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I was wondering if anyone could please point me the right direction on how to approach the scheduling problem.
I have a teacher/student timetable problem, where I have teachers that teach certain subject at certain times and students that have preferences as of which class they want to take an when. The goal is to create a timetable not necessarily optimal solution.
I looked around here and there is a great number of discussions here on this website on this topic and the ones that I found go from super general to excessively difficult and I am currently unable to understand which programming/logic concepts to use to at least conceptualize the program work-flow.
Could anyone that dealt with similar problems explain how these types of problems are dealt with. I do not need the code (although pseudo-code would be awesome), but some guidelines ie step#1 - do this, step#2 - do that, step#3 - do etc....
Also, are there any libraries that are available that can do scheduling with preferences effectively and that have fairly straightforward inputs?
Many thanks!!
here is the outline of a problem that I have.
Let's say I have a group of salespeople:
The goal is to create a schedule that pairs buyer and seller subject to time availability and preferences.
This is a course time-tabling problem, right?
Can I accomplish with Drool Planner?
Take a look at the curriculum course scheduling problem which schedules lectures of teacher and students into timeslots and rooms. Take a look at my open source implementation in Java or just download and run the example.
I 've configured the construction heuristic First Fit Decreasing with the metaheuristic Tabu Search. I tried other configurations too, see my benchmarker config.
First you should make a list of resources for your problem. Then you should write down the constraints and set up a mathematical model. Finally you can use some optimization tool to generate solutions.
Of course this is not as easy as it seems to be. This page may give you some insight about possible solutions.
Matlab has a Global Optimization toolbox which lets you do genetic algorithm optimization with a very simple, point-and-click GUI that has helpful documentation. From what wikipedia says, your problem is just the kind to solve with a GA.
If you don't have access to the toolbox, you should be able to find genetic algorithm libraries for java, or worst comes to worst you can write your own. It won't be as extensive and it will take some work, but it shouldn't be terribly hard to make a simple one.
So for the summer I decided that I may as well start learning algorithms before school starts. I've been told that the class is fairly fast paced, and that algorithms isn't something you should take lightly (I have a tendency to do this with all the course work during the semester lol).
The book we're going to use is this Algorithms (4th Edition).
Anyway, this is my problem.
I'm almost third way through the book, but I just realized what I was doing. For example, I would read and re-read the sections I don't quite understand. Then if I feel confident enough, I would try to reproduce the same algorithm in java from my head. But by doing this, my code looks almost exactly like the ones in the book..in java.
I can't say I'm just memorizing code after code--I do understand the concepts and they help me code these algorithms--but I feel like I'll only be able to implement these algorithms in java. I should note that I only know java at the moment.
tldr: I'm learning algorithms as if I'm learning to play the guitar--repetition after repetition. But by doing so I feel like I'm being more fixated that I'll only able to implement these in java. How exactly would you learn algorithms if the book you're using is language-specific?
Thanks in advance.
Don't Confuse Yourself
You're studying Java, so write them in Java. Especially if Java is your first language. Don't confuse yourself for now, as you are trying to learn 2 things at once: how to progam in Java, and how to progam. You're learning both a new language and a way of thinking. Don't do too much but adding another language to the sauce for now.
Diversify
Later on, or if you feel confident enough that you can take on another language simultaneously, then it would obviously be beneficial to learn another one and try to replicate the algorithms without looking at the book.
Reproduce and Extend
What we could recommend you is to look for derivates of the algorithms. Known variants, that have been documented, and where you could just read the description of the variant so you can try to implement it from the "base" version, without needing to read the book.
For instance, if your book introduced you to a linked list, you should be able to come up with the algorithm for a doubly-linked list or a circular linked list without reading more than a description of the desired outcome. Or there's something about the original concepts that you clearly misunderstood.
