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  • How to optimize shopping carts for minimal prices?

    - by tangens
    I have a list of items I want to buy. The items are offered by different shops and different prices. The shops have individual delivery costs. I'm looking for an optimal shopping strategy (and a java library supporting it) to purchase all of the items with a minimal total price. Example: Item1 is offered at Shop1 for $100, at Shop2 for $111. Item2 is offered at Shop1 for $90, at Shop2 for $85. Delivery cost of Shop1: $10 if total order < $150; $0 otherwise Delivery cost of Shop2: $5 if total order < $50; $0 otherwise If I buy Item1 and Item2 at Shop1 the total cost is $100 + $90 +$0 = $190. If I buy Item1 and Item2 at Shop2 the total cost is $111 + $85 +$0 = $196. If I buy Item1 at Shop1 and Item2 at Shop2 the total cost is $100 + $10 + $85 + $0 = 195. I get the minimal price if I order Item1 at Shop1 and Item2 at Shop2: $195 Question I need some hints which algorithms may help me to solve optimization problems of this kind for number of items about 100 and number of shops about 20. I already looked at apache-math and its optimization package, but I have no idea what algorithm to look for.

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  • Seperate compilation in C++

    - by Pat Murray
    Suppose you are creating a class with multiple .cpp files (which each contain the implementation of a member function) and have the class' declaration in a .h file. Also, each .cpp file includes the .h file via the include directive. I was told that if you change the implementation of any of the member functions (.cpp files) that you will have to recompile every .cpp file in order to run the program. That is, if I had 5 member functions (each implemented in a .cpp file) and I changed the implementation of 1 of the .cpp files I would have to compile the 1 .cpp file I changed AND the 4 other .cpp files I didn't change in order to correctly run my program. My question, if the previous statement is true, is why is the statement is true? Any insight on this concept would be helpful.

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  • Why doesn't MySQL support millisecond / microsecond precision?

    - by Byron Whitlock
    So I just found the most frustrating bug ever in MySQL. Apparently the TIMESTAMP field, and supporting functions do not support any greater precision than seconds!? So I am using PHP and Doctrine, and I really need those microseconds (I am using the actAs: [Timestampable] property). I found a that I can use a BIGINT field to store the values. But will doctrine add the milliseconds? I think it just assigns NOW() to the field. I am also worried the date manipulation functions (in SQL) sprinkled through the code will break. I also saw something about compiling a UDF extension. This is not an acceptable because I or a future maintainer will upgrade and poof, change gone. Has anyone found a suitable workaround?

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  • why don't more programming languages have builtin interfaces to the window manager?

    - by Naveen
    Programming is at the heart about automating tasks on a computer. Presumably those tasks would normally be done manually by a human. Humans use the computer through the keyboard, mouse, and interaction with the console or the window manager. But very few languages have built in functions that provide an interface to these basic computing objects. A notable exception is autohotkey, an open source language on windows, providing builtin functions that allow the following simple tasks: * Get Pixel Information * Get mouse position * Keyboard macros * Simulate key strokes * Simulate mouse click * Window management See examples on rosettacode. There have been various attempts on linux, many of which were stopped without explanation. One is the inactive tcl library: android. Search google code for android, lang:tcl

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  • After my laptop wakes up from sleeping/hibernating, the LCD/brightness is very low. How can I set it to default?

    - by meder
    In Power Management Preferences, On AC Power tab, I have brightness to 100%. "Dim display when idle" is not checked. I know for sure my LCD brightness is capable of going higher, because if I hit Fn and F7 then it resets the monitor brightness and settings for a few seconds, but the resolution breaks and then the brightness goes back. PS: OS is Debian Lenny ( I set the tags but for clarification ) and laptop is a Thinkpad.

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  • Multiple-File Template Implementation

    - by Maxpm
    With normal functions, the declaration and definition are often separated across multiple files like so: // Foo.h namespace Foo { void Bar(); } . // Foo.cpp #include "Foo.h" void Foo::Bar() { cout << "Inside function." << endl; } It is my understanding that this cannot be done with templates. The declaration and definition must not be separate because the appropriate form of the template is created "on-demand" when needed. So, how and where are templates typically defined in a multiple-file project like this? My intuition is that it would be in Foo.cpp because that's where the "meat" of functions normally is, but on the other hand it's the header file that's going to be included.

