Interview - Program on Computer

Question

Spent some time searching, couldn't find exactly what I'm after.

We like giving hands-on programming exercises as part of the interview process. The interviewee gets a laptop, with the editor and compiler of his choice. He or she then get a programming exercise and has about an hour to code it. Depending on the nature of the question, internet access is either allowed or forbidden.

I'm looking for good general questions for a junior developer. I don't care what language they choose to program in. C++ is as good as Python or Scheme, as long as (s)he can program in it (this rules out "can you write a correct copy-constructor" style questions). I just want to see how they code, if their code is self-documenting, if they write tests, check edge-cases, etc.

What kind of questions would you ask?

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edit: The questions should be simple. I'd probably go with a question I can solve well in no more than 20 minutes. However, this is not the first stage in the interview process, and I can assume the person in front of me knows how to program.

Example question:

c is a complex number.
Z(n+1) = Z(n)^2 + c
Z0 = 0
c belongs to the set M iff |Z(n)| < 2 for all natural n

For all c between (-2, -i) to (2, i), print:
'X' if c is in M
'.' otherwise

This looks like a scary mathematical problem, but it's actually very easy, and can be coded in under 10 minutes. Once you get the correct answer, it is visually obvious that you have the correct solution

edit: If the candidate doesn't remember his complex numbers, I show them everything they need about it. I want to see if they can look at a scary problem, and know which questions to ask. For example, you have to use SOME_BIG_NUMBER in the partial solution below

def isInSet( c ):
    z_n = complex(0, 0)
    for i in range(1, SOME_BIG_NUMBER):
        z_n = z_n**2 + c
        if abs(z_n) > 2:
            return False

    return True

Answer 1

As difficult as this is to believe, you can make the desired test program pretty damned simple and still have most of your prospects fail the test. Even something as simple as the "FizzBuzz" thing can weed out an astonishing number of "programmers" who can't code.

Yes, it really is that bad out there.

Answer 2

Definitly something that would require to use recursion.

Also, implementing some very basic data structures (like stack or queue) may be a good idea.

Another thing that comes to mind is some simple task that requires reading documentation on some API and using it.

Or maybe something like giving description of an algorithm and asking to implement it. For example heapsort.

Answer 3

Open a file and print it out to the console.

A friends' company used to do this and most people fail the test. I think it's a great weed out question, you're either competent and it takes 3-5 minutes (accounting for nervousness here), or you're incompetent and you'll never get it done.

This is very fair if the interviewee gets to do this in a language of his choice, and it's not some weird contrived puzzle.

Answer 4

Try something like a simple hangman game, or a "higher or lower" guessing game.

Answer 5

In a recent recruiting process I've been involved with, less than 20% of the candidates could write a factorial() function (we required that they write both a recursive and a non-recursive version). I think this is a really low bar, so you can start with this and then increase the difficulty of the test.

Answer 6

Why not give them some problem they'd actually face while on the job? One of the few times I was given a test like this, the problem was to describe what a piece of code did and find the bug in it. The code was something they had pulled from their actual codebase and the bug was non-trivial but pretty easy to spot if you knew what to look for (in one case a character string might not be null-terminated, IIRC). Once that part was over, it led naturally into a discussion of what they were doing and the kind of problems they were working on.

Answer 7

If you want to give programming questions then there are lot of online judges loaded with tons of questions. You can select some questions from there and morph them or modify them slightly. you can have various questions with varying difficulty level too as your interview level go up.

Some online judges are :

• Topcoder,
• UVA online judge,
• Codechef,
• SPOJ Online,
• Project Euler,
• Ural OJ,
• Saratov OJ,
• ZJU OJ,
• Official ACM Live Archive,
• Peking University Online Judge,
• Programming Challenges.

You will get very good questions on programming, data structure, algorithms and maths.

Answer 8

You can also maybe make some question regarding the understanding of reference-semantics.

Answer 9

IIRC, I was given a function like the one below and I had to improve it.

/* C language. The actual arrays were bigger */
char mapping(char ch)
{
    static char *arr1 = "ABCDEF";
    static char arr2[6] = {128, 129, 130, 131, 132, 133};
    BOOL found = FALSE;

    for (int i = 0; i < 6; i++)
        if (ch == *(arr1+i)) {
            found = TRUE;
            break;
        }
    return found? arr2[i] : ch;
}

The real function was doing character mapping between two different code pages.

Answer 10

I had this as a recent programming example:

Generate a list of integers from 1 to 10,000 with each value appearing in the list once in a random order.

Now, this is really simple and vague, but that may well be part of the exercise, figuring out how to overcome the various shortcomings as someone could build a console application, winforms application, web page, web service or possibly something else that does this but the idea is to have something that should be simple and straightforward and see where they go with it.