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Just speaking to points 1 and 2:

In an interview, there is an unspoken assumption that you won't be using third party libraries to implement algorithms, and certainly not a third party library that implements it in one function call. Using that as a red flag will yield a LOT of false positives.

Also, I have over 10 years experience in Java, have used Apache commons extensively, and had no idea that a string reversal method even existed. You can't use that knowledge to judge anything useful.

I agree about your unspoken assumption, but many interviewees ask. And the post I was responding to pointed to the Apache commons library, so I hazard to say it's not universally known.

A fail is not a red flag. A senior candidate not asking clarifying questions does not disqualify them (what I would call a red flag) but it is brought up in the debrief as a potential gap. I don't expect them to state this could be implemented using a single call to Apache commons. I call those candidates out in the debrief as being aware of the library, as a bonus. But not saying it isn't a negative.

If you're interviewing for some core, low level algorithm development then fair enough but I suspect if that's the case you could come up with something a little closer to the real life domain.

It's not that I think the question is too complicated, just not the best marker.

In my mind, more relevant questions are ones that demonstrate real life experience in the field. For example, populating a tree of objects in a high level language like Java from a DB where the tree of objects are stored as many to many relationships. You'd be surprised how many times I've run across production code which does this via SQL calls inside nested loops.

This whole infatuation with algorithm questions like you'd find in SICP might be good for new grads but misses the mark for Senior level engineers.

I asked a candidate to implement an algorithm that reverses a string. I don't see that as a complicated problem. It's literally a for loop, and based on how they choose to implement it you can ask about implications of append vs. prepend, etc.

I didn't ask them to implement dijkstra's algorithm, or even something as "hard" as breadth-first or depth-first search (which I feel any senior that deals with trees should be able to do).

It's a marker of this... Can the candidate solve a basic problem? Once they solve it, can they explain their solution? Do they understand the memory/time tradeoffs they chose? Do they know whether the code they wrote is thread-safe? If you don't feel a senior engineer should be able to answer those questions, to a very basic problem, how do you expect them to tackle something more complex?

What I'm interested in from a senior engineer is how many systems they've designed, implemented, deployed to production and supported in their careers and what their specific roles were in those projects. If I can't get an idea from their resume I wouldn't contact them for an interview.

As for the interview itself, well I've never needed to ask someone to reverse a string to determine if they're going to be of value with the criteria mentioned above.

But to be fair I've never worked on a project where implementing StringUtils.reverse() was required. If I were interviewing someone to work on Apache Commons or the JDK then I suppose that would be a relevant question.

Oh come on, argue the strongest part of their argument, would you, instead of nitpicking over string reverse. They've repeatedly, laboriously, explained that reversing a string isn't the relevant part to be focusing on.

What I'm interested in from a senior engineer is how many systems they've designed, implemented, deployed to production and supported in their careers and what their specific roles were in those projects. If I can't get an idea from their resume I wouldn't contact them for an interview.

And when their resume looks good and claims they are an expert, and you call them in and talk to them and they say they are an expert, and you start by opening a warmup question on the most basic levels of their expertise and they totally flunk it on multiple levels - unable to even handle the situation with tact or diplomacy in any way, are you still going to trust what they say about the systems they've "deployed and supported"?

Did you know in .Net strings are immutable? Neither did the guy at Google when he asked me to do some "in place" string fiddling algorithm or that guy at Amazon who wanted to reverse the strings in a sentence (yes there's a trick to that one found in some 80s programming book)

How many times in your job did you have to implement reversing a string without calling a library?

I mean, in languages like Python it can be as simple as `foo[::-1]` or some similar method. Anyone who can give a naive answer like that or

    usize len = strlen(foo);
    char* bar = malloc(len);
    for (int i = 0; i < len; i++) {
        bar[i] = foo[len - (i + 1)];
    }

and explain why that won't work for unicode strings, I imagine, would pass that particular fizzbuzz test. Bonus points for pointing out the null byte off by one error.

The only competent programmers I can think of that wouldn't be able to come up with that off the top off my head work in embedded or FPGAs where strings are rarely relevant.

