a companion discussion area for blog.codinghorror.com

The Hardest Interview Puzzle Question Ever


Yep, ms doesn’t give these puzzles at interviews anymore. But! Puzzle hunts are regularly held. See the old one here: http://puzzlehunt.isetv.com/.



re manhole covers are cast casting a circular shape is not has hard as casting say a square one.

and 99% of BT’s Man hole covers arent round


Yes, I know the really good reason manhole covers are round. It’s because that’s the only shape which, no matter how the cover is turned or swiveled, prevents the cover from accidentally falling down the hole.


I have sat in on many interviews, and given my fair number, and it is a bitch to find out much about people. I tried a technical test, with a list of questions (like What id the difference between for, do…while and while…do), but this showed mostly that people studies, not that they did.

The last time I interviewed C++ programmers, I asked them to (gasp) write code and (bigger gasp) design a system. I was amazed how hard people crashed. You may not be able to BS your way through a technical presentation, but you definitely can’t BS your way through writing real code!

There were only three questions, which required about half a page of answer each. One required real code, one required some sort of design and one required discussion. I am happy with the ONE person out of 5 that actually could give me answers, and he has turned out to be pretty much what we expected from the interview.

(Note. One interviewee, who was applying for a C++ job, asked if he could write the simple program in Pearl…)


Hey Jeff,

A couple of years ago my wife had to have spinal surgery in Miami and we came to the same conclusion about the nurses. We found that the night nurses were invariably the worst nurses, but they were also the worst people. Rude pushy automatons who obstinately moved through their shift so they could go home. They were atrocious. It kind of makes sense because you’d figure the better nurses would move up the ranks to the day shift. The day nurses were always polite and they at least communicated as if they cared, even if they didn’t (I couldn’t tell).


I couldn’t agree more! We just laid someone off here - a competent programmer, but he failed to communicate what he was doing, and he couldn’t understand the communications of others enough to apply them to what he was doing. His work was completely lacking in context, to the point where he wouldn’t realize when what he was doing was actually doing harm to the company (say, taking down a production server to work on code directly on the server.) He asked me for a reference - I told him I honestly couldn’t give him a good reference even though I knew he was familiar with certain languages inside and out. He just didn’t have the communication skills - the minimum level - to make it in the business world.


Many other puzzles @ http://technical-interview.com/puzzles.aspx


Probably my number one, top-of-the-list interview annoyance is interviewers who ask something unrelated, or only semi-related, to the position for which I’m applying.

For example, one interview I went to went something like this.
Interviewer: "Are you comfortable with writing MySQL queries?"
Me: “Yes.” (I had recently passed the MySQL Certified Associate exam and was studying for the Certified Developer exam at the time.)

Fortunately, having navigated several interviews by now and having marinated in MySQL Developer studies for weeks, I took this in stride and said, "That’s an administrator question. I’ve focused my study on development with MySQL. I’d be happy to answer… "

To refer back to your Phone Screen post, if I was interviewing at a PHP house and they asked me to write something in C++ or Java, I might just walk out (or at least feel like it.)


“what is the solution to this puzzle”?

There is no puzzle, just a statement of facts with no goal stated - as several people good at communicating have already stated.

All others have made various assumptions they weren’t asked to make. Those assumptions may be valid, or not, we’d need to ask more questions to determine what the requirements are.

By the way, I teach requirements elicitation and analysis to Master’s students at the ANU, so I better be good at this kind of thing.