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This question is about how to best approach a coding interview from a data structures point of view.
The way I see it, there are two different ways, I could implement a specific DS from scratch, initialise it and then use it to solve my problem, or simply use a library (I'm talking about Node.js here, but I guess this applies to other languages as well, at least those with some in-built support for DS) without worrying about the implementation and only focusing on how to use them to solve a problem.
In the first case, I'm also demonstrating that I can implement a specific DS from scratch, but at the same time I would need more time and there's some additional complexity. Instead, using a library would leave me more time to solve the actual problem, but some companies might take a dim view on this approach.
I know there's no silver bullet, and different companies will have different views, but what approach would you take if you could only pick one, and why?
Well it is always best to use the library but it is always better to know how common library functions work at least the basic ones.
For example, in many interviews Binary search is asked to be implemented instead of just using the library functions. This is because knowing the implementation adds some good concept which can be used in general problem solving like using the same concept in other divide and conquer algorithms.
In production level code we always look for the fail safe and properly tested library code.
You should pick available libraries, first hand. If needed, customize the behavior of already available libraries.
I've been reading the following paper
https://www.researchgate.net/publication/293043297_A_two-stage_algorithm_for_combinatorial_testing
I'm failing to understand how exactly the first stage develops. I understand
that the author is using the Best Extended algorithm, but I'm not sure
how each method is being developed, like the
initialize-last-column and compute-missing-tuples. Also, it looks like
I'm also not sure if I should already know the value for N. I hope someone
can enlighten me on the subject. My final task is to translate this into a
c# example.
I have a simple linear programming problem. After solving it, I get the correct result. I want to speed it up using hot-start feature of MOSEK, but I don't know how to set some parameters like "res.sol.bas.sku", "res.sol.bas.skn", .... I only know an initial solution, i.e, "res.sol.bas.xx", where the value of the variables are stored for a near to optimal solution. Is it possible for me to accelerate the engine using Hot start feature in this way!
Regards
You seem to using MATLAB. Did you read
http://docs.mosek.com/6.0/toolbox/node009.html#238393032
Does it solve the issue?
Back in college, only the use of pseudo code was evangelized more than OOP in my curriculum. Just like commenting (and other preached 'best practices'), I found that in crunch time psuedocode was often neglected. So my question is...who actually uses it a lot of the time? Or do you only use it when an algorithm is really hard to conceptualize entirely in your head? I'm interested in responses from everyone: wet-behind-the-ears junior developers to grizzled vets who were around back in the punch card days.
As for me personally, I mostly only use it for the difficult stuff.
I use it all the time. Any time I have to explain a design decision, I'll use it. Talking to non-technical staff, I'll use it. It has application not only for programming, but for explaining how anything is done.
Working with a team on multiple platforms (Java front-end with a COBOL backend, in this case) it's much easier to explain how a bit of code works using pseudocode than it is to show real code.
During design stage, pseudocode is especially useful because it helps you see the solution and whether or not it's feasible. I've seen some designs that looked very elegant, only to try to implement them and realize I couldn't even generate pseudocode. Turned out, the designer had never tried thinking about a theoretical implementation. Had he tried to write up some pseudocode representing his solution, I never would have had to waste 2 weeks trying to figure out why I couldn't get it to work.
I use pseudocode when away from a computer and only have paper and pen. It doesn't make much sense to worry about syntax for code that won't compile (can't compile paper).
I almost always use it nowadays when creating any non-trivial routines. I create the pseudo code as comments, and continue to expand it until I get to the point that I can just write the equivalent code below it. I have found this significantly speeds up development, reduces the "just write code" syndrome that often requires rewrites for things that weren't originally considered as it forces you to think through the entire process before writing actual code, and serves as good base for code documentation after it is written.
I and the other developers on my team use it all the time. In emails, whiteboard, or just in confersation. Psuedocode is tought to help you think the way you need to, to be able to program. If you really unstand psuedocode you can catch on to almost any programming language because the main difference between them all is syntax.
If I'm working out something complex, I use it a lot, but I use it as comments. For instance, I'll stub out the procedure, and put in each step I think I need to do. As I then write the code, I'll leave the comments: it says what I was trying to do.
procedure GetTextFromValidIndex (input int indexValue, output string textValue)
// initialize
// check to see if indexValue is within the acceptable range
// get min, max from db
// if indexValuenot between min and max
// then return with an error
// find corresponding text in db based on indexValue
// return textValue
return "Not Written";
end procedure;
I've never, not even once, needed to write the pseudocode of a program before writing it.
However, occasionally I've had to write pseudocode after writing code, which usually happens when I'm trying to describe the high-level implementation of a program to get someone up to speed with new code in a short amount of time. And by "high-level implementation", I mean one line of pseudocode describes 50 or so lines of C#, for example:
Core dumps a bunch of XML files to a folder and runs the process.exe
executable with a few commandline parameters.
