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• Al Zimmermann's Son of Darts

  - by polygenelubricants

  There's about 2 months left in Al Zimmermann's Son of Darts programming contest, and I'd like to improve my standing (currently in the 60s) to something more respectable. I'd like to get some ideas from the great community of stackoverflow on how best to approach this problem. The contest problem is known as the Global Postage Stamp Problem in literatures. I don't have much experience with optimization algorithms (I know of hillclimbing and simulated annealing in concept only from college), and in fact the program that I have right now is basically sheer brute force, which of course isn't feasible for the larger search spaces. Here are some papers on the subject: A Postage Stamp Problem (Alter & Barnett, 1980) Algorithms for Computing the h-Range of the Postage Stamp Problem (Mossige, 1981) A Postage Stamp Problem (Lunnon, 1986) Two New Techniques for Computing Extremal h-bases Ak (Challis, 1992) Any hints and suggestions are welcome. Also, feel free to direct me to the proper site if stackoverflow isn't it.

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• didSelectRowAtIndexPath TableView Popover Issue

  - by Jack Cody

  I've tried a lot of different code examples including just brute force try this try that but, stumped. The popover left arrow seems to display just fine if the first row is displayed at the very top of the table view but, when the table scrolls down the popover left arrow doesn't align correctly with the table row selected. Solutions or suggestions would be most appreciated. CGRect myFrame = [tableView rectForRowAtIndexPath:indexPath]; [self.editViewPopoverController setPopoverContentSize:CGSizeMake(320, 400)]; [self.editViewPopoverController presentPopoverFromRect:CGRectMake(myFrame.origin.x, myFrame.origin.y + offset, 400, 0) inView:self.view permittedArrowDirections:UIPopoverArrowDirectionLeft animated:YES]; Thanks.

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• How to throttle login attemps in Java webapp?

  - by Jörn Zaefferer

  I want to implement an efficient mechanism to throttle login attemps in my Java web application, to prevent brute-force attacks on user accounts. Jeff explained the why, but not the how. Simon Willison showed an implementation in Python for Django: That doesn't really help me along as I can't use memcached nor Django. Porting his ideas from scratch doesn't seem like a great either - I don't want to reinvent the wheel. I found one Java implementation, though it seems rather naiive: Instead of a LRU cache, it just clears all entries after 15 minutes. EHCache could be an alternative for memcached, but I don't have any experience with it and don't really want to intoduce yet another technology if there are better alternatives for this task. So, whats a good way to implement login throttling in Java?

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• Scheme Depth-first search of a graph function

  - by John Retallack

  This is a homework question,I'm trying to do a Depth-first search function in Scheme,Here's the code I've written so far: (define explore (?(node visited) (let* ([neighbors (force (cdr node))] [next (nextNode visited neighbors)] [is-visited (member? node visited)]) (cond ;if I have no unvisited neighbours print current node and go up one level [(equal? next #f) (begin (display (car node)) (display " "))] ;if current node is not visited and I have unvisited neighbors ;print current node,mark as visited and visit it's neighbors [(and (equal? is-visited #f) (not (equal? next #f))) (begin (display (car node)) (display " ") (explore next (cons node visited)))]) ;go and visit the next neighbor (if (not (equal? (nextNode (cons next visited) neighbors) #f )) (explore (nextNode (cons next visited) neighbors) (cons node visited)))))) 'node' is the current node 'visited' is a list in witch I keep track of the nodes I visited 'nextNode' is a function that returns the first unvisited neighbor if any or #f otherwise 'member?' test's if a node is in the visited list The Graph representation is using adjacent made using references to nodes with letrec so that's why I use force in 'neighbors': Eg: (letrec ([node1 (list "NY" (delay (list node2 node3)))],where node2 and node3 are defined as node1 The problem witch I'm dealing with is that my visited lists looses track of some of the nodes I visited when I come out of recursion,How can I fix this ?

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• Building a directory tree from a list of file paths

  - by Abignale

  I am looking for a time efficient method to parse a list of files into a tree. There can be hundreds of millions of file paths. The brute force solution would be to split each path on occurrence of a directory separator, and traverse the tree adding in directory and file entries by doing string comparisons but this would be exceptionally slow. The input data is usually sorted alphabetically, so the list would be something like: C:\Users\Aaron\AppData\Amarok\Afile C:\Users\Aaron\AppData\Amarok\Afile2 C:\Users\Aaron\AppData\Amarok\Afile3 C:\Users\Aaron\AppData\Blender\alibrary.dll C:\Users\Aaron\AppData\Blender\and_so_on.txt From this ordering my natural reaction is to partition the directory listings into groups... somehow... before doing the slow string comparisons. I'm really not sure. I would appreciate any ideas. Edit: It would be better if this tree were lazy loaded from the top down if possible.

