[derefr]

The important part of the "realistic" process is the part where you go from "the crawler's indexing is too slow" to "it might be because it allocates a lot of little bits of memory; it needs to first generate a BST of outbound link weights, and then functionally invert that into a second graph with a bunch of inbound link weights, and then inject all that into the PageRank matrix. You could probably save some time (though at the cost of memory-safety) by inverting the first BST in-place."

Once you get to that point, though, if they asked me "and how would you invert the tree in-place?" I'd answer "well, first I'd make sure we aren't just using a tree structure that already knows how to invert itself, or could easily be extended to know how. Then, assuming that didn't pan out, I'd google 'in-place invert binary tree' and read three or four solutions that already exist to burn the semantic structure of what I'm about to write into my head so that I don't subtly screw it up and have to fiddle with it for the next hour when I could be coding something else. Then I code it."

And that should be enough.