stated, can I find any two functions $f(n)$ and $g(n)$ such that they satisfy:

1. $f(n) \not\in O(g(n))$
2. $g(n) \not\in O(f(n))$

Answer 1

$$f(n) = \begin{cases} 0 & \text{ if } n \text{ is odd}\\ n & \text{ otherwise} \end{cases}$$

$$g(n) = \begin{cases} 0 & \text{ if } n \text{ is even}\\ n & \text{ otherwise} \end{cases}$$