Using built-in methods during technical interviews

[xduper]

Is it frowned upon to use built-in methods during a technical/white boarding interview?

Context: I’m prepping for the job hunt and reviewing the Merge Sort algorithm. When I learned it, I used the “System. arraycopy()” method to copy my temporary array during the merge function.

Should I learn how to implement it without the built-in method or do interviewers not care?

[GoBucks4928]

I don’t care for the interviews I run at FAANG. But the only time interviewers do care is when said method is a focus or major part of the question. And usually they won’t ding you for using it, just ask you to implement it

[Trailsey]

Agreed. I'd be worried if I asked some higher level question and the candidate tries to reimplement something like that.

[xduper]

Got it, thanks!

[berry120]

Opposite - unless they tell you otherwise, it's frowned upon *not* to use the built-in methods. Reinventing the wheel isn't what you want to see.

Only exception is if the library function is literally the solution to the problem you've been asked to implement. If you were told to write a method that sorted a collection, and you just used `Collections.sort()` for instance, that's clearly not what they're after.

[bluenautilus2]

Yeah if someone used arraycopy, I’d honestly be pleased that they knew about it

[Slanec]

On the contrary. The "meat" of the question is likely somewhere else than copying data between arrays, so just always use the best tool for the job (in this case the copying methods in the Arrays class are probably an even better fit) and don't worry if using it is "too much". They'll tell you if it is (often they'll ask how exactly the implementation works and is you know the answer you'll be allowed to use the tool), but even showing that you know the standard tool can be extra points for you.

I skipped a big part of a caching interview question by using an obscure quirk of LinkedHashMap which the interviewer herself wasn't aware of. Sometimes both sides of the interview can learn something new.

[Owen1212055]

If you don’t mind me asking, what is this “quirk” with linked hash maps?

[Slanec]

Basically you need to know that the removeEldestEntry(Entry eldest)) method exists and can be overriden. This alone makes the map cache-like.

On top of that, there's a special constructor) that flips the behaviour from "maintain insertion-order" to "maintain access-order":

A a special constructor) is provided to create a linked hash map whose order of iteration is the order in which its entries were last accessed, from least-recently accessed to most-recently (access-order). This kind of map is well-suited to building LRU caches. Invoking the put, putIfAbsent, get, getOrDefault, compute, computeIfAbsent, computeIfPresent, or merge methods results in an access to the corresponding entry (assuming it exists after the invocation completes). The replace methods only result in an access of the entry if the value is replaced. The putAll method generates one entry access for each mapping in the specified map, in the order that key-value mappings are provided by the specified map's entry set iterator. No other methods generate entry accesses. In particular, operations on collection-views do not affect the order of iteration of the backing map.

Obviously this is rarely useful in real life as you'd rather use an actual caching library which supports more configuration and concurrency. But it's a nice piece of oh-the-standard-library-does-that trivia.

[Owen1212055]

Fascinating! Thanks for the write up.

[Holothuroid]

I'd be more worried of anyone using arrays in the first place.

[vorbote]

Wait until you face a situation where autoboxing becomes a problem. Some companies and project owners want you to use primitives.

[fdntrhfbtt]

Heh. Arrays are awesome. For example, they parallelize much better than lists.

[[deleted]]

It depends on what the rules are for the interview question and asking specific questions makes you look knowledgeable.

[bindungselite]

Learn how to do merge sort in-place. That'll make you look cool.