Hired by Google?

March 5th, 2006

I had a phone interview with Google today. I took notes; some of the questions they asked were interesting. We were allowed to ask questions. The interviewer didn’t ask many questions in response to my answers, except to occasionally say “interesting”. There’s almost certainly more than one answer to each of these, and a few are probably wrong answers or could be improved in some way; I only include my answers for comparison. Any intermediate questions that I asked for clarification or otherwise have been omitted.

Without further ado, a few of the more interesting ones:

Q: “You are shrunk to the height of a nickel and your mass is proportionally reduced so as to maintain your original density. You are then thrown into an empty glass blender. The blades will start moving in 60 seconds. What do you do?”

(my answer): Take off all my clothes, wedge them between the blades and the floor to prevent it from turning. Back up against the edge of the blender until the electric motor overheats and burns out. Using the notches etched in the side for measuring, climb out. If there are no such notches or they’re too far apart, retrieve clothes and make a rope to hurl myself out.

My answer: go down to the base of the blades and duck. Mixer blades in blenders normally have a gap underneath them, and in some blenders, the blades are curved. You could survive for a long time crouched down there. With your fingers in your ears.

Q: “How would you find out if a machine’s stack grows up or down in memory?”

(my answer): Instantiate a local variable. Call another function with a local. Look at the address of that function and then compare. If the function’s local is higher, the stack grows away from address location 0; if the function’s local is lower, the stack grows towards address location 0. (If they’re the same, you did something wrong!)

My answer: The last time I programmed in Assembler was 1979.

Q: “Explain a database in three sentences to your eight-year-old nephew.”

(my answer): A database is a way of organizing information. It’s like a genie who knows where every toy in your room is. Instead of hunting for certain toys yourself and searching the whole room, you can ask the genie to find all your toy soldiers, or only X-Men action figures, or only race cars — anything you want.

My answer: A database is like a pack of Top Trumps in its plastic box. Instead of Gumball Cars, Fast Boats or other Top Trumps stuff, you can make up your own deck. You can then do all kinds of Top Trump like things, comparing cards and stuff like that.

Q: “How many gas stations would you say there are in the United States?”

(my answer): A business doesn’t stick around for long unless it makes a profit. Let’s assume that all gas stations in the US are making at least some profit over the long run. Assume that the number of people who own more than one car is negligibly small relative to the total American population. Figure that 20% of people are too young to drive a car, another 10% can’t drive because of disability or old age, 5% of people use public transportation or carpool, another 5% choose not to drive, and another 5% of the cars are inventory sitting in lots or warehouses that a dealership owns but which no one drives.

There’s about 280 million people in the US; subtracting 50%, that means there’s about 140 million automobiles and 140 million drivers for them. The busiest city or interstate gas stations probably get a customer pulling in about twice a minute, or about 120 customers per hour; a slower gas station out in an agrarian area probably sees a customer once every 10 or 15 minutes, or about 4 customers per hour. Let’s take a weighted average and suppose there’s about one customer every 90 seconds, or about 40 customers an hour. Figuring a fourteen-hour business day (staying open from 7 AM to 9 PM), that’s about 560 customers a day.

If the average gas station services 560 customers a day, then there are 250,000 gas stations in the US. This number slightly overstates the true number of gas stations because some people are serviced by more than one gas station. [Actual number in 2003, according to the Journal of Petroleum Marketing: 237,284, an error of about 5%.]

My answer: There are too many gas stations and too many cars in the United States of America.


2 Responses to “Hired by Google?”

  1. captain davros Says:

    What a horrible, horrible set of questions! Particularly the one about the blender.

  2. irdial Says:

    Why? They use these questions to see what sort of character you have, to see if you are a defeatist or not, to see if you are a lateral thinker.

    Companies like Google do not want sour, po faced people to work for them, they want the brightest (in every sense of the word) people there, people with the spark of life, enthusiasm, curiosity and an ability to think obliquely.

    Thats why they ask questions like the blender one; it tests wether or not you are a quitter, and wether or not you have a vivid imagination. If you can see yourself in that totally bizarre context, and think of a way out, then you are more likely to be able to figure out how to search a database of a biilon pages across a distributed network, instead of saying “I would let the blades chop me up” as some people have answered, implying that you would just throw your hands up at a seemingly intractable problem and say “lets give up”.

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