Amazing what a break from looking at code can do to help you fix a bug.
Back in 2004, I had been writing articles explaining different sorting algorithms, how they worked, and how to implement them in C (and in most cases, how to implement them more efficiently than the "standard textbook way"). Well, I had gotten distracted around the time I had been working on an article for Quick Sort and never got around to finishing it. I remember having a bug in my QuickSort routine somewhere that I wasn't able to find after a few nights of looking at it and having had more pressing things to attend to, set it aside for later (but not before documenting a few test cases that failed and how they failed).
Well, yesterday, after coming across that code, I opened it up in my trusty Emacs editor and in just a few minutes had a solution... it was basically a simple one-off bug.
Not long after, I got a call from someone at Google who had seen my resume and repeatedly told me they found it "interesting". I have no idea what that means, exactly, but I take it that it's a Good Thing(tm) :)