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• Server Security

  - by mahatmanich

  I want to run my own root server (directly accessible from the web without a hardware firewall) with debian lenny, apache2, php5, mysql, postfix MTA, sftp (based on ssh) and maybe dns server. What measures/software would you recomend, and why, to secure this server down and minimalize the attack vector? Webapplications aside ... This is what I have so far: iptables (for gen. packet filtering) fail2ban (brute force attack defense) ssh (chang default, port disable root access) modsecurity - is really clumsy and a pain (any alternative here?) ?Sudo why should I use it? what is the advantage to normal user handling thinking about greensql for mysql www.greensql.net is tripwire worth looking at? snort? What am I missing? What is hot and what is not? Best practices? I like "KISS" - Keep it simple secure, I know it would be nice! Thanks in advance ...

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• Prevent full table scan for query with multiple where clauses

  - by Dave Jarvis

  A while ago I posted a message about optimizing a query in MySQL. I have since ported the data and query to PostgreSQL, but now PostgreSQL has the same problem. The solution in MySQL was to force the optimizer to not optimize using STRAIGHT_JOIN. PostgreSQL offers no such option. Here is the explain: Here is the query: SELECT avg(d.amount) AS amount, y.year FROM station s, station_district sd, year_ref y, month_ref m, daily d LEFT JOIN city c ON c.id = 10663 WHERE -- Find all the stations within a specific unit radius ... -- 6371.009 * SQRT( POW(RADIANS(c.latitude_decimal - s.latitude_decimal), 2) + (COS(RADIANS(c.latitude_decimal + s.latitude_decimal) / 2) * POW(RADIANS(c.longitude_decimal - s.longitude_decimal), 2)) ) <= 50 AND -- Ignore stations outside the given elevations -- s.elevation BETWEEN 0 AND 2000 AND sd.id = s.station_district_id AND -- Gather all known years for that station ... -- y.station_district_id = sd.id AND -- The data before 1900 is shaky; insufficient after 2009. -- y.year BETWEEN 1980 AND 2000 AND -- Filtered by all known months ... -- m.year_ref_id = y.id AND m.month = 12 AND -- Whittled down by category ... -- m.category_id = '001' AND -- Into the valid daily climate data. -- m.id = d.month_ref_id AND d.daily_flag_id <> 'M' GROUP BY y.year It appears as though PostgreSQL is looking at the DAILY table first, which is simply not the right way to go about this query as there are nearly 300 million rows. How do I force PostgreSQL to start at the CITY table? Thank you!

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• Multi-column sorting with an NSTableView bound to an NSArrayController

  - by Cinder6

  Hi there. I have an NSTableView that's bound to an NSArrayController. Everything gets loaded into the table correctly, and I have sort keys and selectors set for the various columns (this also works). What I'm trying to do is sort multiple columns when the user clicks one column header, but I can't find any way to do this. I could brute-force a way by overriding tableView:mouseDownInHeaderOfTableColumn:, but that seems an inelegant way of doing it. Is there a good way of doing multi-column sorting in an NSTableView using bindings?

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• RAR password recovery on GPU using ATI Stream processor

  - by Wajdy Essam

  Hello, I'm newbie in GPU programming , and i work on brute force RAR Password Recovery on ATI Stream Processor using brook+ language, but i see that the kernel written in brook+ language doesn't allow any calling to normal functions (except kernel functions) , my questions is : 1) how to use unrar.dll (to unrar archive files) API in this situation? and is this the only way to program RAR password recovery? 2) what about crack and ElcomSoft software that use GPU , how they work ? 3) what exactly the role for the function work inside GPU (ATI Stream processor or CUDA) in this program? 4) is nVidia/CUDA technology is easier/more flexible than ATI/brook+ language ?

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• Best Fit Scheduling Algorithm

  - by Teegijee

  I'm writing a scheduling program with a difficult programming problem. There are several events, each with multiple meeting times. I need to find an arrangement of meeting times such that each schedule contains any given event exactly once, using one of each event's multiple meeting times. Obviously I could use brute force, but that's rarely the best solution. I'm guessing this is a relatively basic computer science problem, which I'll learn about once I am able to start taking computer science classes. In the meantime, I'd prefer any links where I could read up on this, or even just a name I could Google.

