Brain teaser interview questions

Here's a quick list of common brain teaser questions that come up on technical interviews.  They're fun exercises, and usually that have on AHA moment that gives away the whole trick.  The real question is how can you train your brain to be flexible enough to recognize those tricks.  

Three light bulbs question

A room with three light bulbs and 3 switches outside of it.  You can only enter the room once.  How do you determine which switch controls which bulb.  

Thought process: if you flip one or two light switches then enter, you'll only be able to tell one blub for sure.  The solution is to use the heat of the bulbs to tell which one you just turned off.  The rest is easy. The problem for you, is how do you avoid this thought process...

Hmm, I can do 2, I can do one, I can do all of them.  Now I'm stuck, I must be missing something.  I'll grind away at this impossible scenario.  

Tips

• Be careful with how you first visualize the scenario.  I pictured a room where I couldn't touch the bulbs, and it stayed that way in my head.  Maybe if I revisualsed the scenario I was in.
• I find it useful to think of these problems as if I'm standing right there.  If somebody gave me this scenario in the real world, I think I could have figured it out.  Question is how do you get your brain into the real world and not this conceptual one in your head.