I was asked 2 questions:

1. https://leetcode.com/problems/copy-list-with-random-pointer/
2. A variation of https://leetcode.com/problems/add-strings/
   Where input strings can contain decimals (and ofcourse large large numbers that any string-to-int build-in operations cannot be used directly on the given number).

Both of these questions weren't DS intensive.
Both of these questions should come under "Medium" level difficulty in Leetcode.

Interviewer was easy going, not paying too much attention on smaller edge cases.
Coding was on C++, and showing-off modern C++ skills were taken positively.

My solutions:

1. copy-list-with-random-pointer:

2. Add strings (assumption string lengths are of equal size)

Update:
I was invited for the onsite rounds. You can read my post here: Facebook Onsite Seattle Feb 2020