Friday, September 19, 2008

Ten Greedy Pirates

I've just been informed that today is Talk Like a Pirate Day! You will not actually see me talking like a pirate, but I've got a pirate-themed puzzle classic.

Ten greedy pirates need to split 100 gold coins. These being pirates, they do not split it fairly. The oldest pirate decides exactly how to split the gold. But after he's decided, if more than half of the pirates (including the oldest one) are unhappy with their share, a mutiny will occur. They'll kill the oldest pirate, and start the procedure over.

All pirates have the following priorities in this order:
1. Every pirate wants to stay alive.
2. If they will stay alive either way, the pirates would like as much gold as possible.
3. The pirates are not friendly with each other. All other things being equal, the pirates would prefer mutiny.

The pirates' behaviors are entirely predictable; there are no psychological games being played here. How should the oldest pirate split the gold?

Hint! Try solving a simpler case (ie less pirates) first.

For an extra challenge, replace the bold "more than half" with "at least half". For this challenge problem, I have to add an extra priority. If it doesn't matter to himself, the oldest pirate prefers to give gold to the youngest pirates possible. Have fun with that one.

Spoiler! Solutions have been posted