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  • Socket stops communicating

    - by user1392992
    I'm running python 2.7 code on a Raspberry Pi that receives serial data from an Arduino, processes it, and sends it to a Windows box over a wifi link. The Pi is wired to a Linksys router running in client bridge mode and that router connects over wifi to another Linksys router to which the Windows box is wired. The code in the Pi runs fine for some (apparently) random interval, and then the Pi becomes unreachable from the Windows box. I'm running PUTTY on the the Windows machine to connect to the Pi and when the fail occurs I get a message saying there's been a network error and the Pi is not reachable. Pinging the Pi from the Windows machine works fine until the error, at which time it produces "Reply from 192.168.0.129: Destination host unreachable." The client bridge router to which the Pi is connected remains reachable. I've got the networking code on the Pi wrapped in an exception handler, and when it fails it shows the following: Ethernet problem: Traceback (most recent call last): File "garage.py", line 108, in module s.connect((host, port)) File "/usr/lib/python2.7/socket.py", line 224, in meth return getattr(self._sock,name)(*args) error: [Errno 113] No route to host None The relevant python code looks like: import socket import traceback host = '192.168.0.129' port = 31415 in the setup, and after serial data has been processed: try: bline = strline.encode('utf-8') s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((host, port)) s.send(bline) s.close() except: print "Ethernet problem: " print traceback.print_exc() Where strline contains the processed data. As I said, this runs fine for a few hours more or less before failing. Any ideas? EDIT: When PUTTY fails its error message is :Network Error: Software caused connection abort."

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  • Debug.Assert-s use the same error message. Should I promote it to a static variable?

    - by Hamish Grubijan
    I love Asserts and code readability but not code duplication, and in several places I use a Debug.Assert which checks for the same condition like so: Debug.Assert(kosherBaconList.SelectedIndex != -1, "An error message along the lines - you should not ever be able to click on edit button without selecting a kosher bacon first."); This is in response to an actual bug, although the actual list does not contain kosher bacon. Anyhow, I can think of two approaches: private static readonly mustSelectKosherBaconBeforeEditAssertMessage = "An error message along the lines - you should not ever be able to " + "click on edit button without selecting a something first."; ... Debug.Assert( kosherBaconList.SelectedIndex != -1, mustSelectKosherBaconBeforeEditAssertMessage) or: if (kosherBaconList.SelectedIndex == -1) { AssertMustSelectKosherBaconBeforeEdit(); } ... [Conditional("DEBUG")] private void AssertMustSelectKosherBaconBeforeEdit() { // Compiler will optimize away this variable. string errorMessage = "An error message along the lines - you should not ever be able to " + "click on edit button without selecting a something first."; Debug.Assert(false, errorMessage); } or is there a third way which sucks less than either one above? Please share. General helpful relevant tips are also welcome.

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  • Any techniques to interrupt, kill, or otherwise unwind (releasing synchronization locks) a single de

    - by gojomo
    I have a long-running process where, due to a bug, a trivial/expendable thread is deadlocked with a thread which I would like to continue, so that it can perform some final reporting that would be hard to reproduce in another way. Of course, fixing the bug for future runs is the proper ultimate resolution. Of course, any such forced interrupt/kill/stop of any thread is inherently unsafe and likely to cause other unpredictable inconsistencies. (I'm familiar with all the standard warnings and the reasons for them.) But still, since the only alternative is to kill the JVM process and go through a more lengthy procedure which would result in a less-complete final report, messy/deprecated/dangerous/risky/one-time techniques are exactly what I'd like to try. The JVM is Sun's 1.6.0_16 64-bit on Ubuntu, and the expendable thread is waiting-to-lock an object monitor. Can an OS signal directed to an exact thread create an InterruptedException in the expendable thread? Could attaching with gdb, and directly tampering with JVM data or calling JVM procedures allow a forced-release of the object monitor held by the expendable thread? Would a Thread.interrupt() from another thread generate a InterruptedException from the waiting-to-lock frame? (With some effort, I can inject an arbitrary beanshell script into the running system.) Can the deprecated Thread.stop() be sent via JMX or any other remote-injection method? Any ideas appreciated, the more 'dangerous', the better! And, if your suggestion has worked in personal experience in a similar situation, the best!