The process.exe reads each file
Each file is read line by line
Unique words are pulled out of the file stored in a database
File is deleted when its finished processing
That kind of pseudocode is good enough to describe roughly 1000 lines of code, and good enough to accurately inform a newbie what the program is actually doing.
On many occasions when I don't know how to solve a problem, I actually find myself drawing my modules on a whiteboard in very high level terms to get a clear picture of how their interacting, drawing a prototype of a database schema, drawing a datastructure (especially trees, graphs, arrays, etc) to get a good handle on how to traverse and process it, etc.
I use it when explaining concepts. It helps to trim out the unnecessary bits of language so that examples only have the details pertinent to the question being asked.
I use it a fair amount on StackOverflow.
I don't use pseudocode as it is taught in school, and haven't in a very long time.
I do use english descriptions of algorithms when the logic is complex enough to warrant it; they're called "comments". ;-)
when explaining things to others, or working things out on paper, i use diagrams as much as possible - the simpler the better
Steve McConnel's Code Complete, in its chapter 9, "The Pseudocode Programming Process" proposes an interesting approach: when writing a function longer than a few lines, use simple pseudocode (in the form of comments) to outline what the function/procedure needs to do before writing the actual code that does it. The pseudocode comments can then become actual comments in the body of the function.
I tend to use this for any function that does more than what can be quickly understood by looking at a screenful (max) of code. It works specially well if you are already used to separate your function body in code "paragraphs" - units of semantically related code separated by a blank line. Then the "pseudocode comments" work like "headers" to these paragraphs.
PS: Some people may argue that "you shouldn't comment what, but why, and only when it's not trivial to understand for a reader who knows the language in question better then you". I generally agree with this, but I do make an exception for the PPP. The criteria for the presence and form of a comment shouldn't be set in stone, but ultimately governed by wise, well-thought application of common sense anyway. If you find yourself refusing to try out a slight bent to a subjective "rule" just for the sake of it, you might need to step back and realize if you're not facing it critically enough.
Mostly use it for nutting out really complex code, or when explaining code to either other developers or non developers who understand the system.
I also flow diagrams or uml type diagrams when trying to do above also...
I generally use it when developing multiple if else statements that are nested which can be confusing.
This way I don't need to go back and document it since its already been done.
Fairly rarely, although I often document a method before writing the body of it.
However, If I'm helping another developer with how to approach a problem, I'll often write an email with a pseudocode solution.
I don't use pseudocode at all.
I'm more comfortable with the syntax of C style languages than I am with Pseudocode.
What I do do quite frequently for design purposes is essentially a functional decomposition style of coding.
public void doBigJob( params )
{
doTask1( params);
doTask2( params);
doTask3( params);
}
private void doTask1( params)
{
doSubTask1_1(params);
...
}
Which, in an ideal world, would eventually turn into working code as methods become more and more trivial. However, in real life, there is a heck of a lot of refactoring and rethinking of design.
We find this works well enough, as rarely do we come across an algorithm that is both: Incredibly complex and hard to code and not better solved using UML or other modelling technique.
I never use or used it.
I always try to prototype in a real language when I need to do something complex, usually writting unit tests first to figure out what the code needs to do.
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When I am stuck with a problem:
I search Google for code snippets.
I look at isolating the problem, so that I can better explain it to others in order to get answers.
What search techniques do you use to find the solution to your problem?
I started asking questions in Stack Overflow.
What other techniques or methods do you follow, to fix the problem more quickly?
Go and do something else. No, really. I've found that putting the problem away in the back of my mind helps. I can't count the number of times I thought of a great solution to something I've been working on when I was working on something else, or watching TV, or eating. It seems your brain is still working on the problem in the background.
If that fails to solve your problem, try talking to someone. You'd be surprised how often others can give solutions to your problem that are so simple you'd facepalm.
Well there's:
Google
Google
Google
Stack Overflow
Google
Google
Maybe a book if I have one.
Seriously, I started (hobby) programming in the 1980s and even into the mid 90s you had to know things and have a technical library. Then Google came along and it's easier to Google something than it is to look up (bookmarked!) API documentation (Google "java stringbuilder" will get me there faster than navigating will) let alone an actual book (electronic or paper).
Most problems you're trying to solve have been solved before. Many times.
The rest of debugging comes down to decomposition, possibly unit testing (which is related to decomposition) and verifying your assumptions.
By "decomposition", I mean that your solution is structured in such a way that small pieces can be individually tested and readily understood. If you have a 7000 line method you're (probably) doing something wrong.
Understanding what assumptions you've made is key too so you can verify them. For example, when I started with PHP I wrote a piece of code like this:
$fields = $_SESSION["fields"]; // $fields is an associative array
$fields["blah"] = "foo";
and I was scratching my head trying to figure out why it didn't work (the array wasn't being updated next time I queried $_SESSION). I came from a Java background where you might do this:
Map fields = (Map)httpSession.get("fields");
fields.put("blah", "foo");
and that would most definitely work. PHP however copies the array. A working solution is to use references:
$fields =& $_SESSION["fields"]; // $fields is an associative array
$fields["blah"] = "foo";
or simply:
$_SESSION["fields"]["blah"] = "foo";
The last thing I'll say about debugging and writing robust code in general is to understand the boundaries of your solution. By this I mean if you're implementing a linked list then the boundary conditions will revolve around when the list is empty.