I understand the class of rebuttal you're invoking here, but reversing a string is extremely easy - with or without a library. This is not an academic problem designed to see if a person can study prior to an interview. This is a first pass question designed to see if a person is even acquainted with basic programming. Any such question you could devise would be similarly patronizing or orthogonal to the exact work done on the job.

And yet, despite how easy the question is people still fail it. It's frankly absurd to me that a senior software engineer can fail this question. It's practically a freebie slam dunk for anyone with basic competency. Briefly drop that you can use your language's core function or method to do it. Then declare a new array and iterate through the string backwards, appending each character to the new array. When you're done, collapse the array to a string.

In other words, it's testing if you can write a for loop. How many times in your job do you expect to implement a for loop? I use for loops quite often.

> iterate through the string backwards

What about multi-byte characters?

That would be an excellent question to ask during an interview.

If you were interviewing with me, I'd ask you to do the (usually expected) ASCII/array-of-graphemes version first. If you did that, you'd pass, and get a positive shout-out in the feedback session for asking about multibyte chars.

If you, after solving the array-based form, had some ideas or even working code for how to handle multibyte characters directly, without falling back to the standard library of $language's idea of "what is an iterable character-equivalent unit in a string", and demonstrated similar insight in your other interview problems, I'd give a positive shout-out with the addendum that we might be interviewing you for the wrong (too junior) position.

In my experience, most people don't ask about multibyte chars. That's fine, if they solve the problem. It's not a positive or negative. If an interviewer is building questions with hidden "must-ask" gotchas like that, I think they're doing themselves and their candidates a disservice.

Something interesting does happen occasionally when candidates do ask about byte-width (or equivalent less-common but still very important gotchas like pointer/word size, endianness, etc. in relevant problems): some people ask the question, solve the naïve form of the problem, and then offer some thoughts as to how they'd handle the broader multibyte case. But some other people act as if knowing that gotcha means they won't or shouldn't have to continue solving the problem. I've had candidates tell me that they "figured it out" and wanted to go on to the next challenge at that point, without writing a line of code. I've had candidates tell me flat out that writing non-Unicode aware string processing algorithms was unrealistic and a waste of time, and that they wanted a problem that was more real-world or suited to their level of skill. Those things will also get you a shout-out in the interview review session, but not the good kind.

>>Then declare a new array and iterate through the string backwards, appending each character to the new array. When you're done, collapse the array to a string.

a. You can't iterate a 'String' backwards. You need to know the length first. And that requires traversing the string forwards at least once.

b. Once you reach the end you are wasting the effort of revisiting the elements, since you visited them already once.

c. A better option is build a build a double linked list, as you are traversing the list forward.

d. Once you have the double linked list ready, you have pointers to both start and end, and you traverse the way you like.

e. An even better way would be to design a data structure that contains all this meta data at String creation itself.

    Class CustomString {
        char* headPointer;
        char* tailPointer;
        int length;
        bool isPalindrome;
        char* string;
        /* Add your interview acrobatic things here */
    }

Stuff like this.

Now even though the answer in your comment is correct, they could reject you for not coming up with the answers I gave from point a through e above.

Now imagine some one telling you that, on these grounds, you don't know a semicolon worth programming and are probably a liar.

I hope you understand what's going on here. Every body can be rejected if they don't cut through your cookie cutter.

It was supposed to be in Java.

> a. You can't iterate a 'String' backwards. You need to know the length first. And that requires traversing the string forwards at least once.

That's not at all true in many languages. If a candidate asked "is this string's length known without an O(N) operation on the number of characters in it?" (or knew the answer for the default string constructs in the language they were using for the problem) I'd consider that a positive indicator. If they said what you just said, without consideration for the context, I'd consider that a negative.

This is not a case of someone expecting a given "cookie cutter" solution. Interviewers who do that are doing themselves and their candidates a disservice. This is a case where statements like "I know how strings work because I know how they work in $context" where $context is not what the interview expects you to work in will make a bad impression.

Can you traverse an array? Do you know that a string is an array? Do you know how the end or length of a string is represented in your language of choise? Do you know how each character is represented? Do you understand Unicode? Do you understand memory allocation? Is the string being reversed in place or you allocating a new string? What are the space and performance trade-offs between those approaches? I mean, you can fill a whole interview with just this topic. So yes if your answer is string.reverse() then expect some follow-up questions.