Amazon (Audible) - 2022 | phone interview | first unique character in a string + zigzag traversal

I recently experienced a 1-hour phone interview with Amazon (Audible) in 2022. The interview consisted of two coding challenges. I found the first question to be quite straightforward and solved it without much difficulty. However, the second question was familiar to me from prior practice, but I unfortunately forgot the specific approach involving a deque during the interview and was unable to provide a correct answer.