Logic puzzle

[stevie_goblin]

Courtesy of XKCD - A logic puzzle

Blue eyes

A group of people with assorted eye colors live on an island. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. Any islanders who have figured out the color of

Comments

[yorkshire_spam]

Hmmmm, I hope the answer is in the question and not something like "everyone knows that the guru can see into the future/past" or somethings daft like that.

[yorkshire_spam]

That night the Guru and the one remaining person, who has blue eyes leaves. All the rest left before then when the guru told them what their eye colour was.
Or is this the first and ONLY time the Guru has spoken?

[stevie_goblin]

The answer is in the question (after some very long and recursive inductive logic). The writer has tried to be very clear about which information to include to make it unambiguous.
The Guru speaks only once (and this is it).

You are working along the right lines with starting out with the hypothetical (and trivial) case of only 1 person with blue eyes.

When I looked at it, I got the right answer but through a slightly different route (that I wasn't fully happy with before I checked with the answer)

[yorkshire_spam]

The "git" in me says that the answer is either everyone OR everyone except the Guru, on the grounds that if everyone is a perfect logician and one fo them can work it out, then they can all work it out (with the possible exception of the Guru) But that's hardly a satisfactory answer to the question of how THEY work it out.

[yorkshire_spam]

on the first night, nobody leaves.....
nor on the second, third, forth or fifth......
On the 100th night the people with blue eyes know that they have blue eyes?