You are working in a building and have a problem. On the top floor are three standing lights. On the ground floor are three switches, which control the lights, presently all in the "off position. You don't know which switch controls which light, except that there is a one-to-one correspondence. You're down on the ground floor and want to label the switches. But you want
to do it in as few trips up stairs as possible.
The room the lights are in can only be seen from the top floor (it has no windows and its at the end of a long corridor.) There's no one around to help. You must do it alone.
What is the fewest trips you can make to determine which switch turns on which light? You may assume that the bulbs have just been replaced, all the wiring is good, etc.