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  • Cross-reference of computers having virtualization technology [closed]

    - by msorens
    When considering obtaining a new computer one of my prerequisites is the ability to load Windows 8 in a virtual machine (using VirtualBox). A prerequisite for that is that the host computer have virtualization technology. I located an Intel cross reference of chips having virtualization technology but I am trying to find a "higher level" cross reference between computer models and virtualization technology availability, skipping the extra step of having to first look up what CPU chip is in a machine, then cross-referencing that on Intel's list.

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  • How to extract a single function from a source file

    - by Adam Matan
    Hi, I'm working on a small academic research about extremely long and complicated functions in the Linux kernel. I'm trying to figure out if there is a good reason to write 600 or 800 lines-long functions. For that purpose, I would like to find a tool that can extract a function from a .c file, so I can run some automated tests on the function. For example, If I have the function cifs_parse_mount_options() within the file connect.c, I'm seeking a solution that would roughly work like: extract /fs/cifs/connect.c cifs_parse_mount_options and return the 523 lines of code(!) of the function, from the opening braces to the closing braces. Of course, any way of manipulating existing software packages like gcc to do that, would be most helpful too. Thanks, Udi EDIT : The answers to Regex to pull out C function prototype declarations? convinced me that matching function declaration by regex is far from trivial.

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  • Change the value of an existing onclick function

    - by Mark Peach
    I have a page that is pulling in via an iframe a page of html content from a pre-existing content management system, whose content I can not directly change. I want to use jquery to alter some of the links and button locations dynamically. For links within the page I was able to change the href attr values of <a href="/content.asp">more</a> from content.asp to content2.asp using $("a[href^='/content.asp']") .each(function() { this.href = this.href.replace("content.asp", "content2.asp"); }); But the page pulled in also has form buttons that contains javascript onclick functions e.g. <INPUT type="button" value="Add to basket" onClick="document.location='/shopping-basket.asp?mode=add&id_Product=1076';"> I basically want to use jquery to select any such buttons and change the shopping-basket.asp to shopping-basket2.asp How can I select these buttons/onclick functions and change the location string?

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  • Get the first and last posts in a thread

    - by Grampa
    I am trying to code a forum website and I want to display a list of threads. Each thread should be accompanied by info about the first post (the "head" of the thread) as well as the last. My current database structure is the following: threads table: id - int, PK, not NULL, auto-increment name - varchar(255) posts table: id - int, PK, not NULL, auto-increment thread_id - FK for threads The tables have other fields as well, but they are not relevant for the query. I am interested in querying threads and somehow JOINing with posts so that I obtain both the first and last post for each thread in a single query (with no subqueries). So far I am able to do it using multiple queries, and I have defined the first post as being: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id LIMIT 0, 1 The last post is pretty much the same except for ORDER BY id DESC. Now, I could select multiple threads with their first or last posts, by doing: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id GROUP BY t.id But of course I can't get both at once, since I would need to sort both ASC and DESC at the same time. What is the solution here? Is it even possible to use a single query? Is there any way I could change the structure of my tables to facilitate this? If this is not doable, then what tips could you give me to improve the query performance in this particular situation?

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  • scala jrebel superclass change

    - by coubeatczech
    hi, I'm using JRebel with Scala and I'm quite frequently experiencing the need for restart of server due to the fact that JRebel is unable to load a class if the superclass was changed. This is done mainly when I change anonymous functions as I can deduce from the JRebel error desription: Class 'mypackage.NewBook$$anonfun$2' superclass was changed from 'scala.runtime.AbstractFunction1' to 'scala.runtime.AbstractFunction2' and could not be reloaded. Is there any way, how can I design my code to avoid this? Does scala compiler take the functions, numbers them from one as they appear in source code?

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  • Perl: How do I extract certain bits from a byte and then covert these bits to a hex value?

    - by Siegfried Hepp
    I need to extract certain bits of a byte and covert the extract bits back to a hex value. Example (the value of the byte is 0xD2) : 76543210 bit position 11010010 is 0xD2 Bit 0-3 defines the channel which is 0010b is 0x2 Bit 4-5 defines the controller which is 01b is 0x1 Bit 6-7 defines the port which is 11b is 0x3 I somehow need to get from the byte is 0xD2 to channel is 0x2, controller is 0x1, port is 0x3 I googled allot and found the functions pack/unpack, vec and sprintf. But I'm scratching by head how to use the functions to achieve this. Any idea how to achieve this in Perl ?

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  • How do I include 3rd party libraries in my code...

