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  • Ideas Related to Subset Sum with 2,3 and more integers

    - by rolandbishop
    I've been struggling with this problem just like everyone else and I'm quite sure there has been more than enough posts to explain this problem. However in terms of understanding it fully, I wanted to share my thoughts and get more efficient solutions from all the great people in here related to Subset Sum problem. I've searched it over the Internet and there is actually a lot sources but I'm really willing to re-implement an algorithm or finding my own in order to understand fully. The key thing I'm struggling with is the efficiency considering the set size will be large. (I do not have a limit, just conceptually large). The two phases I'm trying to implement ideas on is finding two numbers that are equal to given integer T, finding three numbers and eventually K numbers. Some ideas I've though; For the two integer part I'm thing basically sorting the array O(nlogn) and for each element in the array searching for its negative value. (i.e if the array element is 3 searching for -3). Maybe a hash table inclusion could be better, providing a O(1) indexing the element? For the three or more integers I've found an amazing blog post;http://www.skorks.com/2011/02/algorithms-a-dropbox-challenge-and-dynamic-programming/. However even the author itself states that it is not applicable for large numbers. So I was for 2 and 3 and more integers what ideas could be applied for the subset problem. I'm struggling with setting up a dynamic programming method that will be efficient for the large inputs as well.

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  • Does the order of columns matter in a group by clause?

    - by Jeff Meatball Yang
    If I have two columns, one with very high cardinality and one with very low cardinality (unique # of values), does it matter in which order I group by? Here's an example: select dimensionName, dimensionCategory, sum(someFact) from SomeFact f join SomeDim d on f.dimensionKey = d.dimensionKey group by d.dimensionName, -- large number of unique values d.dimensionCategory -- small number of unique values Are there situations where it matters?

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  • Twitter Trends API weekly.json causing error "Cannot use object of type stdClass as array"

    - by tucson
    I have the following PHP code: $ch = curl_init(); curl_setopt($ch, CURLOPT_URL,$URL); curl_setopt($ch, CURLOPT_RETURNTRANSFER,1); $result = curl_exec($ch); curl_close($ch); $obj = json_decode($result); foreach ($obj[0]->trends as $trend) echo utf8_decode($trend->name); which works fine for URL #1 (into the variable $URL): http://api.twitter.com/1/trends/1.json?exclude=hashtags but causes an error "Cannot use object of type stdClass as array" for URL #2: http://api.twitter.com/1/trends/weekly.json?exclude=hashtags I have searched for a while, but can't figure out a code to fix this and handle both URLs. Any help would be much appreciated.

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  • How to check null objects in jQuery

    - by Prashant
    I am using jQuery, I want to check existence of an element in my page. I have done following code, but its not working? if ($("#btext" + i) != null){ //alert($("#btext" + i).text()); $("#btext" + i).text("Branch " + i); } Please tell me what will be the right code? Thanks

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  • Should the code being tested compile to a DLL or an executable file?

    - by uriDium
    I have a solution with two projects. One for project for the production code and another project for the unit tests. I did this as per the suggestions I got here from SO. I noticed that in the Debug Folder that it includes the production code in executable form. I used NUnit to run the tests after removing the executable and they all fail trying to find the executable. So it definitely is trying to find it. I then did a quick read to find out which is better, a DLL or an executable. It seems that an DLL is much faster as they share memory space where communication between executables is slower. Unforunately our production code needs to be an exectuable. So the unit tests will be slightly slower. I am not too worried about that. But the project does rely on code written in another library which is also in executable format at the moment. Should the projects that expose some sort of SDK rather be compiled to an DLL and then the projects that use the SDK be compiled to executable?

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  • WCF high instance count: anyone knows negative sideffects?

    - by Alex
    Hi there! Did anyone experience or know of negative side effects from having a high service instance count like 60k? Aside from the memory consumption of course. I am planning to increase the threshold for the maximum allowed instance count in our production environments. I am basically sick of severe production incidents just because "something" forgot to close a proxy properly. I plan to go to something like 60k instances which will allow the service to survive using default session timeouts at a call rate average for our clients. Thanks, Alex

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  • CakePHP call to member function on non-object

    - by joec
    I have the following Model and Controller files, and when i visit this url, http://....../pois/index i get this error: Notice (8): Undefined property: PoisController::$Poi [APP/controllers/pois_controller.php, line 5] Fatal error: Call to a member function find() on a non-object in /home/joecoyle/public_html/app/controllers/pois_controller.php on line 5 The Model is this, called poi.php: <?php class Poi extends AppModel { } ?> And the controller is this, named pois_controller.php <?php class PoisController extends AppController { function index(){ $this->set('pois',$this->Poi->find('all')); } } ?> As i am new to CakePHP i am not sure what is causing this error, as everything seems to be named, right, and i am following the tutorial on the CakePHP site... Thanks