Try First, Read-On Later
I'd recommend you actually even try to implement the algorithms described in your book before they show them to you. The point of seeing Sedgewick's algorithm is to see a canonical implementation, which is considered a standard blueprint. If you just read the section leading up to the implementation (which hopefully is displayed first), then just sit down with the book, and try to figure out how you could do that. If you can't do that at all, then you're too far ahead in your book and should backtrack and start again from scratch.
Thing about algorithms, they're essentially language-agnostic. There's really nothing stopping you from doing Sedgewick's examples in C, Python or some other language.
If you really don't know any other languages, concentrate on Java. Sure, its a bit repetitious, but those bits will stick in your head in a good way and come test time, you'll be glad for the information.
You're in an interesting position right now, since the kind of thinking required to write programs is very different from normal thinking. Add to that the fact you're learning a whole new language with a different syntax, punctuation and the like. Practice really does make perfect, since there are many bits and pieces to remember.
Oh, if you want practice with algorithms, try out project euler, code kata and other challenge sites. These little challenges can help you familiarize yourself with the language as well as get comfortable with the type of thinking required.
First, congrats on taking your first steps on learning how to code. I would say that you are already ahead of your peers by starting to look ahead during the summer.
As far as your fears on only being able to implement algorithms in Java, you have already demonstrated that it will not be a problem for you. It sounds like you are passionate enough to get started early so you should have no problem implementing a solution in multiple languages. Additionally most of the languages with C/C++ (Java and C# to name a few) like syntax will be similar enough that you will be able to translate your knowledge seamlessly.
The best advice that I can give is to CODE, CODE, CODE!! Don't just read about the algorithms actually implement them.
You don't say how well you know the mathematics behind the algorithms. That will be key in determining your facility with the code.
Sedgewick's books are very good. I'd feel free to pick some and check out other books as well, like "Numerical Recipes" and "Numerical Methods That Work". See if another point of view can clarify for you.
If you don't feel like you're getting enough out of copying Java, see if you can translate them into another language, maybe Python or purely functional alternative. If you can do that, you'll know you've got it.
I would either try to learn another language to verify that you can actually port it to another language (javascript would be my vote because it is simple and useful on the front and backend) or write the algorithms out in pseudocode since that is more language agnostic. Most languages will have the code look pretty similar. The only thing to be very careful about is when you are relying on some aspect of the language (such as generics or iterators in java) which you may not be able to use in another language and that could leave a gap in your understanding.
Another way to verify that you actually understand the algorithm is to make slight changes in the problem and make sure that you can adjust the algorithm to still work. For example if it is a sorting algorithm then try to sort by several different attributes rather than just one, if it is a graph algorithm make the graph a digraph and see how things should change.
I'm learning algorithms as if I'm learning to play the
guitar--repetition after repetition.
Then you are not learning algorithms. You are learning repetition. Two different things. The usage of a programming language by an algorithms book is a secondary factor. It is just a vehicle of instruction, an implementation detail.
What you should be focusing is on understanding the structure, logic and mathematical characteristics of an algorithm (and possibly the data structure(s) associated with it.)
That's what your focus should be.
But by doing so I feel like I'm being more fixated that I'll only able
to implement these in java.
But that is because you are focusing on just how the algorithm is being coded (in Java in this particular case.) You are focusing on an implementation detail.
When you learn to drive, you don't focus on how you learn to drive a Honda Civic or a Nissan Maxima. You learn the essence of what driving is, the rules of thumbs, the necessary precautions and the laws governing driving a vehicle.
Same with learning algorithms. You don't learn "Algorithms in Java" no more than "Algorithms in Haskell". You learn Algorithms first and foremost, the vehicle (sans very specialized cases) is secondary.
You should be focusing on what the algorithm does, how and why. Questions like "how/why does it work?" and most importantly *"what are the performance characteristics?", those are the things you should be focusing on.
Every good algorithms book (Sedgewick's included) carry that message. That's what you should focus on. How you get to that re-focusing, that's a function of one's personal learning strategies.
How exactly would you learn algorithms if the book you're using is language-specific?