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  • Does this copy the reference or the object?

    - by Water Cooler v2
    Sorry, I am being both thick and lazy, but mostly lazy. Actually, not even that. I am trying to save time so I can do more in less time as there's a lot to be done. Does this copy the reference or the actual object data? public class Foo { private NameValueCollection _nvc = null; public Foo( NameValueCollection nvc) { _nvc = nvc; } } public class Bar { public static void Main() { NameValueCollection toPass = new NameValueCollection(); new Foo( toPass ); // I believe this only copies the reference // so if I ever wanted to compare toPass and // Foo._nvc (assuming I got hold of the private // field using reflection), I would only have to // compare the references and wouldn't have to compare // each string (deep copy compare), right? } I think I know the answer for sure: it only copies the reference. But I am not even sure why I am asking this. I guess my only concern is, if, after instantiating Foo by calling its parameterized ctor with toPass, if I needed to make sure that the NVC I passed as toPass and the NVC private field _nvc had the exact same content, I would just need to compare their references, right?

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  • 32-bit JVM on 64-bit Windows crashes on launch with -Xmx1300m and plenty of free memory

    - by Konrad Garus
    I'm struggling with Java heap space settings. The default Java on Windows is the 32-bit client regardless of OS version (that's what Oracle recommends to all users). It appears to set max heap size to 256 MB by default, and that is too little for me. I use a custom launcher to start the application. I would like it to use more memory on computers with plenty RAM, and default to -Xmx512m on those with less RAM. As far as I'm aware, the only way is the static -Xmx setting (that has to be set on launch). I have a user who has 8 GB RAM, 64-bit Windows and 32-bit Java 7. Maximum memory visible to the JVM is 4G (as returned by querying OperatingSystemMXBean). I understand why, no issue. For some reason my application is unable to start for this user with -Xmx1300m, even though he has 2.3G free memory. He closed some applications (having 5G free memory), and still it would not launch. The error reported to me was: error occured during init of vm could not reserve enough space for object heap What's going on? Could it be that the 32-bit JVM is only able to address the "first" 4G of memory and has to have a 1300M block available within those first 4 gigabytes? How can I solve this problem, except for asking everyone to install 64-bit Java (what is unlikely to be acceptable)?

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  • Point covering problem

    - by Sean
    I recently had this problem on a test: given a set of points m (all on the x-axis) and a set n of lines with endpoints [l, r] (again on the x-axis), find the minimum subset of n such that all points are covered by a line. Prove that your solution always finds the minimum subset. The algorithm I wrote for it was something to the effect of: (say lines are stored as arrays with the left endpoint in position 0 and the right in position 1) algorithm coverPoints(set[] m, set[][] n): chosenLines = [] while m is not empty: minX = min(m) bestLine = n[0] for i=1 to length of n: if n[i][0] <= m and n[i][1] > bestLine[1] then bestLine = n[i] add bestLine to chosenLines for i=0 to length of m: if m <= bestLine[1] then delete m[i] from m return chosenLines I'm just not sure if this always finds the minimum solution. It's a simple greedy algorithm so my gut tells me it won't, but one of my friends who is much better than me at this says that for this problem a greedy algorithm like this always finds the minimal solution. For proving mine always finds the minimal solution I did a very hand wavy proof by contradiction where I made an assumption that probably isn't true at all. I forget exactly what I did. If this isn't a minimal solution, is there a way to do it in less than something like O(n!) time? Thanks

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  • How often should network traffic/collisions cause SNMP Sets to fail?

    - by A. Levy
    My team has a situation where an SNMP SET will fail once every two weeks or so. Since this set happens automatically, we don't necessarily notice it immediately when it fails, and this can result in an inconsistent configuration and associated wailing and gnashing of teeth. The plan is to fix this by having our software automatically retry the SET when it fails. The problem is, we aren't sure why the failure is happening. My (extremely limited) knowledge of SNMP isn't particularly helpful in diagnosing this problem, so I thought I'd ask StackOverflow for some advice. We think that every so often a spike in network traffic will cause the SET to fail. Since SNMP uses UDP for communication, I would think it would be relatively easy for a command to be drowned out if traffic was high for a short period of time. However, I have no idea how common this is. We have a small network with a single cisco router and there are less than a dozen SNMP controlled devices on that network. In addition to the SNMP traffic, there are some status web pages being loaded from the various devices. In case it makes a difference, I believe we are using the AdventNet SNMP API version 4.0.4 for Java. Does it sound reasonable that there will be some SET commands dropped occasionally, or should we be looking for other causes?

