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  • Algorithm possible amounts (over)paid for a specific price, based on denominations

    - by Wrikken
    In a current project, people can order goods delivered to their door and choose 'pay on delivery' as a payment option. To make sure the delivery guy has enough change customers are asked to input the amount they will pay (e.g. delivery is 48,13, they will pay with 60,- (3*20,-)). Now, if it were up to me I'd make it a free field, but apparantly higher-ups have decided is should be a selection based on available denominations, without giving amounts that would result in a set of denominations which could be smaller. Example: denominations = [1,2,5,10,20,50] price = 78.12 possibilities: 79 (multitude of options), 80 (e.g. 4*20) 90 (e.g. 50+2*20) 100 (2*50) It's international, so the denominations could change, and the algorithm should be based on that list. The closest I have come which seems to work is this: for all denominations in reversed order (large=>small) add ceil(price/denomination) * denomination to possibles baseprice = floor(price/denomination) * denomination; for all smaller denominations as subdenomination in reversed order add baseprice + (ceil((price - baseprice) / subdenomination) * subdenomination) to possibles end for end for remove doubles sort Is seems to work, but this has emerged after wildly trying all kinds of compact algorithms, and I cannot defend why it works, which could lead to some edge-case / new countries getting wrong options, and it does generate some serious amounts of doubles. As this is probably not a new problem, and Google et al. could not provide me with an answer save for loads of pages calculating how to make exact change, I thought I'd ask SO: have you solved this problem before? Which algorithm? Any proof it will always work?

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  • Map Reduce Frameworks/Infrastructure

    - by Johannes Rudolph
    Map Reduce is a pattern that seems to get a lot of traction lately and I start to see it manifest in one of my projects that is focused on an event processing pipeline (iPhone Accelerometer and GPS data). I needed to built a lot of infrastructure for this project, in fact it overweighs the logic code interacting with it by 2x. Some of the components I built where EventProcessors (with in- and output plus buffering, timing etc.), multiplexers and aggregators. This leads me to my question what the "common" required infrastrucutre for map reduce is. Since I am working with .Net a lot I can see map reduce infrastructure built into the Framework and language constructs. Functional languages support this paradigm per se. It seems every language can be used with map reduce, some have better support than others, others again are built around that concept (e.g. Go). And there are Frameworks like Apache Hadoop to support map reduce.

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  • How do you get your self focused with so many distractions around? (which you can't or don't want to

    - by Teja Kantamneni
    This question is definitely for a programmer and is centric towards a programmer. But if somebody feels it should not belong here I would not mind deleting it. I don't think this need to go as a WIKI, but if feel like it is a WIKI, I can do that too. The Question is: As a programmer you have to keep yourself up to date with the latest technologies and for that every programmer will generally follow some technology blogs and some social networking sites like (twitter, FB, SO, DZONE etc), how to keep your self focused on the things and still want to follow the technology trends? No Subjective or argumentative answers, Just want to know what practices other fellow programmers do for this...

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  • Why is it useful to count the number of bits?

    - by Scorchin
    I've seen the numerous questions about counting the number of set bits in a insert type of input, but why is it useful? For those looking for algorithms about bit counting, look here: http://stackoverflow.com/questions/1517848/counting-common-bits-in-a-sequence-of-unsigned-longs http://stackoverflow.com/questions/472325/fastest-way-to-count-number-of-bit-transitions-in-an-unsigned-int http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer

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  • Easiest way to find the correct kademlia bucket

    - by Martin
    In the Kademlia protocol node IDs are 160 bit numbers. Nodes are stored in buckets, bucket 0 stores all the nodes which have the same ID as this node except for the very last bit, bucket 1 stores all the nodes which have the same ID as this node except for the last 2 bits, and so on for all 160 buckets. What's the fastest way to find which bucket I should put a new node into? I have my buckets simply stored in an array, and need a method like so: Bucket[] buckets; //array with 160 items public Bucket GetBucket(Int160 myId, Int160 otherId) { //some stuff goes here } The obvious approach is to work down from the most significant bit, comparing bit by bit until I find a difference, I'm hoping there is a better approach based around clever bit twiddling. Practical note: My Int160 is stored in a byte array with 20 items, solutions which work well with that kind of structure will be preferred.

