I often come across code cobbled together over many years, and it often really is easier to write a new clean implementation than keep patching the old stuff.

I know this is an old post, but I’m hoping you get notified of followups. I was just curious about your answer.

How do you rewrite code from scratch if you don’t know what it does?

I invariably get asked in interviews to decipher some badly written/unnecessarily cryptic piece of code. In one interview I tried pushing back:

Me: I would never write that kind of code.

Interviewer: well, assume someone else wrote it and you needed to debug it.

Me: Don’t you have coding standards? Code inspections? I doubt that code would pass.

Interviewer: Look, let’s say we didn’t have time to do an inspection. What does the code do?

Me: Well, in that case I probably haven’t got time to decipher someone else’s bad code, I would rewrite it from scratch.

I was not offered the job.

Tickletux did NOT say make a hire or no hire decision based on this question. Tickletux did not say “NO HIRE” if you don’t like the answer to the question. Tickletux did not say the question or the answer had any particular significance. He said just one thing, and on the basis of that one thing I know exactly how to evaluate the solution in this post.

What Tickletux said was, “The question serves to weed out people who cannot program AT ALL.” His pass or fail for the question was whether you can make the code work in under fifteen minutes over the phone. The purpose was to NO INTERVIEW a candidate if they are unable to answer the question. But if they do answer teh question correctly, they win an interview, not a job, so you use the interview to discover whether they are bored, smart, prone to showing off, like to have fun, or enjoys writing the obscure.

It doesn’t matter to me why the candidate would write the above code, or how it works. It just matters whether it works and whether the candidate was able to whip it up in fifteen minutes or less.

If you want to draw a lot of conclusions about what kind of production code the candidate would write, you need to modify the question, such as “write the code EXACTLY AS YOU WOULD IN PRODUCTION.” Then you can spend all day talking about the unit tests, comments, brace placement, and so forth.

Why have this incredibly complex hidden agenda behind a phone screen question?

  4#.|.(-.*3|i.15)++:-.*5|i.15
19142723

(no, I don’t feel like explaining J today)

Then it’s simply a matter of choosing between the four alternatives after right shifting this large number by twice i (modulo 15) and using the two rightmost bits only.

It’s an interesting idea: you could have them refactor that code to make it more obvious.