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  • Sorting a list of numbers with modified cost

    - by David
    First, this was one of the four problems we had to solve in a project last year and I couldn’t find a suitable algorithm so we handle in a brute force solution. Problem: The numbers are in a list that is not sorted and supports only one type of operation. The operation is defined as follows: Given a position i and a position j the operation moves the number at position i to position j without altering the relative order of the other numbers. If i j, the positions of the numbers between positions j and i - 1 increment by 1, otherwise if i < j the positions of the numbers between positions i+1 and j decreases by 1. This operation requires i steps to find a number to move and j steps to locate the position to which you want to move it. Then the number of steps required to move a number of position i to position j is i+j. We need to design an algorithm that given a list of numbers, determine the optimal (in terms of cost) sequence of moves to rearrange the sequence. Attempts: Part of our investigation was around NP-Completeness, we make it a decision problem and try to find a suitable transformation to any of the problems listed in Garey and Johnson’s book: Computers and Intractability with no results. There is also no direct reference (from our point of view) to this kind of variation in Donald E. Knuth’s book: The art of Computer Programing Vol. 3 Sorting and Searching. We also analyzed algorithms to sort linked lists but none of them gives a good idea to find de optimal sequence of movements. Note that the idea is not to find an algorithm that orders the sequence, but one to tell me the optimal sequence of movements in terms of cost that organizes the sequence, you can make a copy and sort it to analyze the final position of the elements if you want, in fact we may assume that the list contains the numbers from 1 to n, so we know where we want to put each number, we are just concerned with minimizing the total cost of the steps. We tested several greedy approaches but all of them failed, divide and conquer sorting algorithms can’t be used because they swap with no cost portions of the list and our dynamic programing approaches had to consider many cases. The brute force recursive algorithm takes all the possible combinations of movements from i to j and then again all the possible moments of the rest of the element’s, at the end it returns the sequence with less total cost that sorted the list, as you can imagine the cost of this algorithm is brutal and makes it impracticable for more than 8 elements. Our observations: n movements is not necessarily cheaper than n+1 movements (unlike swaps in arrays that are O(1)). There are basically two ways of moving one element from position i to j: one is to move it directly and the other is to move other elements around i in a way that it reaches the position j. At most you make n-1 movements (the untouched element reaches its position alone). If it is the optimal sequence of movements then you didn’t move the same element twice.

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  • Best approach to cache Counts from SQL tables ?

    - by pixel3cs
    I would like to develop a Forum from scratch, with special needs and customization. I would like to prepare my forum for intensive usage and wondering how to cache things like User posts count and User replies count. Having only three tables, tblForum, tblForumTopics, tblForumReplies, what is the best approach of cache the User topics and replies counts ? Think at a simple scenario: user press a link and open the Replies.aspx?id=x&page=y page, and start reading replies. On the HTTP Request, the server will run an SQL command wich will fetch all replies for that page, also "inner joining with tblForumReplies to find out the number of User replies for each user that replied." select tblForumReplies.*, tblFR.TotalReplies from tblForumReplies inner join ( select IdRepliedBy, count(*) as TotalReplies from tblForumReplies group by IdRepliedBy ) as tblFR on tblFR.IdRepliedBy = tblForumReplies.IdRepliedBy Unfortunately this approach is very cpu intensive, and I would like to see your ideas of how to cache things like table Counts. If counting replies for each user on insert/delete, and store it in a separate field, how to syncronize with manual data changing. Suppose I will manually delete Replies from SQL.

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  • What does the length attribute do when set on the @Column JPA annontation?

    - by James McMahon
    What exactly does setting the length on a column do in JPA? @Column(name = "middle_name", nullable = false, length = 32) public String getMiddleName() { return this.middleName; } I understand that you can use the annotations to generate the database schema based on the entity objects, but does length do any sort of check or truncation when persistence happens, or it solely used for schema creation? I also realize that JPA can sit on top of various implementations, the implementation I am concerned with in this case, is Hibernate.

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  • PHP text parsing and / or make your own language?