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  • Does code in the constructor add to code in subclass constructors?

    - by Jeremy Rudd
    Does code in the constructor add to code in subclass constructors? Or does the subclass's constructor override the superclass? Given this example superclass constructor: class Car{ function Car(){ trace("CAR") } } ...and this subclass constructor: class FordCar extends Car{ function FordCar(){ trace("FORD") } } When an instance of FordCar is created, will this trace "Car" and "Ford" ??

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  • Why do static Create methods exist?

    - by GeReV
    I was wondering, why do static Create methods exist? For instance, why use this code: System.Xml.XmlReader reader = System.Xml.XmlReader.Create(inputUri); over this code: System.Xml.XmlReader reader = new System.Xml.XmlReader(inputUri); I cannot find the rationale for using one over the other, and can't find any relation between classes who use this construct over the other. Can anyone shed some light on this?

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  • Linear feedback shift register?

    - by Mattia Gobbi
    Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. So I wanted to write some small code for a program that worked like a LFSR. To be more precise, that somehow showed how a LFSR works. Here's the cleanest thing I could come up with after some lenghtier attempts (Python): def lfsr(seed, taps): sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor sr, xor = str(xor) + sr[:-1], 0 print sr if sr == seed: break lfsr('11001001', (8,7,6,1)) #example I named "xor" the output of the XOR function, not very correct. However, this is just meant to show how it circles through its possible states, in fact you noticed the register is represented by a string. Not much logical coherence. This can be easily turned into a nice toy you can watch for hours (at least I could :-) def lfsr(seed, taps): import time sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor print time.sleep(0.75) sr, xor = str(xor) + sr[:-1], 0 print sr print time.sleep(0.75) Then it struck me, what use is this in writing software? I heard it can generate random numbers; is it true? how? So, it would be nice if someone could: explain how to use such a device in software development come up with some code, to support the point above or just like mine to show different ways to do it, in any language Also, as theres not much didactic stuff around about this piece of logic and digital circuitry, it would be nice if this could be a place for noobies (like me) to get a better understanding of this thing, or better, to understand what it is and how it can be useful when writing software. Should have made it a community wiki? That said, if someone feels like golfing... you're welcome.

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  • How large a role does subjectiveness play in programming?

    - by Bob
    I often read about the importance of readability and maintainability. Or, I read very strong opinions about which syntax features are bad or good. Or discussions about the values of certain paradigms, like OOP. Aside from that, this same question floats about in my mind whenever I read debates on SO or Meta about subjective questions. Or read questions about best practices and sometimes find myself or others disagreeing. What role does subjectiveness play within the programming realm? Sometimes I think it plays a large role. Software developers are engineers in a way, but also people. A large part of programming is dealing with code that's human readable. This is very different from Math or Physics or other disciplines with very exact and structured rules. Here the exact structure and rules are largely up in the air, changeable on a whim, and hence the amount of languages in existence. And one person may find one language very readable, and another person may find their own language the most comforting. The same with practices. One person may not like certain accepted practices. I myself find splitting classes into different files very unreadable, for instance. But, I can't say rules haven't helped in general. Certain practices have and do make life easier. And new languages have given rise to syntax and structure that make life easier. There's certainly been a progression towards code that is easier to read and maintain even given a largely diverse group of people. So maybe these things aren't as subjective as I thought. It reminds me, in a way, of UI design. Certainly it's subjective, but then there's an entire discipline involved in crafting good UI and it tends to work. Is there something non-subjective about the ideas behind maintainability, readability, and other best practices? Is there something tangible to grasp when one develops a new language or thinks of new practices?

