There are twelve wires that run from your cellar to your roof. Unfortunately on their journey they could be randomly mixed up, so you can't tell which cellar wire-end corresponds to which roof wire-end. You have a battery and a light bulb, and you can temporarily twist wires together. You can also travel from the cellar to the roof and back again any number of times. Thus you can construct circuits and test the wires at either end in order to deduce what is going on. But it’s a long way to the roof. So, starting at the bottom, what is the minimum number of journeys you have to make, in order to work out exactly which wire-end in the cellar corresponds with which wire-end on the roof?

(In reply to Saving one trip by Charlie)

While that modification will work for identifying each wire in the 4-wire group, it still leaves a pair in each of the 3-wire groups unmatched within each pair, so you still need to be at each location twice.

Posted by Charlie on 2004-06-30 15:43:21