Interviewing @ eBay Part II - Software Engineering Interview

I am writing this hoping that candidate interviewing with eBay find this BEFORE their interview (if you did please let me or your interviewer know), but if you are not interviewing with eBay you may still find it useful.

Be prepared for the following category of questions:

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Explain a project or a problem you worked on

Be prepared to talk in some detail about an interesting, or challenging, important and otherwise mentionable project in your career. Even if you are fresh out of school, there must have been some special class or final project. You should clearly talk about the problem, and describe how you arrived at the solution, your implementation and result …what you learned, where/if you failed, how you fixed it etc. The way you communicate, what you choose to communicate is almost as important as what the project actually was. So be direct, clear and to the point. Be prepared to defend your choices. Do not play it “safe” by saying “..well this was not my decision”, or “Oh..I didn’t like this approach, my boss asked me to do this” etc.

-        Data Structure and Algorithm

Brush up on basic computer science, know data structure. You will be asked a few questions about graphs, hash maps, trees and complexity. Familiarize yourself with how graphs are represented in memory and in persistent storage, how maps and hash maps are implemented, how to traverse trees – basic stuff. Please DO NOT trivialize the questions by saying “oh, there is APIs for this in Java, I never need this in real life”. This, in addition to demonstrating bad judgment and wrong situation assessment, does not get you off the hook!  You should demonstrate that you are an engineer not a technician.  

-        Programming Language

Well, you are applying for a software engineering position, so you must know one or more modern programming languages very well (at least much better than I do) – eBay is a Java shop, so knowing Java really helps.  You should be proficient in basics (variables storage classes, access modifiers, memory management, basic object orientation) as well as advanced features such as multi-threading and concurrency, generics, network programming etc.

You will be asked to write code or code snippets on the white board. I am amazed how many people are surprised when they are asked, for example, to write a simple singleton class on the board. It shows how comfortable you are with coding, syntax does not matter at all, so don’t be shy.

-        Basic Modeling  

You are expected to know how to model basic stuff for example a simple book store, or an email client. You should be able to break it up to basic entities and their relationships. Sometimes I ask candidates to model “eBay Marketplace”, do not be overwhelmed, you are not expected to model entire eBay, do as much as you can and do “out loud” thinking. You approach is as important as final design.

-        Problem Solving

We are engineers, we solve problems. So you have to be able to frame and analyze problems, recognize tradeoffs in different solution and pick one. So prepared for questions such as “Estimate eBay marketplaces revenue” or “What happens if minimum wage is raised to $100/hr” or “Is hybrid cars more economical or full electric cars?”, “how do you prevent a corrupt DBA from stealing eBay data”, it goes without saying that the actual answer is not really as important as how you think thru the problem.

-        “Soft Stuff” - General attitude, fit, personal qualities

These may or may not be actual questions, but I’d like to see evidence of several personal qualities for example that you have passion, you care about the stuff that you are tenacious and don't give up easily, that you recognize your mistake you learn from it, that you know what a reasonable compromise is and are willing to reach one, that you can deal with conflict in a constructive way – and for more senior candidate - that you can influence people around you especially on why and what and not simply on how. Also I ask our candidates to tell me what they think a few major trends in technology are and why

-        And finally, please know the company

Last but not least, please familiarize yourself with eBay if you are not familiar with it, nothing gets your rejected faster than saying “eBay? Who uses eBay? I am really not familiar with it” – OK, this is an extreme case but hey it is real. It is  

Of course if you are being interviewed for a particular area, e.g. security, Hadoop or Eclipse tools development, you should expect a few questions in addition to the above in each particular areas, for example in security, you should be very comfortable with authentication protocols and practices (zero proof, Diffie-Hellman algorithm, Kerberos etc.) authorization techniques, RBAC, ABAC, XACML , basic cryptography etc.

You may ask, how about other stuff, such as JavaScript, CSS, SQL, Unit Test etc. etc. Yes there are a lot of technologies and techniques used in building large internet apps, but my beleife is that if you know the basics and possess the basic qualities, even if you don’t know the rest, you will be a successful productive engineer.

Interviewing @ eBay, Part I - The basics

When someone interviews with eBay, s/he is given an interview schedule with the name and title of all interviewers, the natural expectation (at least mine) is that s/he searches for the name of all those people as part of the pre-interview preparation. I view this as minimum due diligence that a candidate should do 11 years into the 21^st century. So I hope whoever interview with me at eBay finds and reads this post (if you do, please let me know)

Now that you found this, I will give you a leg up over other candidates:  in the series of four posts, I tell you what questions I would be asking in my interviews for four positions:

• -        Software engineer
• -        Product Managers
• -        Software Architects
• -        Engineering Managers (Sr. Managers, Director, Sr. Director and VPs)

Before we start with specific position, let me first cover the common questions and aspects for all interviews.

I look for the following “necessary” – but not sufficient - qualities that make a candidate productive. In a nutshell, person should be smart, know his field, willing to work hard, willing to compromise and get things done and get along with people under a range of circumstances.

Smart: I am not talking about genius, or someone that can solve puzzles in 10 seconds, but some one that is generally sharp, can think on his/her feet and is solve problems. One of the clearest indication of it is whether someone listens to question, asks follow up questions to clarify what is being asked and then clearly and directly answers that question and then stop. No rambling, no answering other questions and no circular, perpendicular or random answers!

