Prisoner puzzle.
Thursday morning flight back home from Maryland and New Jersey. Puzzle time!!!
Since last week I was pilloried for lowering my standards of puzzle (once again, I am amazed that people think I have standards), I picked a slightly harder one this week. I heard a variation of this in Car Talk last week as I was taking Tasha somewhere.
If you know this, you will get it immediately. If you had heard this before, it is fun trying to remember the answer. If you have never heard it before, it would be interesting to solve it. Let me know thru FB message if you would like some hints.
As always, do not write on comments section if you have figured it out. This is to give others a chance to solve it. Send me a FB message.
There is a slightly easier version and a slightly tougher version of this puzzle. The puzzle goes roughly like this.
There is a prison with 15 prisoners for life in individual cells with no ability to communicate with each other whatsoever. One day, the warden took all of them out and gave them a chance to go out free. However, there was a catch.
He showed them an isolated room from outside in a separate part of the jail and told them that there were two switches inside. One on the left and the other on the right. The switches were connected to absolutely nothing. They could only be flipped to the on or off position.
The warden, starting the next day, was randomly going to pick a prisoner – at random times (could be few a day or could be none some day) – and take him inside the room. While inside, the prisoner would have to flip any one switch once. (If it is on, he flips it off and vice versa). However, he had to flip one (and only one) switch. He could choose which one to flip, of course.
Slightly easier version: The warden told them that both the switches were initially in off position.
Slightly more difficult version: The warden told them that nobody – including himself – knew what the starting positions of the switches were.
And then the warden said – “I need somebody among you – I don’t care who – some day – I don’t care when – to come and tell me that you are confident that all the prisoners have visited the room at least once. If that person is right, all of you go scott free. If not, all of you will be put to death.”
He gave them sometime to get together that day to devise a strategy to see if they could come up with a foolproof plan to get out.
Can you suggest a strategy (for both the easier and more difficult case)?
Remember, they don’t need to tell immediately after all of them have visited once. They just need to be absolutely sure that each one of them has visited the room at least once.
