Wouldn't that be a "mirror" operation, while inversion would be (I dunno) swapping the direction of the edges?
I went out of my way to avoid homebrew (still do) when I worked at google because it would reliably fail to complete some key operations in a dag, hence the interest in ensuring developers know how to do CS things.
Yeah it's not clear what he was asked. Swapping the direction of every edge of a binary tree would result in a DAG that is likely no longer a binary tree though.
"Mirror" is what this question is generally understood to be asking. I don't think swapping the direction of the edges produces a tree in general although it would produce a DAG. I think "invert" could mean "mirror" or turn upside-down depending on the context.
