I work and interview for one of the FAANG's. I had a candidate tell me just the other day: "Oh, I've done this in another form." We went on, talked about some details that are not a part of the core algorithm but that I think are interesting to suss out things like: "Do they understand concurrency", "Do they understand good API design", etc and then we moved on.
As I was doing the writeup, I scored the person high on a measure that I rarely get a read from in technical interviews. I guess my point: I don't know if it's cheating and in no way shape or form feel judgy towards people who do what the author did. But when I've encountered people disclosing this, I have noted that.