By not focusing on the language. Focus on the structure, focus on the data structures involved, the invariants, pre-conditions and post-conditions. Understand asymptotic behavior described in Big-O (or Big-Omicron), Little-O/Little-Omicron and Omega notations.
You are learning algorithms, not programming in Java via coding algorithms.
If you can't do this mental leap, it means you do not have sufficient practice or abstract analysis. It is not an insult, but an observation and an advice. Coding, the usage of a programming language is typically secondary to the mathematical analysis of computing, the focus of Computer Science (of which Algorithms is a part thereof.)
NOTE I've done Java for over 10 years, and though I like it for work, I strongly believe it is a poor tool for learning programming or CS topics.
One is better served by learning Algorithms with either A) a procedural, systems-level programming language like C or Ada, or a high-level pseudo-assembler simulator, or B) a functional language like Lisp or Haskell.
Object-Oriented features in pure/pseudo-pure OO languages simply get in the way.
Algorithms are mathematical structures with a nature descriptive of the how (operationally) and/or the what (mathematically). The former is perfectly suited for procedural programming, the later for functional programming.
i am an student need to implement an top down parser for my mini project i confident understand the concept and i read the Wikipedia article but still i have some doubts can any one explain about top down parsing and how to implement it with a small example...
One of the things that students sometimes forget is that their professors are there to help them learn. If you've made a good attempt to understand top-down parsing and you haven't succeeded, then go and ask your professor to explain it. This is not an admission of weakness, and will not lose you marks. This is in fact what your professors are paid for. It's also what they like doing, or they wouldn't be in the job.
I didn't understand this when I was a student, and it cost me a whole lot of time and effort because I thought I would be penalized in some way if I admitted to not understanding something.
By "professor" I also mean teaching assistants or anyone else whose purpose is to help you learn.
top down parsing is parsing the way a normal human would do it. You describe high level terms in terms of lower level ones, until you get down to the basics. Here's a highly oversimplified example
public void parseSentence() {
parseNoun();
parseVerb();
}
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So do I really need to learn about them ? Isn't there an interesting way to learn about stacks, linked lists, heaps, etc ? I found it a boring subject.
**While posting this question it showed some warning. Am I not allowed to post such a question ? Admins please clarify and I will delete it :/
Warning :: The question you're asking appears subjective and is likely to be closed.
okay..I get it
So what is THE best way to learn them ? What book do I refer ? What website ?
It's compulsory to learn about data structures if you want to be a programmer. Data structures are your bread-and-butter - if you don't understand things like the behavior, uses, and run-time complexity ('big-O') of at least the basic structures (arrays, linked lists, stacks, queues, trees (binary / n-ary, self-balancing varietes), hash-tables, heaps, graphs) and the algorithms that run on them (insert / locate / delete), you won't know which is appropriate to use under what circumstances.
Every trade has its tools; these are ours. Data structures are the most basic underpinnings of almost any algorithm that you're going to learn. Unless you want to be a cargo cult programmer, you need to understand how they work.
Whether or not there are interesting ways to learn about them is a separate question entirely... :)
I would go even so far as to say that most of programming revolves around manipulating data structures, it is the foundation of computing after all: you get some data, you process it, you possibly give output. All the data usually reside in data structures and choosing inappropriate structures will have the bigger impact the bigger the project.
As you get more experience you will find that algorithms and datastructures are invaluable to your day-to-day development, and actually pretty interesting.
By learning about them now you will learn:
Which data structure is appropriate for which context, i.e. when to use a single-linked list, when to use a stack, when to use a queue, when to use a tree
Which algorithms are appropriate for which purpose, such as tree depth-first search or breadth-first search.
Space and time complexity of algorithms, for example why is a quicksort sometimes the best solution, and sometimes heapsort.
Overall it'll teach you the beginnings and fundamentals of computer science, even if you never have to implement a stack again you'll know the kind of thought and consideration that goes into it. If you then ever have to implement your OWN data structure (and chances are you will, quite often), you will know what to do and what not to do.