Knowledgeable: Candidate must have proficient level of knowledge in his/her domain, this is separate from being smart, each field requires certain level of experience and formal education – I expand on this with specific question in each of the fields above.

Work ethics: Regardless of how smart and knowledgeable one may be, s/he has to be focused and will to work hard. Real engineering tasks are 10-20% about great ideas, and 80% about grunt work, boring details, dealing with plumbing,  debug, re-build, fine tune etc. If you are not willing to do that, you won’t be successful.

Pragmatic: You must be willing to compromise, change course, give up credit, change your familiar and favorite terminology etc. to get things done. All the smarts, knowledge, hard work often is wasted if you cannot get it done and out at the end. I ask what you are willing and what you are not willing to compromise on for a given project and why, what you would do if you feel a wrong decision was made…

Culture fit: The last of the “necessary qualities” is the ability to get along with others under all sorts of circumstances: uncertain and insufficient data, deadline pressures, failures, inter personal and inter group rivalries … under all those conditions, you should be able to maintain your relationships and get along with others. One of the greatest indicators of whether someone can do it by the way, is sense of humor.

Next post: my list of questions for Software Engineering positions.

On Bullshit...

As some one who

1- Deals with his fair share of a BS
2- Needs to have definitions for everything

I have been missing a formal definition for BS. Courtesy philosopher Harry G. Frankfurt book "On BullShit"  - via Ian Bogost post - that issue has been remedied now.

"It is impossible for someone to lie unless he thinks he knows the truth. Producing bullshit requires no such conviction. A person who lies is thereby responding to the truth, and he is to that extent respectful of it. When an honest man speaks, he says only what he believes to be true; and for the liar, it is correspondingly indispensable that he considers his statements to be false. For the bullshitter, however, all these bets are off: he is neither on the side of the true nor on the side of the false. His eye is not on the facts at all, as the eyes of the honest man and of the liar are, except insofar as they may be pertinent to his interest in getting away with what he says. He does not care whether the things he says describe reality correctly. He just picks them out, or makes them up, to suit his purpose."


WOW ..didn't know there were so much academic work done on BS.

Social Norms, Market Norms and IDPs

Last week LinkedIn caused a backlash and lost a lot of good will – including mine – by opting everyone into their social advertising program. Before that there was (and still is) a LOT of discussion – and disagreement – about Google+ strict real name policy and the words facebook and privacy can almost be used as antonyms…

But why users react so strongly to use of their identity, relationship and data by these networks, after all most people, I presume, understand that companies like Google, FB, LinkedIn etc. are for profit firms with the goal to make money, and that is a the core of most of their policies (and not that anything is wrong with that!).

As someone once said “if you are not paying them, you are not their customer, you are their product”, and, as harsh as it sounds, they do (and have to) sell their product one way or another.

I am not claiming that one unified theory explains the users’ strong reactions to them - and possible solution - but Dan Airely in “Predictable irrationality” may come close. If you have not read “Predictable irrationality” you should. It is an easy read and a very enlightening book – not to mention entertaining – by behavioral economist Dan Airely.

Among many interesting observations he makes is the notion of “Market and Social Norms”. It is basically a very simple and common sense notion: All of us live in two worlds simultaneously, a social world where exchanges of good and services are regulated by social norms, the need for being part of a community and a delayed- reciprocity, and a market world where exchange of goods and services are regulated by a cold, sharp edge rules of the market, prices, interest rates, cost and benefits. Life is good as long as these world are kept separated (as George Costonza famously pronounced) – but when you mix the two the real trouble starts and “it blows up”.

Airely gives a few examples: You go to your mother-in-law for thanksgiving and offer to pay her a large sum for the sumptuous spread she put on the table for you … and next year you’d be sitting in front your TV with a frozen dinner. Or more vividly, the example of a guy who takes out a girl to three or four expensive dates and finally brings up the subject of money and how much the romance is costing him! …and of course suffers the dire consequences. Next time he will sure remember Woody Allen’s word of wisdom: “The most expensive sex is a free one”.

The “Social Networking” sites and identity seems to be a classic example of crossing social and market norms. The use of social networking sites is free and there is no other signal that the relationship between user and network operator is a market or commercial relationship. Users may feel/perceive that they are dealing with a “host” one that allows them to interact with their friends, family and catch up on “social” stuff …you know, everyday life that is so outside the “market norms”. I don’t have data but I feel users do understand that these sites have to make money, and are OK with some ad poping up from time to time or being displayed alongside their content, but I doubt that most people understand how those ads relates to their data (posts, searches, conversations etc.) . Every now and then someone (say WSJ or some tech blog) reminds them of how their data is being shared with others – or why the need to “report” accurate names – and that is the moment where “worlds collide”.

Maybe (and only maybe), if an identity provider (or social network) actually started an informed conversation with its users about the data sharing and gave them meaningful control, can it bring the relationship to the “market world”. In that world users are not the network “product”, but informed partners. For example, if an identity provider (or network operator) makes it clear to me that they can get me a good deal on a camera lens with free shipping if I give them my shipping address and the consent for them to obtain the shipping history to that address from a few large merchants, then I may be happy to share my address – that is firmly a relationship in market domain – and I am happy, but when I start to see ads from drunk-driving lawyers in Denver area b/c I searched for “maximum legal blood alcohol level”  - I was taking an online traffic school exam to clear a ticket – while attending a conference in Denver area, that is crossing  the line, and that is when I might have come close to understanding how that girl felt on the fourth date in Dan Airely’s example!