    - by AlexanderJohannesen
    Been Googling around without finding much at all, so does anyone know of a class or library that helps you parse any sort of language, like a Domain Specific Language (I'm creating one, so I'm flexible in what the syntax and format can be) into either PHP code or some helpful struct or a class hiearchy or ... ? Anything goes at this point. :) I want to experiment with parsing text files into tokens, building up a small grammar and syntax library to express things like Business Natural Languages.

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  • How do you retrieve a list of logged-in/connected users in .NET?

    - by Engram
    Here's the scenario: You have a Windows server that users remotely connect to via RDP. You want your program (which runs as a service) to know who is currently connected. This may or may not include an interactive console session. Please note that this is the not the same as just retrieving the current interactive user. I'm guessing that there is some sort of API access to Terminal Services to get this info?

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  • SQL Server Maximum row size

    - by DannySmurf
    Came across this error today. Wondering if anyone can tell me what it means: Cannot sort a row of size 9522, which is greater than the allowable maximum of 8094. Is that 8094 bytes? Characters? Fields? Is this a problem joining multiple tables that are exceeding some limit?

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  • jQuery overlay not working in IE6, Opera

    - by Wild Thing
    Hi, I've been scratching my head for hours trying to figure this out. I have this page: http://173.203.72.190/default.aspx. On clicking 'Any Cuisine', a sort of overlay is supposed to open. It works fine in nearly all browsers except IE6 and Opera. In IE6 and Opera, the jQuery 'overlay' won't open. Anybody have any ideas why this might be?

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  • Data access layer using Linq to SQL

    - by Andrei Tanasescu
    I am building a c# - linq - sql server winforms/asp.net application, accessing a database. I would like my business logic layer to be easily testable, and that means not littering it with Linq database queries everywhere. What design patterns/ best practices are available for the following use cases - inserting/updating a new object - searching for an object - loading a bunch of related data into a sort of "presentation" object that could be displayed by various views ?

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  • How does one mirror a maven repository?

    - by Randy
    Our company would like to mirror our Maven 2 Repository inside of the Amazon network. What software should one use to do this? We have looked into a Wagon-S3 but that sort of functionality is not desirable... we want the artifacts to already be present when we are ready for a build.

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  • Using Variables for Class Names in Python?

    - by Sam McAfee
    I want to know how to use variables for objects and function names in Python. In PHP, you can do this: $className = "MyClass"; $newObject = new $className(); How do you do this sort of thing in Python? Or, am I totally not appreciating some fundamental difference with Python, and if so, what is it?

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  • Which web solution should I use for my project?

    - by BenIOs
    I'm going to create a fairly large (from my point of view anyway) web project with a friend. We will create a site with roads and other road related info. Our calculations is that we will have around 100k items in our database. Each item will contain some information like location, name etc. (about 30 thing each). We are counting on having a few hundred thousand unique visitors per month. The 100k items and their locations (that will be searchable) will be the main part of the page but we will also have some articles, comments, news and later on some more social functions (accounts, forums, picture uploads etc.). We were going to use Google AppEngine to develop our project since it is really scalable and free (at least for a while). But I'm actually starting to doubt that AppEngine is right for us. It seems to be for webbapps and not sites like ours. Which system (language/framework etc.) would you guys recommend us to use? It doesn't really mater if we know the language since before (we like learning new stuff) but it would be good if it's something that is future proof.

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  • Method parameters confusion

    - by elec
    Often time methods take more than 3 parameters which are all of the same type, eg. void mymethod (String param1, String param2, String param3) then it's very easy for the client to mix up the parameters orders, for instance inverting param1 and param2: mymethod (param2, param1, param3); ...which can be the cause of much time spent debugging what should be a trivial matter. Any tips on how to avoid this sort of mistake (apart from unit tests) ?

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  • Building IronRuby WPF GUIs

    - by Vlad
    This may be a silly question but I was under the impression that it was possible to use IronRuby and MS Visual Studio 2010 together to sort of build interfaces\edit XAML in one window and code ruby in the other? Is this only possible to do with C#, Basic and C++ ? I've browsed SO and seen some IronRuby snippets like this one: button1.click do |sender, args| MessageBox.show("Hello World!") end So it stands to reason you can create GUIs somehow, but is the visual gui creator not available for ironruby?

