Sunday, October 14, 2012

All those interview questions and brainteasers...

It has been a while since this blog was created. It is intended to be a handy way to look up questions and brainteasers for interview preparation, although from time to time other relevant and interesting stuffs are also discussed.

I have recently once again been looking at a lot of the popular quant interview questions, and an idea comes to mind: perhaps it is worthwhile to re-do some posts in a more systemic manner? Instead of listing the questions and answers out, maybe a discussion of the brainteasers according to their solution technique would bring about more benefits?

It is with this spirit that I embark on this little project. In the following number of posts I would try to group different interview questions into categories and discuss them in more detail, especially how one should approach and attack them. You would find that all previous interview questions/brainteasers posts are now linked here; those posts would remain where they are, so you can think of this post as an overview or introduction.

Where to find more interview questions and brainteasers?
There are two popular printed books that are used extensively in interviews:
A Practical Guide To Quantitative Finance Interviews by Zhou, and
Heard on The Street: Quantitative Questions from Wall Street Job Interviews by Crack
Also, Frequently Asked Questions in Quantitative Finance by Wilmott has a relatively short section on brainteasers, although it is a compilation of materials available on his awesome website (see below). Quant Job Interview Questions And Answers by Joshi et al seems to be a good source too, though I have not read it myself.

Apart from printed books, there is an abundance of resource on the internet. The brainteaser section on the forum of Wilmott.com often has some original questions. Sites such as Braingle and Brainden are dedicated to brainteasers, although those might not be the ones that usually show up during interviews. For those looking for real challenges, wu :: forums should be able to keep you busy.

Finally, if you search the site Glassdoor for a particular company, there will be a bunch of questions that are submitted by those who have interviewed with the firm, with attempts to answer the questions (the quality of which can vary). If you can read Chinese, mitbbs.com has more questions that have actually been asked by interviewers (usually banks).

What should I expect?
Some brainteasers don't really require lengthy calculation. It takes a very specific 'Eureka' moment to be answered. It's fair to say that you won't know the answer if you haven't seen it before. And in case you wonder, yes, such questions do show up at interviews.

Otherwise, the majority of the questions does require calculation. When you are practising, don't just memorize the answer (that's obvious). Think about 1) why the answer is what it is; 2) whether there are alternative, shorter and sweeter ways to solve it; and 3) if the question could have been altered or extended. One thing that I find especially useful is to verify the answers using simulations. That not only assures you of correctness, but also gives you some intuition, as well as a handy way to play with different parameters and assumptinos.

So, here we go:

The series
Those damn coins... 
Those damn coins... (Part II) 
Those damn coins... (Part III)
More Coin Problems
Those damn dice...  
Those damn dice... (Part II) 
Those damn cards... 

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