If you want to be a successful programmer, data structure is a must. How will you program if you don't know data structures and algorithms?
Whether you like it or not, all programming is built around data structures. You may never have to write one, but you will have to choose which one to use many times. It is not really a requirement to programming in general, but if you want to excel in the field, understanding of the basics is a must.
Anyone can build a shed without knowledge of materials or construction techniques. You can even work in a house placing bricks and mortar under the orders of someone else, but if you want to build a house yourself, you do need to understand materials and techniques.
Data structures are the programming materials. Algorithms are techniques. Will you use data structures? You will use the simplest ones in a daily basis, each so often you will need to solve a problem where an specific data structure is required, and while you may manage not to build your own bricks, you will need to understand whether you need bricks or a concrete wall for your purposes.
If you want some evidence for the importance of data structures, take a look at the Google hiring process. Whatever you think about Google as a company, there is no denying that they have some very good people working for them. Their interview process is setup to determine the candidates knowledge of data structures and algorithms. Because when it comes down to it, that is what is at the core of programming, no matter what language you are working in or what domain you are programming for.
If you are planning a career as a professional programmer, you need to know the fundamentals, not just how to crank out code that "works". Otherwise, your just playing.
Is it compulsory to learn about arithmetic to be an engineer?
If you take the attitude of "is it compulsory" with regards to any of the building blocks of programming languages, you're probably not cut out to be a coder. Regardless of "compulsory" or not, you should always be looking for new concepts to learn and seeing if it'll improve your coding style/standard.
But in answer to your question: yes.
I'd say it's compulsory at some point in your development to have a firm grasp. I'm not necessarily sure the standard Data Structures course is the best way to learn. Sometimes, the best way to learn them is "I have problem X. For some reason, it's taking my algorithm a long time to solve X. How can I make this faster?"
One book I'd highly recommend is Programming Pearls. It has some really good analyses, backed by a lot of examples of where the real-world motivations for the solutions came from. It presents the problems in an interesting manner, and never teaches by giving you a laundry list of data structures.
Yes 99% of books on Data Structures are boring and exercises contrived. They feel like they are just making up problems that server no practical purpose :(
This book is the one exception to the rule I've come across. You will have a naive but working RPG game by the end of the book:
Data Structures for Game Programmers
Read the above book and you will solve your chicken and egg problem and see you really can't do much without data structures after all.
Well, this may sound a little awkward but I wouldn't say it is COMPULSORY to learn Data Structures to be a - regular- developer. Seriously! Of courser if you study then hard it will give you a lot of insights and knowledge on several programming aspects and that's always good. But compulsory ... well, I think it is just too much. VERY GOOD would be enough.
Let me explain why. It is not that often, for today, to write Data Structures code because - let's face it - it would be RE-writing, RE-inventing what we already know for so many years! What I would say it is COMPULSORY is to study just the general theory of them and the APIs/libraries that are already commonly in use (and tested and optimized) like the Collections API in Java. You must know by heart the differences between a List and a Set (in Java for instance) and their capabilities and proper usage but you don't need to know exactly HOW they are implemented - checking every private method and attribute - to deal with most common, day to day, coding problems. You will do just fine without all the "guts" of Data Structures for the general stuff. We face different challenges now.
But don't get me wrong - neither think I am crazy or naive! Off course there are situations that you will need to implement yourself some sort of custom data structure (maybe your own BalancedBinaryTreeMap!). You got to be prepared for everything.
I am just arguing about being compulsory or not. Again, I don't think is compulsory but it is indeed very good.
Cheers.
I suppose you could learn programming without learning a whole lot about data structures or algorithms. To make an equivalent example, think of it like if a carpenter knew how to build things, but didn't know about measurements and such. Would he be able to get a career in carpentry? Possibly, but let's say he needed to know the exact material he would need to complete a project. He'd probably get fired because he doesn't know what sort of material or measurements to use.
