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Comment by suresk | Hacker News Reader

I don't see how reversing a string is a "puzzle" - I'd put its difficulty on par (or maybe slightly harder than) fizzbuzz. In most mainstream languages, it requires 2 pieces of knowledge:

1) That a string is implemented as an array of characters.

2) How to reverse an array.

The implementation is straightforward and should be trivial for just about anyone who's done much development.

I don't know that the question is that great, but it certainly isn't bad as a fizzbuzz-type question to use as a filter.

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Fair enough.

Here's my solution:

def reverse() {

    def a = "Can a fella get a job?"
    StringBuilder b = new StringBuilder()

    for (int i = a.length(); i > 0; i--) {
        b.append(a.charAt(i-1))
    }
    print b.toString()

}

But it doesn't use arrays because quite frankly, I haven't used an array in years. I despise the noise of the brackets. :-)

Seriously, I use ArrayLists instead of arrays. But even on this FizzBuzz lite exercise, I got tripped up. My "i > 0" was off by one. And I started down the path of a.substring, but that was a bad move. I quickly switched to charAt.

But about the only relevant piece of this: on an IDE, I was able to place a breakpoint, see where I'm at, what my variables look like, and make adjustments.

That's real life. My original cut of this would have disqualified me. Actually, even the cut above would disqualify me since I didn't use arrays.

But I need to confess. What you see above is literally the first time I've ever reversed a string in this manner. It's just not something I do. And it didn't roll off the tongue so to speak. I knew I had to process the string from the end and work backwards, but it still felt like trivia and not a substantive inquisition into my skills or experience.

Trivial? A bit. It took me about 5 min. The off by one was killing me. It hits you in two places: the i > 0 and the charAt(i-1).

That isn't a bad solution. You obviously hope that someone you're interviewing can come up with something like that fairly quickly, but I certainly wouldn't disqualify you based on your method of solving it or an initial off-by-one error.

> What you see above is literally the first time I've ever reversed a string in this manner. It's just not something I do.

There is a certain amount of value in that - seeing how someone reacts to and solves something they've never seen before. Can you come up with a reasonable plan for attacking the problem, implement it, test it to see if it works in a bunch of cases, and make the necessary adjustments?

To be fair, the coding you do in an interview is a bit artificial - the problems may not be typical and you are without the environment you are usually coding in. The good news is that it is a skill that you can work on and become better at, and it is usually worth doing so if you are pursuing a job and you know these kinds of things will come up. I don't think it is wasted effort either - I've been trying to work on my algorithm/data structure skills by solving interview-type problems, and I've noticed that the work I've been doing to learn to solve them better has been beneficial in my daily programming as well.

Your solution is fine, you've passed, flying colours. I might poke a bit around the edges to see if I can get you to say the word "array", but mostly out of interest.

The important bit is that this is not an assessment of your ability as a programmer, it's a negative filter: Are you one of these people who simply can't program, because if you can't, let's not waste any more of each others time.

Arrays. (Uhhg...I said it but I feel dirty.) ;-~

I've never liked arrays due to the brackets. But in a twist of irony, I now spend all day in Groovy and I use maps, thus brackets all the time. Yet I don't even notice.

So after carefully thinking about it, I now realize its not the brackets. I can't explain it. There's something about arrays I just despise despite having no similar ill will towards ArrayLists. They just feel so 70s.

Personally I much prefer a[i - 1] syntax over a.charAt(i - 1). The extra "charAt" seems noisy to me. But that's probably just my C background showing.

And at 1), you went wrong, in any language where strings are in unicode. Combining characters, byte order markers, surrogate pairs... And this is why I dislike the 'reversing a string' question. Because if you actually know anything about real world string handling, you know that correctly reversing a string is impossible, because there just isn't any logical way to reverse some constructs. How do you reverse a string which contains bidirectional control characters? What is the reverse of an optional line-breaking hyphen? Even simple things like parentheses might trip you up.

Once you really start thinking about reversing a string, you realise why it's so difficult to do robustly: because there is actually no logical reason to reverse a string.

As an interview question, I would only credit an interviewee for this question if they basically objected to the requirement in the first place, and explained how bad an idea it was - but since I wouldn't expect most interviewees to do that it would be a poor test to introduce in the interview.

That is a really good point and it complicates a lot of string-based questions, which is why they are almost always constrained (either implicitly or explicitly) by assuming that the string is ASCII only, which seems reasonable to me.

There are probably better filter questions to use that don't require as many artificial constraints.

Of course, in ASCII you can just reverse the bytes. Oh, until you come across a CRLF... Or a backspace... and it still makes no sense to even do it.

Reversing a string was initially a good interview question because in C you can keep probing multiple levels of knowledge with it. You learn if the interviewee knows the algorithm, then if they understand how to do it in place with a pointer, then if they understand the XOR pointer trick. It's not a very interesting problem in a language like Ruby or Python.

For that kind of language, what simple question do you suggest? My objective is test if the candidate have basic coding skills...

Dood....I checked your HN profile which led me to your blog. You're talking about decompiling Java code and bytecode diffing. That's hot. See, now that is dev stuff. That's hardcore. Love it.

Now, that was a puzzle :) It was pretty fun to diagnose, even if the knowledge isn't incredibly useful and probably a lot less impressive than it might look at fist glance. Figuring out how stuff works (and why it doesn't work like you think it should) is pretty fun - I wish I had more opportunities to do it.

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