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  • C# Application process hangs after some time

    - by Chris
    Hi, I implemented a simple C# application which inserts about 350000 records into the database. This used to work well and the process took approximately 20 minutes. I created a progress bar which lets you know approximately the progress of the records insertion. When the progress bar reaches about 75% it stops progressing. I have to manually terminate the program as the process doesn't seem to complete. If I use less data (like 10000), the progress bar finishes and the process is completed. However when I try to insert all the records, this won't happen any more. Note that if I wait longer to terminate the program manually, more records would have been inserted. For example, if I terminate the program after 15 minutes, 200000 records are inserted, whereas if I terminate the program after 20 minutes, 250000 records are inserted. This program is using a single thread. In face I can't do anything else until the process is complete. Does this have anything to do with threading or processes? Any feedback will be greatly appreciated. Thanks.

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  • PHP & form validation

    - by user887515
    I have a form that I'm submitting via ajax, and I want to return a message of the list of fields that were empty. I've got that all done and dusted, but it just seems really long winded on the PHP side of things. How can I do the below in a less convoluted way? <?php if(empty($_POST["emailaddress"])){ $error = 'true'; $validation_msg = 'Country missing.'; if(empty($error_msg)){ $error_msg .= $validation_msg; } else{ $error_msg .= '\n' . $validation_msg; } } if(empty($_POST["password"])){ $error = 'true'; $validation_msg = 'Country missing.'; if(empty($error_msg)){ $error_msg .= $validation_msg; } else{ $error_msg .= '\n' . $validation_msg; } } if(empty($_POST["firstname"])){ $error = 'true'; $validation_msg = 'First name missing.'; if(empty($error_msg)){ $error_msg .= $validation_msg; } else{ $error_msg .= '\n' . $validation_msg; } } if(empty($_POST["lastname"])){ $error = 'true'; $validation_msg = 'Last name missing.'; if(empty($error_msg)){ $error_msg .= $validation_msg; } else{ $error_msg .= '\n' . $validation_msg; } } if($error){ header('HTTP/1.1 500 Internal Server Error'); header('Content-Type: application/json'); die($error_msg); } ?>

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  • subset complete or balance dataset in r

    - by SHRram
    I have a dataset that unequal number of repetition. I want to subset a data by removing those entries that are incomplete (i.e. replication less than maximum). Just small example: set.seed(123) mydt <- data.frame (name= rep ( c("A", "B", "C", "D", "E"), c(1,2,4,4, 3)), var1 = rnorm (14, 3,1), var2 = rnorm (14, 4,1)) mydt name var1 var2 1 A 2.439524 3.444159 2 B 2.769823 5.786913 3 B 4.558708 4.497850 4 C 3.070508 2.033383 5 C 3.129288 4.701356 6 C 4.715065 3.527209 7 C 3.460916 2.932176 8 D 1.734939 3.782025 9 D 2.313147 2.973996 10 D 2.554338 3.271109 11 D 4.224082 3.374961 12 E 3.359814 2.313307 13 E 3.400771 4.837787 14 E 3.110683 4.153373 summary(mydt) name var1 var2 A:1 Min. :1.735 Min. :2.033 B:2 1st Qu.:2.608 1st Qu.:3.048 C:4 Median :3.120 Median :3.486 D:4 Mean :3.203 Mean :3.688 E:3 3rd Qu.:3.446 3rd Qu.:4.412 Max. :4.715 Max. :5.787 I want to get rid of A, B, E from the data as they are incomplete. Thus expected output: name var1 var2 4 C 3.070508 2.033383 5 C 3.129288 4.701356 6 C 4.715065 3.527209 7 C 3.460916 2.932176 8 D 1.734939 3.782025 9 D 2.313147 2.973996 10 D 2.554338 3.271109 11 D 4.224082 3.374961 Please note the dataset is big, the following may not a option: mydt[mydt$name == "C",] mydt[mydt$name == "D", ]

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  • "end()" iterator for back inserters?