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  • Why do switch statements continue after case

    - by John W.
    After evaluating a case in a switch statement in Java (and I am sure other languages) the following case's are also evaluated unless a control statement like break, or return is used. I understand this is probably an implementation detail, but what is/are the reasons for having this functionality happen? Thanks!

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  • Cross-platform and language (de)serialization

    - by fwgx
    I'm looking for a way to serialize a bunch of C++ structs in the most convenient way so that the serialization is portable across C++ and Java (at a minimum) and across 32bit/64bit, big/little endian platforms. The structures to be serialized just contain data, i.e. they're pure data objects with no state or behavior. The idea being that we serialize the structs into an octet blob that we can store in a database "generically" and be read out later on. Thus avoiding changing the database whenever a struct changes and also avoiding assigning each data member to a field - i.e. we only want one table to hold everything "generically" as a binary blob. This should make less work for developers and require less changes when structures change. I've looked at boost.serialize but don't think there's a way to enable compatibility with Java. And likewise for inheriting Serializable in Java. If there is a way to do it by starting with an IDL file that would be best as we already have IDL files that describe the structures. Cheers in advance!

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  • Visualize compiler warnings

    - by christoffer
    I'm looking for a way to visualize compiler warnings and remarks, by annotating or otherwise showing which lines cause a report. This is much like a modern IDE like NetBeans or Eclipse already does, but I'd like to take output from several compilers (and other static code analysis tools) at once, and create one single annotation in order to get a better overview. The rationale is that we've seen some problems go completely undetected by, say, Visual Studio 2005, but accurately detected with a proprietary ARM compiler, and vice versa. Cross-referencing warnings could potentially locate problems better, but doing so completely manually is infeasible. Have you heard of such a tool? Could an open-source IDE like Eclipse be extended to use several compilers at once, or has it already been done?

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  • CodeGolf: Find the Unique Paths

    - by st0le
    Here's a pretty simple idea, in this pastebin I've posted some pair of numbers. These represent Nodes of a directed graph. The input to stdin will be of the form, (they'll be numbers, i'll be using an example here) c d q r a b b c d e p q so x y means x is connected to y (not viceversa) There are 2 paths in that example. a->b->c->d->e and p->q->r. You need to print all the unique paths from that graph The output should be of the format a->b->c->d->e p->q->r Notes You can assume the numbers are chosen such that one path doesn't intersect the other (one node belongs to one path) The pairs are in random order. They are more than 1 paths, they can be of different lengths. All numbers are less than 1000. If you need more details, please leave a comment. I'll amend as required. Shameless-Plug For those who enjoy Codegolf, please Commit at Area51 for its very own site:) (for those who don't enjoy it, please support it as well, so we'll stay out of your way...)

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  • What's the reason for leaving an extra blank line at the end of a code file?

    - by Lord Torgamus
    Eclipse and MyEclipse create new Java files with an extra blank line after the last closing brace by default. I think CodeWarrior did the same thing a few years back, and that some people leave such blank lines in their code either by intention or laziness. So, this seems to be at least a moderately widespread behavior. As a former human language editor -- copy editing newspapers, mostly -- I find that those lines look like sloppiness or accidents, and I can't think of a reason to leave them in source files. I know they don't affect compilation in C-style languages, including Java. Are there benefits to having those lines, and if so, what are they?

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  • Minimizing the number of boxes that cover a given set of intervals

    - by fortran
    Hi, this is a question for the algorithms gurus out there :-) Let S be a set of intervals of the natural numbers that might overlap and b a box size. Assume that for each interval, the range is strictly less than b. I want to find the minimum set of intervals of size b (let's call it M) so all the intervals in S are contained in the intervals of M. Trivial example: S = {[1..4], [2..7], [3..5], [8..15], [9..13]} b = 10 M = {[1..10], [8..18]} // so ([1..4], [2..7], [3..5]) are inside [1..10] and ([8..15], [9..13]) are inside [8..18] I think a greedy algorithm might not work always, so if anybody knows of a solution of this problem (or a similar one that can be converted into), that would be great. Thanks!

