I was so pleased when I found a solution to the Car Talk “23 prisoners” puzzler (after four hours of work) that I sent the answer off to David Weinberger (whose blog showed me the puzzler in the first place).

Here’s my answer:

One of the prisoners is chosen to be the Scorekeeper and he gets these special instructions: “The very first time you enter the switch room, turn switch B off. If switch B is already off, flip switch A (just to waste time). Once this first trip is over you are ready to start keeping score in your head. Your score starts at 1. From now on, follow these instructions: If switch B is on, turn it off and add 1 to your score. If switch B is off, turn it on and subtract 1 from your score. Eventually your score will reach 23. When it does, tell the warden that everyone has visited the switch room.” Each of the other 22 prisoners gets these instructions: “You are going to be sending a signal to the Scorekeeper to tell him that you’ve visited the switch room. But you can’t send the signal until you know that the Scorekeeper is listening. When you first enter the switch room, flip switch A