    - by Thanatos
    For iterators such as those returned from std::back_inserter(), is there something that can be used as an "end" iterator? This seems a little nonsensical at first, but I have an API which is: template<typename InputIterator, typename OutputIterator> void foo( InputIterator input_begin, InputIterator input_end, OutputIterator output_begin, OutputIterator output_end ); foo performs some operation on the input sequence, generating an output sequence. (Who's length is known to foo but may or may not be equal to the input sequence's length.) The taking of the output_end parameter is the odd part: std::copy doesn't do this, for example, and assumes you're not going to pass it garbage. foo does it to provide range checking: if you pass a range too small, it throws an exception, in the name of defensive programming. (Instead of potentially overwriting random bits in memory.) Now, say I want to pass foo a back inserter, specifically one from a std::vector which has no limit outside of memory constraints. I still need a "end" iterator - in this case, something that will never compare equal. (Or, if I had a std::vector but with a restriction on length, perhaps it might sometimes compare equal?) How do I go about doing this? I do have the ability to change foo's API - is it better to not check the range, and instead provide an alternate means to get the required output range? (Which would be needed anyways for raw arrays, but not required for back inserters into a vector.) This would seem less robust, but I'm struggling to make the "robust" (above) work.

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  • C# : How to round-off hours based on Minutes(hours+0 if min<30, hours+1 otherwise) ?

    - by infant programmer
    I need to round-off the hours based on the minutes in a dateTime variable. The condition is : if minutes are less than 30, then minutes must be set to zero and no changes to hours, Else if minutes =30, then hours must be set to hours+1 and minutes are again set to zero. Seconds are ignored. example: 11/08/2008 04:30:49 should become 11/08/2008 05:00:00 and 11/08/2008 04:29:49 should become 11/08/2008 04:00:00 I have written a Code which works perfectly fine, but just wanted to know a better method if could be written and also would appreciate alternative method(s). string date1 = "11/08/2008 04:30:49"; DateTime startTime; DateTime.TryParseExact(date1, "MM/dd/yyyy HH:mm:ss", null, System.Globalization.DateTimeStyles.None, out startTime); if (Convert.ToInt32((startTime.Minute.ToString())) > 29) { startTime = DateTime.Parse(string.Format("{0}/{1}/{2} {3}:{4}:{5}", startTime.Month.ToString(), startTime.Day.ToString(), startTime.Year.ToString(), startTime.Hour.ToString(), "00", "00")); startTime = startTime.Add(TimeSpan.Parse("01:00:00")); Console.WriteLine("startTime is :: {0}", startTime.ToString("MM/dd/yyyy HH:mm:ss")); } else { startTime = DateTime.Parse(string.Format("{0}/{1}/{2} {3}:{4}:{5}", startTime.Month.ToString(), startTime.Day.ToString(), startTime.Year.ToString(), startTime.Hour.ToString(), "00", "00")); Console.WriteLine("startTime is :: {0}", startTime.ToString("MM/dd/yyyy HH:mm:ss")); }

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  • ASP.NET MVC3 ValueProvider drops string input to a double property

    - by Daniel Koverman
    I'm attempting to validate the input of a text box which corresponds to a property of type double in my model. If the user inputs "foo" I want to know about it so I can display an error. However, the ValueProvider is dropping the value silently (no errors are added to the ModelState). In a normal submission, I fill in "2" for the text box corresponding to myDouble and submit the form. Inspecting controllerContext.HttpContext.Request.Form shows that myDouble=2, among other correct inputs. bindingContext.ValueProvider.GetValue("myDouble") == 2, as expected. The bindingContext.ModelState.Count == 6 and bindingContext.ModelState["myDouble"].Errors.Count == 0. Everything is good and the model binds as expected. Then I fill in "foo" for the text box corresponding to myDouble and submitted the form. Inspecting controllerContext.HttpContext.Request.Form shows that myDouble=foo, which is what I expected. However, bindingContext.ValueProvider.GetValue("myDouble") == null and bindingContext.ModelState.Count == 5 (The exact number isn't important, but it's one less than before). Looking at the ValueProvider, is as if myDouble was never submitted and the model binding occurs as if it wasn't. This makes it difficult to differentiate between a bad input and no input. Is this the expected behavior of ValueProvider? Is there a way to get ValueProvider to report when conversion fails without implementing a custom ValueProvider? Thanks!

