Re: interview question on primes

quasi wrote:

On Mon, 25 Feb 2008 20:13:45 -0800, "1787" <nobody@xxxxxxxx> wrote:


"quasi" <quasi@xxxxxxxx> wrote in message
news:7ar6s39mvi8cgr09h9umkhhjb1r7gjp4l9@xxxxxxxxxx
On Tue, 26 Feb 2008 12:28:27 +1100, "Peter Webb"
<webbfamily@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:


"Digital Puer" <digital_puer@xxxxxxxxxxx> wrote in message
news:3bdc49e5-d202-491a-bde2-c7c31bee801f@xxxxxxxxxxxxxxxxxxxxxx
s.com...
Got this on a software engineering interview question:
given two integers A and B, find all primes between them.

I basically wrote an initial function, bool isPrime(int i), which
loops over all numbers between 2 and sqrt(i) to see if i%num ==
0, >>>> in which case the number is not a prime. With this function,
I then >>>> loop between A and B, calling isPrime() on each value.

Any better ideas?

The "correct" answer is heavily dependent on the range of
values of A and B,
and if this is all the question states, its a pretty poor
question.

No, not really.

It's a real world question, not an academic one.

Moreover, the question was not a "take-home project". Presumably it
was expected to solved right then and there, at the interview.

Judgement is required here.

Of course, the applicant can always ask the interviewer about the
range of values, but in my opinion, having to ask that question
would >> show a lack of common sense. The very fact that the range
was not >> specified, together with the implied time constraints of
the >> interview, should be enough for the applicant to opt for a
clean, >> simple, standard solution.

quasi

The OP was asked to find the primes between A and B. His answer
was essentially to write the simplest of all programs to determine
primality and test all the numbers between A and B. This is about
as far from a "real world" answer as you can get. He was obligated
to ask questions to more accurately determine the scope of the
problem. The useful answer then would be to suggest algorithms
that will actually find the primes for values of A and B
appropriate to their absolute and relative magnitudes. Peter Webb
(first responder to the OP's question) gets the job.

No he doesn't -- not if I'm hiring.

The fact is, most programmers in the world are bad ones.

Separating good from bad at interview time is not so easy, but a
simple challenger exercise, at the level of difficulty of the one
being discussed, is not so bad as a quick test, at least to filter out

(1) those who are incompetent mathematically

(2) those who have no design skills

(3) those who can't program their way out of a paper bag

(4) those who write overly complex code when the context of the
situation (interview time, on the spot) calls for simplicity.

quasi

Indeed. There is a very good argument made in this article:
http://tinyurl.com/yerwac for giving an interview candidate some very
simple programming tasks during the interview. The goal isn't to see
how the person accomplishes any real-life tasks (which would be
impossible to gauge in an interview timeframe), but just to see if he's
fluent in the very basics of programming. Can he write a strlen
function? Can he write a function to tell whether a string is all
caps? Etc. The thing to watch for is how *quickly* he writes the
code. A superstar will be able to write such code about as fast as he
can write. An inferior programmer will probably be able to write the
code, but it will take much longer.

--Mark
.

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