    - by Krakkos
    I understand the process of using a 3rd party library to access functions outside of my code base, but how do i actually set up Visual Studio 2005 to include them in the project. I have a 3rd party library with some headers, some cpp's, and some .lib files. In the projects properties I add the top level external library directory as an include directory, I add the additional library directory at the same level put this is project properties too. In the .cpp file where I use the functions, do I put the #include in its header file? In the top level projects header file? in the cpp? I've tried all that, but I get "unresolved external symbol"... grrrrrrrrrrrrr

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  • Need some explanation about MS Ajax using PageMethods

    - by Ahmed Said
    I have a project that uses PageMethods to call functions on the server. The server functions (written in C#) return the values as array of strings, without doing any kind of serialization and in the client side (from Js) the accessing of the return values is by using static variable called arguments. I found that sometimes for some users (cases are not repro) sometimes an exception occured "WebServiceFailedException the server method 'Foo' returned invalid data. the 'd' property is missing from JSON." Some searching on google I found that people are serializing the return values using DataContractJsonSerializer class and in js accessing the return value using one of the callback function Example: function OnRequestComplete(result, userContext, methodName) { var Person = eval('(' + result + ')'); alert(Person.Forename); alert(Person.Surname); } So is the first technique is correct? or what?

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  • Ruby integer to string key

    - by Gene
    A system I'm building needs to convert non-negative Ruby integers into shortest-possible UTF-8 string values. The only requirement on the strings is that their lexicographic order be identical to the natural order on integers. What's the best Ruby way to do this? We can assume the integers are 32 bits and the sign bit is 0. This is successful: (i >> 24).chr + ((i >> 16) & 0xff).chr + ((i >> 8) & 0xff).chr + (i & 0xff).chr But it appears to be 1) garbage-intense and 2) ugly. I've also looked at pack solutions, but these don't seem portable due to byte order. FWIW, the application is Redis hash field names. Building keys may be a performance bottleneck, but probably not. This question is mostly about the "Ruby way".

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  • How To Refactor If-else Code Segment?

    - by LostInLib
    I'm developing win8(metro style) application with Html5-js-jquery. I have this code segment; GetBoutiqueDetail: function (boutiqueId, options) { if (IsUserLogin()) { //different job A } else { ShowLoginPanel(undefined); } }, GetProductDetail: function (boutiqueId, productId, options) { if (IsUserLogin()) { //different job B } else { ShowLoginPanel(undefined); } }, AddBasket: function (productId, productVariantId, quantity, options) { if (IsUserLogin()) { //different job C } else { ShowLoginPanel(undefined); } },.... .And ~20 functions should check if user login or not. I should call functions like similar to "Library.GetBoutiqueDetail();" So my question is simple, how can I refactor that code to remove these if-else sections ?

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  • Missing something with Reader monad - passing the damn thing around everywhere

    - by Richard Huxton
    Learning Haskell, managing syntax, have a rough grasp of what monads etc are about but I'm clearly missing something. In main I can read my config file, and supply it as runReader (somefunc) myEnv just fine. But somefunc doesn't need access to the myEnv the reader supplies, nor do the next couple in the chain. The function that needs something from myEnv is a tiny leaf function. So - how do I get access to the environment in a function without tagging all the intervening functions as (Reader Env)? That can't be right because otherwise you'd just pass myEnv around in the first place. And passing unused parameters through multiple levels of functions is just ugly (isn't it?). There are plenty of examples I can find on the net but they all seem to have only one level between runReader and accessing the environment.

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  • How to get function's name from function's pointer in C?

    - by Daniel Silveira
    How to get function's name from function's pointer in C? Edit: The real case is: I'm writing a linux kernel module and I'm calling kernel functions. Some of these functions are pointers and I want to inspect the code of that function in the kernel source. But I don't know which function it is pointing to. I thought it could be done because, when the system fails (kernel panic) it prints out in the screen the current callstack with function's names. But, I guess I was wrong... am I?

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  • Does program need additional symbols from .so shared library except those declared in header file?

    - by solotim
    In C programming, I thought that a object file can be successfully linked with a .so file as long as the .so file offers all symbols which have been declared in the header file. Suppose I have foo.c, bar.h and two libraries libbar.so.1 and libbar.so.2. The implementation of libbar.so.1 and libbar.so.2 is totally different, but I think it's OK as long as they both offers functions declared in bar.h. I linked foo.o with libbar.so.1 and produced an executable: foo.bin. This executable worked when libbar.so.1 is in LD_LIBRARY_PATH.(of course a symbolic link is made as libbar.so) However, when I change the symbolic link to libbar.so.2, foo.bin could not run and complainted this: undefined symbol: _ZSt4cerr I found this symbol type is 'B' and it does not appear in libbar.so.2. Obviously this symbol has nothing to do with those functions I decared in bar.h. What's wrong here?