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  • What is your longest-held programming assumption that turned out to be incorrect?

    - by Demi
    I am doing some research into common errors and poor assumptions made by junior (and perhaps senior) software engineers. What was your longest-held poor assumption that was eventually corrected? For example: I at one point failed to understand that the size of an integer was not a standard (depends on the language and target). A bit embarrassing to state, but there it is. Be frank: what hard-held belief did you have, and roughly how long did you maintain the assumption? It can be about an algorithm, a language, a programming concept, testing, anything under the computer science domain.

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  • how to read an address in multiple formats like google maps

    - by ratan
    notice that on google maps you can input the address any way you like. as long as it is a valid address...google maps will read it. In some ruby book I had seen code snippet for something like this, but with phone numbers. Any ideas how this could be done for addresses? in language of your choice. EDIT: i dont care about a "valid" address. I just want to parse an address. so that 123 fake street, WA, 34223 would be an address and so will 123 fake street WA 34223

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  • How to use a DHT for a social trading environment

    - by Lirik
    I'm trying to understand if a DHT can be used to solve a problem I'm working on: I have a trading environment where professional option traders can get an increase in their risk limit by requesting that fellow traders lend them some of their risk limit. The lending trader will can either search for traders with certain risk parameters which are part of every trader's profile, i.e. Greeks, or the lending trader can subscribe to requests from certain traders. I want this environment to be scalable and decentralized, but I don't know how traders can search for specific profile parameters when the data is contained in a DHT. Could anybody explain how this can be done?

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  • Need some help understanding this problem about maximizing graph connectivity

    - by Legend
    I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. I am not sure if this is a really a problem but I somehow have a feeling that there might exist more than one order in which case, it is required to choose the best order. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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  • How to restrain one's self from the overwhelming urge to rewrite everything?

    - by Scott Saad
    Setup Have you ever had the experience of going into a piece of code to make a seemingly simple change and then realizing that you've just stepped into a wasteland that deserves some serious attention? This usually gets followed up with an official FREAK OUT moment, where the overwhelming feeling of rewriting everything in sight starts to creep up. It's important to note that this bad code does not necessarily come from others as it may indeed be something we've written or contributed to in the past. Problem It's obvious that there is some serious code rot, horrible architecture, etc. that needs to be dealt with. The real problem, as it relates to this question, is that it's not the right time to rewrite the code. There could be many reasons for this: Currently in the middle of a release cycle, therefore any changes should be minimal. It's 2:00 AM in the morning, and the brain is starting to shut down. It could have seemingly adverse affects on the schedule. The rabbit hole could go much deeper than our eyes are able to see at this time. etc... Question So how should we balance the duty of continuously improving the code, while also being a responsible developer? How do we refrain from contributing to the broken window theory, while also being aware of actions and the potential recklessness they may cause? Update Great answers! For the most part, there seems to be two schools of thought: Don't resist the urge as it's a good one to have. Don't give in to the temptation as it will burn you to the ground. It would be interesting to know if more people feel any balance exists.

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  • Code golf: Word frequency chart

