You have N coins, 2 of which are radioactive. You have a radioactivity
detector which can test any subset of the coins at a time, and return the
number of radioactive coins in the group (i.e. it returns 0, 1 or 2). You have to find the radioactive coins, using not more than 10 tests. What is the largest N for which this is possible?
(In reply to
re(2): New high  Marvelous by Joel)
some code tweaks and a better machine got me to:
8 : 65
(i.e. 66 coins requires 9 tests and 65 can be done in 8)
which is changing my projections slightly to mid 190s, possibly low 190s
Since that is about 3 times where I've gotten so far and I think my code is using exponentially more time as it progresses, I don't have much hope for actually solving the problem directly via this code. Still, it is gratifying to get a little closer. I've got a few more algorithmic improvements to make.

Posted by Joel
on 20061020 17:48:05 