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  • adding a flash object to FancyBox using jquery swfobject

    - by Freeman
    Fellows, I dont seem to be getting a solution. I have a a video gallery which I create by dynamically from a database. I have managed to create a flash object which plays well without FancyBox, however I want a person to click on the gallery and then an swobject is created which will then be show on a fancybox. Here is part of my javascript which is not working. $.ajax({ data:"search=vids&id="+ art, type: "POST", url: "doyit.php", success: function(msg){ $(".videogallery").html('<h3>Click to view videos of '+name+'</h3>'+msg); $('.video').bind('click',function(ev){ var vid=$(this).attr("href"); var img=$(this).find("img").attr("src") $(this).flash({swf: "mediaplayer.swf", flashvars: { file: vid, image: img } }) $(this).fancybox( { ajax:{ type:"POST"}, 'padding' : 0, 'autoScale' : false, 'transitionIn' : 'none', 'transitionOut' : 'none', 'title' : this.title, 'width' : 680, 'height' : 495 } ); $(this).unbind(ev) return false; }) } Any suggestions?

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  • Grasp Controller, Does it really need a UI to exist?

    - by dbones
    I have a Domain model which can be in multiple states, and if these states go out of a given range it the domain should automatically react. For example I have a Car which is made of multiple things which have measurements the Engine - Rev counter and Temperature the Fuel Tank - capacity Is is plaseable to have a CarStateController, which observses the engine and the tank, and if these states go out of range IE the engine temperature goes above range, turn the engine fan on?? There is no UI, (you could argue it would show a light on the dash board, but for this case it does not) is this a valid use of a GRASP controller pattern? if not what is this CarStateController Called? Or have I completely missed the point and this should be the State Pattern?

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  • how to write a constructor...

    - by Nima
    is that correct to write a constructor like this? class A { A::A(const A& a) { .... } }; if yes, then is it correct to invoke it like this: A* other; ... A* instance = new A(*(other)); if not, what do you suggest? Thanks

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  • What is the most efficient way to store a mapping "key -> event stream"?

    - by jkff
    Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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  • fastest way to crawl recursive ntfs directories in C++

    - by Peter Parker
    I have written a small crawler to scan and resort directory structures. It based on dirent(which is a small wrapper around FindNextFileA) In my first benchmarks it is surprisingy slow: around 123473ms for 4500 files(thinkpad t60p local samsung 320 GB 2.5" HD). 121481 files found in 123473 milliseconds Is this speed normal? This is my code: int testPrintDir(std::string strDir, std::string strPattern="*", bool recurse=true){ struct dirent *ent; DIR *dir; dir = opendir (strDir.c_str()); int retVal = 0; if (dir != NULL) { while ((ent = readdir (dir)) != NULL) { if (strcmp(ent->d_name, ".") !=0 && strcmp(ent->d_name, "..") !=0){ std::string strFullName = strDir +"\\"+std::string(ent->d_name); std::string strType = "N/A"; bool isDir = (ent->data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) !=0; strType = (isDir)?"DIR":"FILE"; if ((!isDir)){ //printf ("%s <%s>\n", strFullName.c_str(),strType.c_str());//ent->d_name); retVal++; } if (isDir && recurse){ retVal += testPrintDir(strFullName, strPattern, recurse); } } } closedir (dir); return retVal; } else { /* could not open directory */ perror ("DIR NOT FOUND!"); return -1; } }

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  • Optimizing a shared buffer in a producer/consumer multithreaded environment

    - by Etan
    I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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  • How to decide on what hardware to deploy web application

    - by Yuval A
    Suppose you have a web application, no specific stack (Java/.NET/LAMP/Django/Rails, all good). How would you decide on which hardware to deploy it? What rules of thumb exist when determining how many machines you need? How would you formulate parameters such as concurrent users, simultaneous connections and DB read/write ratio to a decision on how much, and which, hardware you need? Any resources on this issue would be very helpful...

