Hardest logic puzzle in the world

[Bioture]

The following link:

http://xkcd.com/blue_eyes.html

Claims to be the hardest logic puzzle in the world. I haven't been able to figure it out so far... so test your logic puzzle solving abilities? If you got the answer, please don't ruin it for everyone else... leave an answer that can be highlighted!

[CrvenBan]

There is no need for any big logic, and even tho he said it's not a trick question, this is not a trick:

that midnight after the Guru said: "I can see someone who has blue eyes." everyone goes to the ferry and say "I have blue eyes". Those who are left behind will leave the following midnight saying they have brown eyes... ^-^

[Noah]

If everyone knew that saying the right color would get you off the island, then they would've been gone for a long time ago if they were allowed to guess.

They would just go through the color chart each night, eliminating one color at the time.

[Zeebu]

how about this?

if you see someone without blue eyes, kill them. if you dont die, youve got blue eyes and can leave

edit: unless killing people counts as communication?

[CrvenBan]

easy zeebe! Good solution albeit a bit violent...see there are all kinds of logics... :grin:

[Zeebu]

easy zeebe! Good solution albeit a bit violent...see there are all kinds of logics... :grin:

i do this kinda stuff for fun. i like logic/math puzzles.

[CrvenBan]

oh, I just thought you liked hurting ppl...

[Sufficient]

An interesting problem ... answer is here: http://en.wikipedia.org/wiki/Common_knowledge_(logic)

[Zeebu]

i like mine better, though i guess that one is a more 'logical' solution. mines faster

[Galleleo]

that is actually quite.. logical

[phata$$]

Wow. It took me the longest to just understand the answer.

[Epinephrine]

The key to this is the following sentence:
"Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate."

Read it carefully.

It means that you are allowed to communicate the number of people you see with each eye colour, which means... all you have to do is:

Count how many you see, look at someone else's count, and then deduce what you have.

[Zerzera]

I think the Guru's gone the first night :P

[PjOtTeR]

I made the text white, I hope:

Basicly all blue-eyed ppl leave eventually, since on day one they do not know wether they themselfs have blue eyes, but they know one other person has blue eyes.. They see 99 ppl with blue eyes not knowing wether they themselfs have blue eyes. On day 100, they see that still everyone is there... knowing they themselfs must have blue eyes... this because if they themselfs didn't have blue eyes, all the others would've left on night 99, since then there would've been only 99 people with blue eyes(cause those other guys would've seen 98 guys if he himself didn't have blue eyes.)

So on the night of day 100 after the announcement by the guru all the ppl with blue eyes will leave the Island.

[PjOtTeR]

The key to this is the following sentence:
"Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate."

Read it carefully.

It means that you are allowed to communicate the number of people you see with each eye colour, which means... all you have to do is:

Count how many you see, look at someone else's count, and then deduce what you have.

WTF Epi on drugs?
It's nowhere said you can see the count of other ppl... You can see every other person at all times and you can keep count of the number of people you see with each eye color(except for urself), but you cannot communicate any other way then looking and counting the eyes of others.. So you cannot exchange data...

P.S. I would certainly smack that guru if he could once speak one sentence and said such a stupid one that made all ppl stay longer then needed