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  • Fixing an SQL where statement that is ugly and confusing

    - by Mike Wills
    I am directly querying the back-end MS SQL Server for a software package. The key field (vehicle number) is defined as alpha though we are entering numeric value in the field. There is only one exception to this, we place an "R" before the number when the vehicle is being retired (which means we sold it or the vehicle is junked). Assuming the users do this right, we should not run into a problem using this method. (Right or wrong isn't the issue here) Fast forward to now. I am trying to query a subset of these vehicle numbers (800 - 899) for some special processing. By doing a range of '800' to '899' we also get 80, 81, etc. If I cast the vehicle number into an INT, I should be able to get the right range. Except that these "R" vehicles are kicking me in the butt now. I have tried where vehicleId not like 'R%' and cast(vehicleId as int) between 800 and 899 however, I get a casting error on one of these "R" vehicles. What does work is where vehicleId not between '800' and '899' and cast(vehicleId as int) between 800 and 899', but I feel there has to be a better way and less confusing way. I have also tried other variations with HAVING and a sub-query all producing a casting error.

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  • Jquery Mobile is adding text above my "<input type=submit"> automatically, how do i prevent this?

    - by Jack Dalton
    I've just begin work on a mobile version for one of my sites. I've set up my sign up form for my users. It worked fine and the CSS styled it correctly. @using (Html.BeginForm("XXX", "Registration", FormMethod.Post, new { @class = "twitter-sign-in-container" })) { <input type="submit" name="twitter-button" value="Sign in with Twitter" id="twitter-button" /> } Once I added Jquery mobile to the project if found that random unstyled text started to show up. On inspection I found that all input submits where being wrapped in new tags and adding un tagged text == to the inputs "Value": <form action="/registration/xxx" class="twitter-sign-in-container" method="post"> <div class="ui-btn ui-input-btn ui-corner-all ui-shadow"> "Sign in with Twitter" <input type="submit" name="twitter-button" value="Sign in with Twitter" id="twitter-button"> </div> </form> Does anyone have any clue as to why the "sign up with twitter" text is being added, and how i stop it? P.S Less important but I'd also like to know why Jquery wraps form contents in the bellow div.

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  • Design for fastest page download

    - by mexxican
    I have a file with millions of URLs/IPs and have to write a program to download the pages really fast. The connection rate should be at least 6000/s and file download speed at least 2000 with avg. 15kb file size. The network bandwidth is 1 Gbps. My approach so far has been: Creating 600 socket threads with each having 60 sockets and using WSAEventSelect to wait for data to read. As soon as a file download is complete, add that memory address(of the downloaded file) to a pipeline( a simple vector ) and fire another request. When the total download is more than 50Mb among all socket threads, write all the files downloaded to the disk and free the memory. So far, this approach has been not very successful with the rate at which I could hit not shooting beyond 2900 connections/s and downloaded data rate even less. Can somebody suggest an alternative approach which could give me better stats. Also I am working windows server 2008 machine with 8 Gig of memory. Also, do we need to hack the kernel so as we could use more threads and memory. Currently I can create a max. of 1500 threads and memory usage not going beyond 2 gigs [ which technically should be much more as this is a 64-bit machine ]. And IOCP is out of question as I have no experience in that so far and have to fix this application today. Thanks Guys!

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  • Help me sort programing languages a bit