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• Looking for ideas how to refactor my (complex) algorithm

  - by _simon_

  I am trying to write my own Game of Life, with my own set of rules. First 'concept', which I would like to apply, is socialization (which basicaly means if the cell wants to be alone or in a group with other cells). Data structure is 2-dimensional array (for now). In order to be able to move a cell to/away from a group of another cells, I need to determine where to move it. The idea is, that I evaluate all the cells in the area (neighbours) and get a vector, which tells me where to move the cell. Size of the vector is 0 or 1 (don't move or move) and the angle is array of directions (up, down, right, left). This is a image with representation of forces to a cell, like I imagined it (but reach could be more than 5): Let's for example take this picture: Forces from lower left neighbour: down (0), up (2), right (2), left (0) Forces from right neighbour : down (0), up (0), right (0), left (2) sum : down (0), up (2), right (0), left (0) So the cell should go up. I could write an algorithm with a lot of if statements and check all cells in the neighbourhood. Of course this algorithm would be easiest if the 'reach' parameter is set to 1 (first column on picture 1). But what if I change reach parameter to 10 for example? I would need to write an algorithm for each 'reach' parameter in advance... How can I avoid this (notice, that the force is growing potentialy (1, 2, 4, 8, 16, 32,...))? Can I use specific design pattern for this problem? Also: the most important thing is not speed, but to be able to extend initial logic. Things to take into consideration: reach should be passed as a parameter i would like to change function, which calculates force (potential, fibonacci) a cell can go to a new place only if this new place is not populated watch for corners (you can't evaluate right and top neighbours in top-right corner for example)

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• Objective-C object release and allocation timing

  - by ryanjm.mp

  The code for this question is too long to be of any use. But I'm pretty sure my problem has to do with releasing a class. I have a helper class, ConnectionHelper.h/.m, that handles a NSURLConnection for me. Basically, I give it the URL I want and it returns the data (it happens to do a quick json parse on it too). It has a delegate which I set to the calling class (in this case: DownloadViewController). When it finishes the download, it calls [delegate didFinishParseOf:objectName withDictionary:dictionary];. Then in DownloadViewController I release ConnectionHelper and alloc a new one in order to download the next object. My problem is, I do this once, and then it creates the connection for the second one, and then my program just crashes. After this call: [[NSHTTPCookieStorage sharedHTTPCookieStorage] setCookieAcceptPolicy:NSHTTPCookieAcceptPolicyNever]; NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self]; Then I don't think any of the following methods are called: - (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error - (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge So am I right in that I'm not releasing something? When I release it the first time, the dealloc function isn't being called. Is there a way I can "force" it to deallocate? Do I need to force it to? I didn't think it would matter since I allocating a new ConnectionHelper for the new call. How else would they overlap / conflict with each other? Thank you.

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• Fastest way to do mass update

  - by user356004

  Let’s say you have a table with about 5 million records and a nvarchar(max) column populated with large text data. You want to set this column to NULL if SomeOtherColumn = 1 in fastest possible way. The brute force UPDATE does not work very well here because it will create large implicit transaction and take forever. Doing updates in small batches of 50K records at a time works but it’s still taking 47 hrs to complete on beefy 32 core/64GB server. Is there any way to do this update faster? Are there any magic query hints/table options that scarifies something else (like concurrency) in exchange of speed? NOTE: Creating temp table or temp column is not an option because this nvarchar(max) column involves lots of data and so consumes lots of space!

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• Distributing points over a surface within boundries

  - by vise

  I'm interested in a way (algorithm) of distributing a predefined number of points over a 4 sided surface like a square. The main issue is that each point has got to have a minimum and maximum proximity to each other (random between two predefined values). Basically the distance of any two points should not be closer than let's say 2, and a further than 3. My code will be implemented in ruby (the points are locations, the surface is a map), but any ideas or snippets are definitely welcomed as all my ideas include a fair amount of brute force.

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• Perl OO frameworks and program design - Moose and Conway's inside-out objects (Class::Std)

  - by Emmel

  This is more of a use-case type of question... but also generic enough to be more broadly applicable: In short, I'm working on a module that's more or less a command-line wrapper; OO naturally. Without going into too many details (unless someone wants them), there isn't a crazy amount of complexity to the system, but it did feel natural to have three or four objects in this framework. Finally, it's an open source thing I'll put out there, rather than a module with a few developers in the same firm working on it. First I implemented the OO using Class::Std, because Perl Best Practices (Conway, 2005) made a good argument for why to use inside-out objects. Full control over what attributes get accessed and so on, proper encapsulation, etc. Also his design is surprisingly simple and clever. I liked it, but then noticed that no one really uses this; in fact it seems Conway himself doesn't really recommend this anymore? So I moved to everyone's favorite, Moose. It's easy to use, although way way overkill feature-wise for what I want to do. The big, major downside is: it's got a slew of module dependencies that force users of my module to download them all. A minor downside is it's got way more functionality than I really need. What are recommendations? Inconvenience fellow developers by forcing them to use a possibly-obsolete module, or force every user of the module to download Moose and all its dependencies? Is there a third option for a proper Perl OO framework that's popular but neither of these two?