So with data structures and algorithms, you can say it's the ability to give exact measurements of an application and knowing what sort of performance you'll get out it.
Like a musician learning scales, data structures are part of the tools of the software trade. Sure you can work as a programmer without the knowledge but you're handicapping yourself. If I'm interviewing two people for a position and one of them understands and uses structures and the other can't even explain what a stack is, my choice is pretty clear.
If you want to be judged to be a competent, employable programmer, you need to learn your craft.
Is it compulsory to learn them?
No, you can program without them, just as it's not compulsory to break your code into functions.
That being said, if you want to be an effective programmer that can write at least decent code without getting your car egged by your coworkers, you want to at least be able to make a decent selection of library classes.
Every programmer should understand the tradeoff between a LinkedList and an Array, or why binary searches and binary trees are useful for sorted data. This isn't just about performance - it's about correctness too since you can't just put anything into a tree set.
Does it mean that you need to know how to implement your own AVL tree, build super-smart data structures, etc.? Not necessarily. It's a matter of how much you want to know what's going on "beneath the hood" and whether your tasks necessitate it.
I'm not a big fan of deep data structure and algorithms questions in interviews because the vast majority of developers don't need to implement these things, just to use library stuff. I prefer to ask job related questions in interviews. However, accept that if you don't learn those things you would face a tougher battle to get other jobs.
It should be, yes...
No body should force you to learn anything you don't want to learn.
If you're the type of person that is compelled to be the best that he/she can be at what he/she does, and you love what you do for a living, you'll learn everything there is to know on your own accord.
#happysoul: You should ask yourself WHY learning data structures bore you. Also, it would help if you also identify what DOESN'T bore you.
If you at least love to learn about algorithms, I'm sure we can all suggest a perfect marriage of the two that would be exciting to learn!
My recommendation for best algorithm/data structure combo for the most fun learning experience: graphs.
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Ok so this isn't 100% programming question, for which I'm really sorry, but still this is the best place I know to ask it.
In ~2weeks time I'll have a job interview, first they'll make me take a test from Java and I was wondering what's the best way to prepare for it? I bet it will be something similar to SCJP (but probably much easier), are there any (short) books, tutorials that are worth reading? I did order the SCJP book by Sierra/Bates but I won't be able to read it before the test.
Don't get me wrong I do have experience with Java etc. but I really want to get the job so I want to go there well prepared.
Also marry Xmas to everyone, no matter what religion you are.
Don't get me wrong I do have
experience with Java etc. but I really
want to get the job so I want to go
there well prepared.
If you have enough experience don't worry about the test. Don't try to impress your next boss with an awesome test that does not reflect your current knowledge. Read Joel's posts about interviewing:
The second worst kind of interviewer
is the Quiz Show Interviewer. This is
the kind of person who thinks that
smart means “knows a lot of facts.”
They just ask a bunch of trivia
questions about programming and give
points for correct answers. Just for
fun, here is the worst interview
question on Earth: “What’s the
difference between varchar and
varchar2 in Oracle 8i?” This is a
terrible question. There is no
possible, imaginable correlation
between people that know that
particular piece of trivia and people
that you want to hire. Who cares what
the difference is? You can find out
online in about fifteen seconds!
Remember, smart does not mean “knows
the answer to trivia questions.”
Anyway, software teams want to hire
people with aptitude, not a particular
skill set. Any skill set that people
can bring to the job will be
technologically obsolete in a couple
of years, anyway, so it’s better to
hire people that are going to be able
to learn any new technology rather
than people who happen to know how to
make JDBC talk to a MySQL database
right this minute.
quoted from "The Guerrilla Guide to Interviewing (version 3.0)" by Joel Spolsky
If you need to impress someone to get the job, may be that's not a good place to work...
