After Tim Harford Tweeted the link to it, I spent a fair bit of time yesterday wrestling with what XKCD reckon to be

The Hardest Logic Puzzle in the World

Here’s how it runs:

‘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 their own eyes then leave the island, and the rest stay. 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. Everyone on the island knows all the rules in this paragraph.

On this island there are 100 blue-eyed people, 100 brown-eyed people, and the Guru (she happens to have green eyes). So any given blue-eyed person can see 100 people with brown eyes and 99 people with blue eyes (and one with green), but that does not tell him his own eye color; as far as he knows the totals could be 101 brown and 99 blue. Or 100 brown, 99 blue, and he could have red eyes.

The Guru is allowed to speak once (let’s say at noon), on one day in all their endless years on the island. Standing before the islanders, she says the following:

“I can see someone who has blue eyes.”

Who leaves the island, and on what night?’

Now, it’s possible to Google the answer but I thought it would be interesting the explain how I worked it out.Continue reading

Recently I’ve been doing some work with Mudlark on a data vizualisation project. Matt Watkins, their lead technologist, suggested that I might like to subscribe to Flowing Data, a daily newsletter with illustrations of different data viz work.

It’s well worth subscribing to. My favourite recent post had a link to the video below which demonstrates the Bubble Sort algorithm by means of Hungarian Folk Dance.

This was created at Sapientia University in Tirgu Mures (Marosvásárhely), Romania. They have their own YouTube channel as well as Facebook page. And really, what’s not to like?