The only mistake the OP made was in acting like they hadn’t seen the question before, but other than that everything was fine. These code screen questions are usually a basic gut check and the real evaluation comes later at the on-site. Honestly the interviewer did a bad job though because the question clearly gives an advantage to someone who has seen it before.

Once I had a candidate struggle with my screening question, flattening an array of nested arrays, and that’s fine because I normally use that as an opportunity to see how they ask questions and work together on finding a solution. But the candidate went silent for about 5 minutes and then came back with a perfect solution, using iterators, which are a pretty obscure JavaScript feature. I later found that exact code block on the MDN site, and I was pretty shocked at how brazen an action it was, because if they had just asked for direction and admitted they were struggling they could have still passed the interview.

There's a famous story about Gauss as a child (age 7 in some accounts) figuring out this trick when a teacher who probably wanted a break had the students add up the numbers from 1 to 100. He saw that you could combine numbers from the ends: 1+100=101, 2+99=101, and there are 50 pairs, so the answer is 5050.

There's also the joke that John von Neumann was given this task and "cheated" by just instantly adding all the numbers in his head the naive way, without having to write anything down.

The traditional story is about calculating the distance a fly (or bird?) travels if it goes back and forth between two trains. https://jcdverha.home.xs4all.nl/scijokes/10.html#Neumann_4

Gauss was cheating since he was born! He fixed math errors in his father accountant stuff at age 3.(according to wikipedia) if thats not an unfair advantage i dont know what is ;)

> The only mistake the OP made was in acting like they hadn’t seen the question before

This. Everyone in the thread is claiming no wrongdoing on the part of the author. If I was in this position, I would excitedly inform the interviewer that I had seen the question before and then quickly write down the answer. But that would look be a lot less impressive than OP’s acting as he pretended to come up with the perfect answer on the fly.

I would have done the same, but I can't blame the author either. He did come up with the solution on his own, after all.

As the adage goes, success is all about luck. Oh, and hard work. And the harder you work, the luckier you get.

"Fortune favors the prepared mind" (Louis Pasteur)

Its just luck. What you worked hard at is also luck.

I tend to think that fate and free will work like electricity and magnetism. I call the combined result 'destiny'.

Really nice way to put it!