    - by b-gen-jack-o-neill
    Hi, so I asked here few days ago about C# and its principles. Now, if I may, I have some additional general questions about some languages, becouse for novice like me, it seems a bit confusing. To be exact I want to ask more about language functions capabilities than syntax and so. To be honest, its just these special functions that bothers me and make me so confused. For exmaple, C has its printf(), Pascal has writeln() and so. I know in basic the output in assembler of these funtions would be similiar, every language has more or less its special functions. For console output, for file manipulation, etc. But all these functions are de-facto part of its OS API, so why is for example in C distinguished between C standard library functions and (on Windows) WinAPI functions when even printf() has to use some Windows feature, call some of its function to actually show desired text on console window, becouse the actuall "showing" is done by OS. Where is the line between language functions and system API? Now languages I dont quite understand - Python, Ruby and similiar. To be more specific, I know they are similiar to java and C# in term they are compiled into bytecode. But, I do not unerstand what are its capabilities in term of building GUI applications. I saw tutorial for using Ruby to program GUI applications on Linux and Windows. But isn´t that just some kind of upgrade? I mean fram other tutorials It seemed like these languages was first intended for small scripts than building big applications. I hope you understand why I am confused. If you do, please help me sort it out a bit, I have no one to ask.

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  • C++ private inheritance and static members/types

    - by WearyMonkey
    I am trying to stop a class from being able to convert its 'this' pointer into a pointer of one of its interfaces. I do this by using private inheritance via a middle proxy class. The problem is that I find private inheritance makes all public static members and types of the base class inaccessible to all classes under the inheriting class in the hierarchy. class Base { public: enum Enum { value }; }; class Middle : private Base { }; class Child : public Middle { public: void Method() { Base::Enum e = Base::value; // doesn't compile BAD! Base* base = this; // doesn't compile GOOD! } }; I've tried this in both VS2008 (the required version) and VS2010, neither work. Can anyone think of a workaround? Or a different approach to stopping the conversion? Also I am curios of the behavior, is it just a side effect of the compiler implementation, or is it by design? If by design, then why? I always thought of private inheritance to mean that nobody knows Middle inherits from Base. However, the exhibited behavior implies private inheritance means a lot more than that, in-fact Child has less access to Base than any namespace not in the class hierarchy!

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  • Efficiently get the size of a parameter pack up to a certain index

    - by NmdMystery
    I want to be able to determine the number of bytes that are in a subset of a parameter pack from 0 to a given index. Right now I'm using a non-constexpr way of doing this. Below is my code: template <size_t index, typename... args> struct pack_size_index; template <size_t index, typename type_t, typename... args> struct pack_size_index <index, type_t, args...> { static const size_t index_v = index; static const size_t value(void) { if (index_v > 0) { return sizeof(type_t) + pack_size_index<index - 1, args...>::value(); } return 0; } }; template <size_t index> struct pack_size_index <index> { static const size_t index_v = index; static const size_t value(void) { return 0; } }; Usage: //output: 5 (equal to 1 + 4) std::cout << pack_size_index<2, bool, float, int, double>::value() << std::endl; //output: 20 (equal to 8 + 8 + 4) std::cout << pack_size_index<3, double, double, float, int>::value() << std::endl; This gets the job done, but this uses runtime comparison and the resulting executable increases in size rapidly whenever this is used. What's a less expensive way of doing this?

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  • Many users, many cpus, no delays. Good for cloud?

    - by Eric
    I wish to set up a CPU-intensive time-important query service for users on the internet. A usage scenario is described below. Is cloud computing the right way to go for such an implementation? If so, what cloud vendor(s) cater to this type of application? I ask specifically, in terms of: 1) pricing 2) latency resulting from: - slow CPUs, instance creations, JIT compiles, etc.. - internal management and communication of processes inside the cloud (e.g. a queuing process and a calculation process) - communication between cloud and end user 3) ease of deployment A usage scenario I am expecting is: - A typical user sends a query (XML of size around 1K) once every 30 seconds on average. - Each query requires a numerical computation of average time 0.2 sec and max time 1 sec on a 1 GHz Pentium. The computation requires no data other than the query itself and is performed by the same piece of code each time. - The delay a user experiences between sending a query and receiving a response should be on average no more than 2 seconds and in general no more than 5 seconds. - A background save to a DB of the response should occur (not time critical) - There can be up to 30000 simultaneous users - i.e., on average 1000 queries a second, each requiring an average 0.2 sec calculation, so that would necessitate around 200 CPUs. Currently I'm look at GAE Java (for quicker deployment and less IT hassle) and EC2 (Speed and price optimization) as options. Where can I learn more about the right way to set ups such a system? past threads, different blogs, books, etc.. BTW, if my terminology is wrong or confusing, please let me know. I'd greatly appreciate any help.

