# Interview Questions and Answers: Think you can do better?

2009-06-02 08:11:08

As most people reading this blog know, we recently launched a new feature that allows anyone to post reviews of interviews they’ve had with various companies, including the difficulty level and actual questions asked. What you might not know, however, is that anyone in the Glassdoor community can answer these questions as well. And for many, we’ve received some great answers.

While for the people actually asked the questions, it’s likely too late to get this feedback, but for anyone interviewing at the same company, or even for the same position, the power of the community can be very powerful in suggesting different ways of thinking about these types of questions. It can also spur  a good debate and raises the question- think you could answer it better?

We’ve pulled two key examples of this below, along with some of the suggested answers the community provided. Think you could suggest a better response?:

Question: You have two light bulbs and a 100-story building. You want to find the floor at which the bulbs will break when dropped. Find the floor using the least number of drops. – Software Engineer, Facebook

Start moving up in increments of 10 floors and dropping the bulb until it breaks (i.e.: drop from floor 10, if it doesn’t break, drop from floor 20, etc.). Once the bulb breaks, move down to the floor above the last floor it broke on and start moving up floors in increments of one until the second bulb breaks. This results in a worst case scenario of 19 drops.- by Interview Candidate

If you do a binary search, what happens if it breaks at floors 50 and 25?- Anonymous

Do you know what a binary search is? You drop it from floor 12 next. If it breaks, you know it breaks between floors 12 and 1, inclusive. If it doesn’t, you know it breaks between floors 13 and 25, inclusive. The main principle of binary search is that with each step you reduce your search space in half. Now your search space consists of only 12 floors. Wow, I want to get asked such a question in an interview!- Anonymous

19 drops is not the best worst case scenario… imagine trying floor 16, if it breaks, you try 1 – 15 and thats 16 tries. If it doesn’t break, then try floor 31 and if it breaks, then try 17 – 30 (so 16 tries, including the try on floor 16). And on and on (45, 58, 70, 81, 91, 100). If you reach 91, you’ll have tried 7 floors so far and if it doesn’t break, then there’s 9 more tries to get to 100 (thus 16 in the worst case) – Anonymous

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