If they knew it from working at Meta, it wouldn't be O(n), it would be O(1).
I agree that there will be cases where you implement tricks that others have had before you, without knowing. A few years ago, I had a delightful idea, experimented and wrote it up. One commenter directed me to a post that described it as "folk knowledge". There will be other cases where you encountered an idea before, but didn't remember it.
Still, crediting what you can easily know you cited is good. Even aside from credit, comparisons to existing systems are part of how we understand what a system does.
I agree that there will be cases where you implement tricks that others have had before you, without knowing. A few years ago, I had a delightful idea, experimented and wrote it up. One commenter directed me to a post that described it as "folk knowledge". There will be other cases where you encountered an idea before, but didn't remember it.
Still, crediting what you can easily know you cited is good. Even aside from credit, comparisons to existing systems are part of how we understand what a system does.