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  • STL find performs bettern than hand-crafter loop

    - by dusha
    Hello all, I have some question. Given the following C++ code fragment: #include <boost/progress.hpp> #include <vector> #include <algorithm> #include <numeric> #include <iostream> struct incrementor { incrementor() : curr_() {} unsigned int operator()() { return curr_++; } private: unsigned int curr_; }; template<class Vec> char const* value_found(Vec const& v, typename Vec::const_iterator i) { return i==v.end() ? "no" : "yes"; } template<class Vec> typename Vec::const_iterator find1(Vec const& v, typename Vec::value_type val) { return find(v.begin(), v.end(), val); } template<class Vec> typename Vec::const_iterator find2(Vec const& v, typename Vec::value_type val) { for(typename Vec::const_iterator i=v.begin(), end=v.end(); i<end; ++i) if(*i==val) return i; return v.end(); } int main() { using namespace std; typedef vector<unsigned int>::const_iterator iter; vector<unsigned int> vec; vec.reserve(10000000); boost::progress_timer pt; generate_n(back_inserter(vec), vec.capacity(), incrementor()); //added this line, to avoid any doubts, that compiler is able to // guess the data is sorted random_shuffle(vec.begin(), vec.end()); cout << "value generation required: " << pt.elapsed() << endl; double d; pt.restart(); iter found=find1(vec, vec.capacity()); d=pt.elapsed(); cout << "first search required: " << d << endl; cout << "first search found value: " << value_found(vec, found)<< endl; pt.restart(); found=find2(vec, vec.capacity()); d=pt.elapsed(); cout << "second search required: " << d << endl; cout << "second search found value: " << value_found(vec, found)<< endl; return 0; } On my machine (Intel i7, Windows Vista) STL find (call via find1) runs about 10 times faster than the hand-crafted loop (call via find2). I first thought that Visual C++ performs some kind of vectorization (may be I am mistaken here), but as far as I can see assembly does not look the way it uses vectorization. Why is STL loop faster? Hand-crafted loop is identical to the loop from the STL-find body. I was asked to post program's output. Without shuffle: value generation required: 0.078 first search required: 0.008 first search found value: no second search required: 0.098 second search found value: no With shuffle (caching effects): value generation required: 1.454 first search required: 0.009 first search found value: no second search required: 0.044 second search found value: no Many thanks, dusha. P.S. I return the iterator and write out the result (found or not), because I would like to prevent compiler optimization, that it thinks the loop is not required at all. The searched value is obviously not in the vector.

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  • Is opening too many datacontexts bad?

    - by ryudice
    I've been checking my application with linq 2 sql profiler, and I noticed that it opens a lot of datacontexts, most of them are opened by the linq datasource I used, since my repositories use only the instance stored in Request.Items, is it bad to open too many datacontext? and how can I make my linqdatasource to use the datacontext that I store in Request.Items for the duration of the request? thanks for any help!

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  • mysql subquery strangely slow

    - by aviv
    I have a query to select from another sub-query select. While the two queries look almost the same the second query (in this sample) runs much slower: SELECT user.id ,user.first_name -- user.* FROM user WHERE user.id IN (SELECT ref_id FROM education WHERE ref_type='user' AND education.institute_id='58' AND education.institute_type='1' ); This query takes 1.2s Explain on this query results: id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY user index first_name 152 141192 Using where; Using index 2 DEPENDENT SUBQUERY education index_subquery ref_type,ref_id,institute_id,institute_type,ref_type_2 ref_id 4 func 1 Using where The second query: SELECT -- user.id -- user.first_name user.* FROM user WHERE user.id IN (SELECT ref_id FROM education WHERE ref_type='user' AND education.institute_id='58' AND education.institute_type='1' ); Takes 45sec to run, with explain: id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY user ALL 141192 Using where 2 DEPENDENT SUBQUERY education index_subquery ref_type,ref_id,institute_id,institute_type,ref_type_2 ref_id 4 func 1 Using where Why is it slower if i query only by index fields? Why both queries scans the full length of the user table? Any ideas how to improve? Thanks.

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  • get next/previous month from a Time object

    - by tcurdt
    I have a Time object and would like to find the next/previous month. Adding subtracting days does not work as the days per month vary. time = Time.parse('21-12-2008 10:51 UTC') next_month = time + 31 * 24 * 60 * 60 Incrementing the month also falls down as one would have to take care of the rolling time = Time.parse('21-12-2008 10:51 UTC') next_month = Time.utc(time.year, time.month+1) time = Time.parse('01-12-2008 10:51 UTC') previous_month = Time.utc(time.year, time.month-1) The only thing I found working was time = Time.parse('21-12-2008 10:51 UTC') d = Date.new(time.year, time.month, time.day) d >>= 1 next_month = Time.utc(d.year, d.month, d.day, time.hour, time.min, time.sec, time.usec) Is there a more elegant way of doing this that I am not seeing? How would you do it?

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  • any faster alternative??

    - by kaushik
    I have to read a file from a particular line number and i know the line number say "n": i have been thinking of two choice: 1)for i in range(n) fname.readline() k=readline() print k 2)i=0 for line in fname: dictionary[i]=line i=i+1 but i want to know faster alternative as i might have to perform this on different files 20000 times. is there is any other better alternatives?? thanking u

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