    - by ChristopheD
    The challenge: Build an ASCII chart of the most commonly used words in a given text. The rules: Only accept a-z and A-Z (alphabetic characters) as part of a word. Ignore casing (She == she for our purpose). Ignore the following words (quite arbitary, I know): the, and, of, to, a, i, it, in, or, is Clarification: considering don't: this would be taken as 2 different 'words' in the ranges a-z and A-Z: (don and t). Optionally (it's too late to be formally changing the specifications now) you may choose to drop all single-letter 'words' (this could potentially make for a shortening of the ignore list too). Parse a given text (read a file specified via command line arguments or piped in; presume us-ascii) and build us a word frequency chart with the following characteristics: Display the chart (also see the example below) for the 22 most common words (ordered by descending frequency). The bar width represents the number of occurences (frequency) of the word (proportionally). Append one space and print the word. Make sure these bars (plus space-word-space) always fit: bar + [space] + word + [space] should be always <= 80 characters (make sure you account for possible differing bar and word lenghts: e.g.: the second most common word could be a lot longer then the first while not differing so much in frequency). Maximize bar width within these constraints and scale the bars appropriately (according to the frequencies they represent). An example: The text for the example can be found here (Alice's Adventures in Wonderland, by Lewis Carroll). This specific text would yield the following chart: _________________________________________________________________________ |_________________________________________________________________________| she |_______________________________________________________________| you |____________________________________________________________| said |____________________________________________________| alice |______________________________________________| was |__________________________________________| that |___________________________________| as |_______________________________| her |____________________________| with |____________________________| at |___________________________| s |___________________________| t |_________________________| on |_________________________| all |______________________| this |______________________| for |______________________| had |_____________________| but |____________________| be |____________________| not |___________________| they |__________________| so For your information: these are the frequencies the above chart is built upon: [('she', 553), ('you', 481), ('said', 462), ('alice', 403), ('was', 358), ('that ', 330), ('as', 274), ('her', 248), ('with', 227), ('at', 227), ('s', 219), ('t' , 218), ('on', 204), ('all', 200), ('this', 181), ('for', 179), ('had', 178), (' but', 175), ('be', 167), ('not', 166), ('they', 155), ('so', 152)] A second example (to check if you implemented the complete spec): Replace every occurence of you in the linked Alice in Wonderland file with superlongstringstring: ________________________________________________________________ |________________________________________________________________| she |_______________________________________________________| superlongstringstring |_____________________________________________________| said |______________________________________________| alice |________________________________________| was |_____________________________________| that |______________________________| as |___________________________| her |_________________________| with |_________________________| at |________________________| s |________________________| t |______________________| on |_____________________| all |___________________| this |___________________| for |___________________| had |__________________| but |_________________| be |_________________| not |________________| they |________________| so The winner: Shortest solution (by character count, per language). Have fun! Edit: Table summarizing the results so far (2012-02-15) (originally added by user Nas Banov): Language Relaxed Strict ========= ======= ====== GolfScript 130 143 Perl 185 Windows PowerShell 148 199 Mathematica 199 Ruby 185 205 Unix Toolchain 194 228 Python 183 243 Clojure 282 Scala 311 Haskell 333 Awk 336 R 298 Javascript 304 354 Groovy 321 Matlab 404 C# 422 Smalltalk 386 PHP 450 F# 452 TSQL 483 507 The numbers represent the length of the shortest solution in a specific language. "Strict" refers to a solution that implements the spec completely (draws |____| bars, closes the first bar on top with a ____ line, accounts for the possibility of long words with high frequency etc). "Relaxed" means some liberties were taken to shorten to solution. Only solutions shorter then 500 characters are included. The list of languages is sorted by the length of the 'strict' solution. 'Unix Toolchain' is used to signify various solutions that use traditional *nix shell plus a mix of tools (like grep, tr, sort, uniq, head, perl, awk).

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  • What kinds of problems are most likely to occur? (question rewritten)

    - by ChrisC
    If I wrote 1) a C# SQL db app (a simple program consisting of a gui over some forms with logic for interfacing with the sql db) 2) for home use, that doesn't do any network communication 3) that uses a simple, reliable, and appropriate sql db 4) whose gui is properly separated from the logic 5) that has complete and dependable input data validation 6) that has been completely tested so that 100% of logic bugs were eliminated ... and then if the program was installed and run by random users on their random Windows computers Q1) What types of technical (non-procedural) problems and support situations are most likely to occur, and how likely are they? Q2) Are there more/other things I could do in the first place to prevent those problems and also minimize the amount of user support required? I know some answers will apply to my specific platforms (C#, SQL, Windows, etc) and some won't. Please be as specific as is possible. Mitch Wheat gave me some very valuable advice below, but I'm now offering the bounty because I am hoping to get a better picture of the kinds of things that I'm most reasonably likely to encounter. Thanks.

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