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  • T4MVC Optional Parameter Inferred From Current Context

    - by Itakou
    I have read the other post about this at T4MVC OptionalParameter values implied from current context and I am using the latest T4MVC (2.11.1) which is suppose to have the fix in. I even checked checked to make sure that it's there -- and it is. I am still getting the optional parameters filled in based on the current context. For example: Let's say I have a list that is by default ordered by a person's last name. I have the option to order by first name instead with the URL http://localhost/list/stuff?orderby=firstname When I am in that page, I want to go back to order by first name with the code: @Html.ActionLink("order by last name", MVC.List.Stuff(null)) the link I wanted was simply http://localhost/list/stuff without any parameters to keep the URL simple and short - invoking default behaviors within the action. But instead the orderby is kept and the url is still http://localhost/list/stuff?orderby=firstname Any help would be great. I know that in the most general cases, this does remove the query parameter - maybe I do have a specific case where it was not removed. I find that it only happens when I have the URL inside a page that I included with RenderPartial. My actual code is <li>@Html.ActionLink("Recently Updated", MVC.Network.Ticket.List(Model.UI.AccountId, "LastModifiedDate", null, null, null, null, null))</li> <li>@Html.ActionLink("Recently Created", MVC.Network.Ticket.List(Model.UI.AccountId, "CreatedDate", null, null, null, null, null))</li> <li>@Html.ActionLink("Most Severe", MVC.Network.Ticket.List(Model.UI.AccountId, "MostSevere", null, null, null, null, null))</li> <li>@Html.ActionLink("Previously Closed", MVC.Network.Ticket.List(Model.UI.AccountId, "LastModifiedDate", null, "Closed", null, null, null))</li> the problem happens when someone clicks Previously Closed and and go to ?status=closed. When they click Recently Updated, which I want to the ?status so that it shows the active ones, the ?status=closed stays. Any insight would be greatly appreciated.

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  • Forced naming of parameters in python

    - by Mark Mayo
    In python you may have a function definition: def info(object, spacing=10, collapse=1) which could be called in any of the following ways: info(odbchelper) info(odbchelper, 12) info(odbchelper, collapse=0) info(spacing=15, object=odbchelper) thanks to python's allowing of any-order arguments, so long as they're named. The problem we're having is as some of our larger functions grow, people might be adding parameters between spacing and collapse, meaning that the wrong values may be going to parameters that aren't named. In addition sometimes it's not always clear as to what needs to go in. We're after a way to force people to name certain parameters - not just a coding standard, but ideally a flag or pydev plugin? so that in the above 4 examples, only the last would pass the check as all the parameters are named. Odds are we'll only turn it on for certain functions, but any suggestions as to how to implement this - or if it's even possible would be appreciated.

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  • Compiler reordering around mutex boundaries?

    - by shojtsy
    Suppose I have my own non-inline functions LockMutex and UnlockMutex, which are using some proper mutex - such as boost - inside. How will the compiler know not to reorder other operations with regard to calls to the LockMutex and UnlockMutex? It can not possibly know how will I implement these functions in some other compilation unit. void SomeClass::store(int i) { LockMutex(_m); _field = i; // could the compiler move this around? UnlockMutex(_m); } ps: One is supposed to use instances of classes for holding locks to guarantee unlocking. I have left this out to simplify the example.

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  • boost::unordered_map is... ordered?

    - by Thanatos
    I have a boost::unordered_map, but it appears to be in order, giving me an overwhelming feeling of "You're Doing It Wrong". Why is the output to this in order? I would've expected the underlying hashing algorithm to have randomized this order: #include <iostream> #include <boost/unordered_map.hpp> int main() { boost::unordered_map<int, int> im; for(int i = 0; i < 50; ++i) { im.insert(std::make_pair(i, i)); } boost::unordered_map<int, int>::const_iterator i; for(i = im.begin(); i != im.end(); ++i) { std::cout << i->first << ", " << i->second << std::endl; } return 0; } ...gives me... 0, 0 1, 1 2, 2 ... 47, 47 48, 48 49, 49

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