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• In R, when using named rows, can a sparse matrix column be added to another sparse matrix?

  - by ayman

  I have two sparse matrices, m1 and m2: > m1 <- Matrix(data=0,nrow=2, ncol=1, sparse=TRUE, dimnames=list(c("b","d"),NULL)) > m2 <- Matrix(data=0,nrow=2, ncol=1, sparse=TRUE, dimnames=list(c("a","b"),NULL)) > m1["b",1]<- 4 > m2["a",1]<- 5 > m1 2 x 1 sparse Matrix of class "dgCMatrix" b 4 d . > m2 2 x 1 sparse Matrix of class "dgCMatrix" a 5 b . > and I want to cbind() them to make a sparse matrix like: [,1] [,2] a . 5 b 4 . d . . however cbind() ignores the named rows: > cbind(m1[,1],m2[,1]) [,1] [,2] b 4 5 d 0 0 is there some way to do this without a brute force loop?

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• Changing the colour of \textbullet in LaTeX Beamer

  - by Seamus

  I don't want to use Beamer's standard blue colour theme. I want to use beaver, which is deep reds. Everything looks nice, except that if I use itemize the bullet points are still blue. Is there a nice way to have the bullets vary with what colour theme I was using? (If I were to opt for a yellowish colour theme, I'd expect the bullets to go yellow too.) If there isn't, what is the brute force way to change the bullet points red? Or at the very least, make them go back to black again.

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• php selecting hash using wildcards

  - by tipu

  Say I have a hashmap, $hash = array('fox' => 'some value', 'fort' => 'some value 2', 'fork' => 'some value again); I am trying to accomplish an autocomplete feature. When the user types 'fo', I would like to retrieve, via ajax, the 3 keys from $hash. When the user types 'for', I would like to only retrieve the keys fort and fork. Is this possible? What I was thinking was using binary search to isolate the keys with 'f', instead of brute-force searching. Then continue eliminating the indexes as the user types out their query. Is there a more efficient solution to this?

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• Codeigniter: Make field increase by 1 up to a number?

  - by Kevin Brown

  In my validation class I have this: $fields['a_1'] = 'First Question'; $fields['a_2'] = 'Second Question'; $fields['a_3'] = 'Third Question'; $fields['a_4'] = 'Fourth Question'; This is getting old--I have about 40 of these to write, and each set has matching validation rules: $rules['a_1'] = 'hour'; $rules['a_2'] = 'hour'; ... Is there a way to say: $fields['a_' . 1 - 17] = "One, Two" Etc... Just curious... if not, I'll brute force it.

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• can't properly shutdown ubuntu and sound problem on HP mini 311 netbook

  - by Viele

  hi, I recently bought a HP mini 311 netbook. I replaced its harddrive and installed ubuntu 10.04. Since then, I have encountered some very strange problem with its sound and shutdown/reboot. At times, when I start the computer, it will have no sound, on the GUI the sound is at max, but no sound is available. This sometimes also happen after after upgrades, hibernate, and toggling the wireless radio button. Strangely, when the sound is out the device will also refuse to be shutdown. If I shutdown the computer using the GUI, it will simply go back to the log in screen without actually shutting down. If I use "sudo shutdown 0", the computer will hang on the loading screen of the shut down process. I had to force the pc to shutdown by holding the power button down. usually (probably always) after I force a turn-off then start off again. the sound and shutdown become normal. I wonder if anyone have clues regarding to the cause of this problem. This the info about the computer: 1) installed ubuntu 10.04LTS RC, later upgraded to formal released version. 2) cat /proc/asound/version == "Advanced Linux Sound Architecture Driver Version 1.0.21." however, when doing 'alsaconf' the version displayed is 1.0.23 any help is appreciated. Thanks

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• Better to build or buy a compute grid platform?

