Re: interview question on primes

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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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
.

Relevant Pages

  • Re: interview question on primes
    ... given two integers A and B, find all primes between them. ... loops over all numbers between 2 and sqrtto see if i%num == 0, ... was expected to solved right then and there, at the interview. ... the applicant can always _ask_ the interviewer about the ...
    (sci.math)
  • Re: interview question on primes
    ... given two integers A and B, find all primes between them. ... loops over all numbers between 2 and sqrtto see if i%num == 0, ... was expected to solved right then and there, at the interview. ... the applicant can always _ask_ the interviewer about the ...
    (sci.math)
  • Re: interview question on primes
    ... quasi wrote: ... given two integers A and B, find all primes between them. ... was expected to solved right then and there, at the interview. ... simple programming tasks during the interview. ...
    (sci.math)
  • Re: interview question on primes
    ... given two integers A and B, find all primes between them. ... loops over all numbers between 2 and sqrtto see if i%num == 0, ... They can't assume that the applicant is a Number ... research project out of it, ...
    (sci.math)
  • Re: finding primes
    ... find all primes between them. ... I basically wrote an initial function, bool isPrime, which ... loops over all numbers between 2 and sqrtto see if i%num == 0, ... force (all the mentioned solutions in this thread are brute force) for ...
    (comp.programming)