This Devilishly Hard Logic Puzzle Will Save Your Life

gizmodo.com

2 points·ourmandave··3 comments

There is a certain era of history, for which an "all-powerful mad villain...who is always true to his given word" sounds at least faithful to the literature of the time period.

The puzzle's description seems odd -

> After everyone has had time to observe everyone else’s numbers, your captor counts down and you all must shout a number at the same time. If at least one person guesses the correct number on their forehead, then you all go free.

Either you are shouting out your guess (of the number on your forehead), or you are passing information to other participants in advance of the guessing round. If the latter, solutions seem trivial. If the former...you're guessing at a number from 0 to n-1, with no prior information.

Or maybe I'm just unfamiliar with the unwritten assumptions of such puzzles.

[rot 13, I don't know if HN has spoiler tags]

Nffvta n qvssrerag inyhr zbq A rnpu naq rnpu thrff gur ahzore gung jbhyq znxr gur gbgny gung inyhr vs vg jnf ba lbhe urnq?

[I don't think HN does...but after 18 hours here, the puzzle has only 1 upvote and 2 responses here.]

I assumed the sequence is (in effect):

- Quietly look at the numbers on everyone else

- Quietly decide what number to shout

- All shout when a signal is given

- Somehow hear and understand what everyone shouted simultaneously

- Quietly decide on your guess (at the number on your own forehead is)

- All reveal their guesses when a signal is given

If that's correct - then everyone can just shout the lowest number they see on someone else, then give the lowest number they heard shouted as their guess. That number is on someone's forehead, and one correct guess lets everyone go free.

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