  - by James B

  I am looking to do some quite processor-intensive brute force processing for string matching. I have run my prototype in a multi-threaded environment and compared the performance to an implementation using Gridgain with a couple of nodes (also multithreaded). The performance I observed was that my Gridgain implementation performed slower to my multithreaded implementation. It could be the case that there was a flaw in my gridgain implementation, but it was only a prototype, and I thought the results were indicative. So my question is this: What are the advantages of having to learn and then build an implementation for a particular grid platform (hadoop, gridgain, or EC2 if going hosted - other suggestions welcome), when one could fairly easily put together a lightweight compute grid platform with a much shallower learning curve?...i.e. what do we get for free with these cloud/grid platforms that are worth having/tricky to implement? (Please note, I don't have any need for a data grid) Cheers, -James (p.s. Happy to make this community wiki if needbe)

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• Content-disposition:inline header won't show images inline?

  - by hamstar

  I'm trying to show an image inline on a page. It is being served by a codeigniter controller. class Asset extends MY_Controller { function index( $folder, $file ) { $asset = "assets/$folder/$file"; if ( !file_exists( $asset ) ) { show_404(); return; } switch ( $folder ) { case 'css': header('Content-type: text/css'); break; case 'js': header('Content-type: text/javascript'); break; case 'images': $ext = substr( $file, strrpos($file, '.') ); switch ( $ext ) { case 'jpg': $ext = 'jpeg'; break; case 'svg': $ext = 'svg+xml'; break; } header('Content-Disposition: inline'); header('Content-type: image/'.$ext); } readfile( $asset ); } } When I load a image in Chrome of FF its pops up the download window. I know when the browser can't display the content inline it will force a download anyway, but these are PNG and GIF images which display in the browser fine otherwise. In IE it doesn't force a download but it displays the image in ASCII. If I comment out the entire image case it FF and Chrome both display the ASCII but not the image. I thought setting the content type would allow FF and Chrome to show the actual image, and also allow the location to be used as an src. The javascript and css shows fine of course. Anyone got any ideas how I can make the images show properly? Thanks :)

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• Rails: unable to set any attribute of child model

  - by Bryan Roth

  I'm having a problem instantiating a ListItem object with specified attributes. For some reason all attributes are set to nil even if I specify values. However, if I specify attributes for a List, they retain their values. Attributes for a List retain their values: >> list = List.new(:id => 20, :name => "Test List") => #<List id: 20, name: "Test List"> Attributes for a ListItem don't retain their values: >> list_item = ListItem.new(:id => 17, :list_id => 20, :name => "Test Item") => #<ListItem id: nil, list_id: nil, name: nil> UPDATE #1: I thought the id was the only attribute not retaining its value but realized that setting any attribute for a ListItem gets set to nil. list.rb: class List < ActiveRecord::Base has_many :list_items, :dependent => :destroy accepts_nested_attributes_for :list_items, :reject_if => lambda { |a| a[:name].blank? }, :allow_destroy => true end list_item.rb: class ListItem < ActiveRecord::Base belongs_to :list validates_presence_of :name end schema.rb ActiveRecord::Schema.define(:version => 20100506144717) do create_table "list_items", :force => true do |t| t.integer "list_id" t.string "name" t.datetime "created_at" t.datetime "updated_at" end create_table "lists", :force => true do |t| t.string "name" t.datetime "created_at" t.datetime "updated_at" end end

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• Why is Java not telling me when I can't use Integer?

  - by Sebi

  For a small project (Problem 10 Project Euler) i tried to sum up all prime numbers below 2 millions. So I used a brute force method and iterated from 0 to 2'000'000 and checked if the number is a prime. If it is I added it to the sum: private int sum = 0; private void calculate() { for (int i = 0; i < 2000000; i++) { if (i.isPrime()) { sum = sum + i; } } sysout(sum) } The result of this calculation is 1179908154, but this is incorrect. So i changed int to BigInteger and now i get the correct sum 142913828922. Obviously the range of int was overflowed. But why can't Java tell my that? (e.g. by an exception)

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• How do find the longest path in a cyclic Graph between two nodes?

  - by Nazgulled

  Hi, I already solved most the questions posted here, all but the longest path one. I've read the Wikipedia article about longest paths and it seems any easy problem if the graph was acyclic, which mine is not. How do I solve the problem then? Brute force, by checking all possible paths? How do I even begin to do that? I know it's going to take A LOT on a Graph with ~18000. But I just want to develop it anyway, cause it's required for the project and I'll just test it and show it to the instructor on a smaller scale graph where the execution time is just a second or two. At least I did all tasks required and I have a running proof of concept that it works but there's no better way on cyclic graphs. But I don't have clue where to start checking all these paths...

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