Leave one switch on, leave one switch off, and the other switch you turn on and off as fast as you can, for hours. Get in the room. The turned on lightbulb is the one with the turned on switch. Take that lamp off, and plug one of the other two lightbulbs (both will be turned off). If that one doesn't work, that means it's the lightbulb you were turning on and off (until the ligthbulb got burned off), and the other one belongs to the switch you turned off. Got it?