I also put it off to the last minute. I had a pernicious bug in my coalescing code that was hard to debug. After one failed rewrite and only a few hours left, I resorted to taking the book's array version and optimizing it for utilization. My throughput was shit but I was able squeeze past their minimum score and squeak a C. My semester, the grading was pretty tough, only 6 or so people over 90. In other semesters, I know at least that many get 100.