I recommend you pick up Effective Java, 2nd Edition by Joshua Bloch and read it cover to cover. It details several "best practices" for Java and will have you walking into the interview knowing for example things like:
when to use Static Factory Methods
when to use the Builder Pattern
what a Singleton is and how to enforce it
how to prevent instantiation of a class
why to avoid finalizers
the general contract for overriding equals and hashcode
to use accessor methods instead of public fields
to prefer lists to arrays
to favor generic types
to use enums instead of int constants
to return empty collections or arrays instead of null
to prefer for-each loops over traditional for loops
to avoid float and double if exact values are needed
beware of performance loss when doing string concatenation
refer to objects by their interfaces
Not to mention the other 40 or so topics that I can't remember off the top of my head. If you're able to talk about these topics and demonstrate an understanding, then there's no reason you shouldn't be in the running for the position since learning this material will already put you in the top 10 percentile of Java developers.
I have a little book with "Exam Cram" in its title. The emphasis is on "little;" you can read through it in a single evening. It describes in prose all the important features of Java, it contains tables of quick facts that will be essential, and it covers, briefly, all of the SCJP exam.
For the less than eidetic, it gives hints on how to write yourself a crib sheet from memory once the test starts (meaning you can carry a bit of what you need to know in short-term memory). There are also some tips on pitfalls and such. Finally, and perhaps most importantly, there is at least one practice exam in it (haven't looked at it in a while) and a bunch of drill questions.
Alas, from what I see at Amazon, the book I recommended only covers Java 2: http://www.amazon.com/Java-Exam-Cram-310-025/dp/1576102912 Still, there are bound to be similar, more timely books.
This one: http://www.amazon.com/SCJP-Certified-Programmer-Java-310-065/dp/0071591060/ref=sr_1_1?ie=UTF8&s=books&qid=1261601183&sr=1-1 by Kathy Sierra is similar and about Java 6.
Some people would (and in fact did) recommend buying a general purpose Java book. Ideally, all you should have to do is learn "all of Java" and then you'd be ready for the exam. But this is not a winning strategy!
related anecdote
The first time I took my driver's test with the DMV, I had a long wait and quickly skimmed through a little info booklet they provided. I easily scored 100.
I later had to take the test again. Knowing the test was laughably easy, I spurned the booklet and failed the theoretical test. The booklet didn't contain anything I didn't already know: But being by the same people who administer the test, it contained the same wording, it had similar situations from the test, it emphasized similar topics and situations. In a few minutes, it could easily make the difference between passing and failing.
Conclusion
Same approach with these "prepare for test XXX" books. It's a racket, but the special-purpose prep books work better at preparing you for the test than general knowledge (or general knowledge books) do.
May be you should read Eckel's Thinking in Java. In this book many specific java features are considered.
I would rather prepare my self to explain what I already know about java and how much I would like to work for that company.
While the programming knowledge is essential, I don't think you can improve much further in two weeks.
Better would be for you to prepare to answer, why do you want to work there, why should they hire you. etc.
My recommendation is HeadFirst Java to brush up on anything you may have some issues on. The SCJP is something that they may make you take upon hiring within 6 months for example, however I have never heard of a company making someone take a proctored test at an interview. Hope this helps.
Write something small but useful in Java, in whatever environment they're going to be using (applets, JSP, desktop...). That way you won't freeze trying to remember how to do e.g. console output.
If possible, show them some Java code you've obviously written and that you're proud of.
Brush up or learn the following :
Simple concepts e.g. static keyword, importance of equals and hashCode, etc.
How generics in java work?
How threading works, deadlock, race conditions, etc.
How java deals with memory. Can garbage collection be enforced?
Basics of OOP.
Basics of String, StringBuffer, StringBuilder, RuntimeException, etc.
Design patterns, e.g. singleton, visitor, etc.
If you want to know the language well then The Really Big Index will be invaluable. It's a huge list and you'd struggle to read it straight though but for a reference it's fantastic. Read it along with a set book like Thinking in Java or the SCJP book you've already ordered and you'll be absolutely fine.