Explain the problem to a colleague, or write it down to describe it. That will makes you think a different way, from a different perspective. In order to be more accurate, and to describe the context of the problem, you'll step back, get a higher level view of the problem, you may find out think you overlooked something that is actually important.
Sometimes, you even find the explanation before ending your description.
My best friend for many years has been to jump on my bike and go home. Just getting away from the keyboard has solved many problems over the years for me.
If the problem lasts to the end of the day, I try and consciously lock the problem away for solving before I go to sleep.
I realise this sounds a bit out there, but it has been very common in my experience that I'll wake up with at least an alternate approach to the problem, if not the full-on solution. The idea is not to stress about it - but actively decide to solve it over night. That way you can go to sleep without worry.
I think eating well, regular exercise and good sleep are huge contributors to the problem-solving process.
Usually I'll try nut out the problem for a few hours or so, trying different things writing it on paper, making diagrams. If none of that works I'll usually work through the following options.
Put a sticky note on my monitor and keep going with something else
Glance at the note through out the next few hours to keep the problem in the back of my mind
Google for similar problems and the methods used
Consult a co-worker or a friend
Ask on a forum such as stackoverflow
Give up and design the problem away or design a way around the problem so it can be dealt with some other time and stick a TODO note at the site of said workaround
Don't forget Google Code Search
It's often best to clear your head by doing something other than programming for a little while. See this answer for an example - I did it while struggling with a particularly thorny bug, and when I came back to the problem I solved it in about a minute.
Usually I try to solve it until I go to sleep.. Sometimes I write on paper what the code is doing and then I divide it in pieces; I try to know how the variables of the program change when it's running.
Try solving a much smaller version of the problem first and see how you get on with that.
Once you've done that the bigger problem won't look so scary.
Ask yourself: is solving this particular tricky problem really important to what you doing?
For the purposes of your application (or whatever the big picture is) is there a similar but easier problem that you could address to accomplish broadly the same thing.
Normally, I would get pen and paper and try to work out the details of the problem there. If that doesn't help, Google. Failing that, I'd do something else for a while, or ask online. Worked for me so far.
The fact you are stuck might be a 'code-smell'. Suggesting that their is something wrong with the design or approach somewhere else. Try to put your finger on what's causing this and fix this instead.
When you come back to your problem it might no longer exist.
One more time, browse thru what I think might be relevant, then take nap.
There are two other answers which mention sleeping or napping, but this deserves more emphasis. It is now known that there's SERIOUS machinery in there which goes to work when you sleep. Google (( CBS SCIENCE SLEEP )) will get you to a great free video.
If I can't figure out how to solve the real problem, I try to consider a simplified version of the problem. To take a simple example: I recently had the problem of finding a set of shipping routes to get an item from point A to point B, when there is not necessarily a direct route from A to B, but there might be an A to C and then C to B, or A to C, C to D, and then D to B. (I'm sure the airlines and railroads do this all the time.) That was fairly complex, so I tried looking first at the simple case: a direct A to B. That was easy. Then consider how I'd handle it with one stop along the way. Then consider two stops. At that point I was able to see the pattern to a solution.
Solutions to a simplified version of the problem may end up being a part of the bigger solution, with some additional complexity wrapped around them. But even if not, the exercise of solving the easier problem often gives you ideas on how to solve the real problem.
The main techniques I use (should be followed in order so that you can reuse what you have done in previous steps to be more efficient):
Define your issue: Try to clearly define what's the problem, and what's expected. See 2 to help you.
Collect data about the bug: Log everything: your attempts, the expected result, the observed result. This will avoid the need to redo several times the same tests (because your mind cannot memorize it all), and probably help you see the bigger picture.
Reduce your problem. This is true in general for any abstract modelling of natural phenomenons, but it's even more true of programming, because programs are very complex entities. You should try to reduce your code to a minimal program that reproduces your issue. Automated tools exist.
Talk to someone: several anecdotes affirm than about 2/3 of the bugs are resolved just by talking about it. See the Helpful Teddy Bear anecdote. If you have previously reduced your program to a minimal program, and have a clear definition of your issue, both will be useful to your explanation.
Reach for collaborative help: search on Google and on StackOverflow, and post if you can't find anything that answers your problem (but first see 1, you must have a clear definition of your problem).
As you can see, I put the collaborative help as the last step, because you should only ask for help after you have clearly defined your issue and tried to reduce the problem and fix it by yourself. If you reach for collaborative help before having tried the previous steps, you will either end up with a poor help or figure it out by yourself as soon as you have posted.
Also you can be interested in the Coursera Software Debugging course, which also describes several automated debugging methods.
Go to the toilet.
You move, so your brain gets oxygen.
You relax, so you focus on other things.
Peeing for innovation! :)