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  • is there a way to compress a GET string so it won't be so long?

    - by sct
    I need to compress a string so it is shorter for a GET method form. Is there any way to compress a string and it will be decrypted later? That way... ?error=LOTS OF STUFFLOTS OF STUFFLOTS OF STUFFLOTS OF STUFFLOTS OF STUFF is shorter in some sort of key ?error=somekey so I can get back the result later. Not using MySQL preferably. Anyone know a good method for this?

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  • finding long repeated substrings in a massive string

    - by Will
    I naively imagined that I could build a suffix trie where I keep a visit-count for each node, and then the deepest nodes with counts greater than one are the result set I'm looking for. I have a really really long string (hundreds of megabytes). I have about 1 GB of RAM. This is why building a suffix trie with counting data is too inefficient space-wise to work for me. To quote Wikipedia's Suffix tree: storing a string's suffix tree typically requires significantly more space than storing the string itself. The large amount of information in each edge and node makes the suffix tree very expensive, consuming about ten to twenty times the memory size of the source text in good implementations. The suffix array reduces this requirement to a factor of four, and researchers have continued to find smaller indexing structures. And that was wikipedia's comments on the tree, not trie. How can I find long repeated sequences in such a large amount of data, and in a reasonable amount of time (e.g. less than an hour on a modern desktop machine)? (Some wikipedia links to avoid people posting them as the 'answer': Algorithms on strings and especially Longest repeated substring problem ;-) )

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  • How do you open a file in C++?

    - by superjoe30
    I want to open a file for reading, the C++ way. I need to be able to do it for text files, which would involve some sort of read line function, and a way to do it for binary files, which would provide a way to read raw data into a char* buffer.

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  • [python] parsing a string based on specified identifiers

    - by jml
    Let's say that I have the following text: in = "one aaa two bbbb three cccc" I would like to parse this into a group of variables that contain notworking = ["one", "two", "three"] v1,v2,v3 = in.split(notworking) I know that the example above won't work, but is there some utility in python that would allow me to use this sort of approach? I know what the identifiers will be in advance, so I would think that there has got to be a way to do this... Thanks for any help, jml

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  • How can I wrap an executable on UNIX (SunOS) so that it is never run more than once at the same time

    - by user332815
    I have an executable (no source) that I need to wrap, to make sure that it is not called more than once at a time. I immediately think of some sort of queue wrapper, but how do I actually make it so that my wrapper is called instead of the executable itself? Is there a better way to do this? The solution needs to be invisible because the users are other applications. Any information/recommendations are appreciated.

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  • Eclipse: copy *only* the error message

    - by Patrick
    Can I copy only the error message from Eclipse Problems with instead of this entire message: Severity and Description Path Resource Location Creation Time Id 1120: Access of undefined property sort. clientApp/src Filters.mxml line 36 1270460218964 798 thanks

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  • Sorting a list of version strings

    - by Zack
    I have a list containing version strings, such as things: versions_list = ["1.1.2", "1.0.0", "1.3.3", "1.0.12", "1.0.2"] I would like to sort it, so the result would be something like this: versions_list = ["1.0.0", "1.0.2", "1.0.12", "1.1.2", "1.3.3"] The order of precendece for the digits should obviously be from left to right, and it should be decending. So 1.2.3 comes before 2.2.3 and 2.2.2 comes before 2.2.3. How do I do this in Python?

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  • Using routing (?) to make GET request in Rails so ID doesn't show

    - by ale
    I have a link in one view myapp/locations that goes to myapp/statistics?id=1 (statistics for location with ID 1) which works fine but it doesn't look pretty. I think I've seen people do this sort of thing without needing the ?id=1? I could use a POST but this is not RESTful. Is there a way I can use routing to allow the user to go to myapp/statistics?id=1 but have the user see myapp/statistics? Many thanks.

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  • How to implement a login page in a GWT app?

    - by Gatis
    My WebApp needs to authenticate user before allowing any sort of access. The scenario I'm trying to implement is a login page with username and password fields. Once user hits "send" button, a sign like "Verifing..." should be shown up while an RPC call verifies credentials. In case of success, load the main app screen. What is the best way to implement that?

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