This is a really nice puzzle! I didn't know William Wu wrote a paper about it. I saw it many years ago on William Wu's riddles site[1] (highly recommended). It's one of the most popular problems there. The original thread[2] in the forum has 25 pages, covering lots of approaches. There is also another thread[3] summarizing the discussion.
reminds of the good times i had with wuriddles in high school. definitely wasted many hours talking about the 100 prisoner problem and its variants with others back then. another one i liked was the sink the sub one