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  • Interview Q: sorting an almost sorted array (elements misplaced by no more than k)

    - by polygenelubricants
    I was asked this interview question recently: You're given an array that is almost sorted, in that each of the N elements may be misplaced by no more than k positions from the correct sorted order. Find a space-and-time efficient algorithm to sort the array. I have an O(N log k) solution as follows. Let's denote arr[0..n) to mean the elements of the array from index 0 (inclusive) to N (exclusive). Sort arr[0..2k) Now we know that arr[0..k) are in their final sorted positions... ...but arr[k..2k) may still be misplaced by k! Sort arr[k..3k) Now we know that arr[k..2k) are in their final sorted positions... ...but arr[2k..3k) may still be misplaced by k Sort arr[2k..4k) .... Until you sort arr[ik..N), then you're done! This final step may be cheaper than the other steps when you have less than 2k elements left In each step, you sort at most 2k elements in O(k log k), putting at least k elements in their final sorted positions at the end of each step. There are O(N/k) steps, so the overall complexity is O(N log k). My questions are: Is O(N log k) optimal? Can this be improved upon? Can you do this without (partially) re-sorting the same elements?

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  • strtotime not working with TIME?

    - by Prashant
    My mysql column has this datetime value, 2011-04-11 11:00:00 when I am applying strtotime then its returning date less than today,whereas it should be greater than today. also when I am trying this strtotime(date('d/m/Y h:i A')); code, its returning wrong values. Is there any problem with giving TIME in strtotime? Basically I want to do, is to compare my mysql column date with today's date, if its in future then show "Upcoming" else show nothing? Please help and advise, what should I do? Edited code $_startdatetime = $rs['startdatetime']; $_isUpcoming = false; if(!empty($_startdatetime)){ $TEMP_strtime = strtotime($_startdatetime); $TEMP_strtime_today = strtotime(date('d/m/Y h:i A')); if($TEMP_strtime_today < $TEMP_strtime){ $_isUpcoming = true; $_startdatetime = date('l, d F, Y h:i A' ,$TEMP_strtime); } } And the value in $rs['startdatetime'] is 2011-04-11 11:00:00. And with this value I am getting following output. $TEMP_strtime - 1302519600 $TEMP_strtime_today - 1314908160 $_startdatetime - 2011-04-11 11:00:00 $_startdatetime its value is not formatted as the upcoming condition is false, so returning as is mysql value.

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  • Modeling Buyers & Sellers in a Rails Ecommerce App

    - by MikeH
    I'm building a Rails app that has Etsy.com style functionality. In other words, it's like a mall. There are many buyers and many sellers. I'm torn about how to model the sellers. Key facts: There won't be many sellers. Perhaps less than 20 sellers in total. There will be many buyers. Hopefully many thousands :) I already have a standard user model in place with account creation and roles. I've created a 'role' of 'seller', which the admin will manually apply to the proper users. Since we'll have very few sellers, this is not an issue. I'm considering two approaches: (1) Create a 'store' model, which will contain all the relevant store information. Products would :belong_to :store, rather than belonging to the seller. The relationship between the user and store models would be: user :has_one store. My main problem with this is that I've always found has_one associations to be a little funky, and I usually try to avoid them. The app is fairly complex, and I'm worried about running into a cascade of problems connected to the has_one association as I get further along into development. (2) Simply include the relevant 'store' information as part of the user model. But in this case, the store-related db columns would only apply to a very small percentage of users since very few users will also be sellers. I'm not sure if this is a valid concern or not. It's very possible that I'm thinking about this incorrectly. I appreciate any thoughts. Thanks.

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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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  • Need help debugging a huge chunk of JSON data...

    - by meder
    I have a huge chunk, so large that I can't manually edit the file and need to read it in and do regex operations to see what's wrong. Basically - my server is PHP 5.1.6 and I can't update it. This features an older json_decode which is less featured than the 5.2/5.3 versions. json_decode returns NULL and json_last_error is being invoked but the function doesn't exist except in PHP 5.3 so I'm manually trying to see what's wrong. $regex = '#[^0-9"$a-zA-Z{:}().]#'; $json = preg_replace( $regex, '', $json ); $tree = json_decode ( $json, true ); var_dump($tree); // NULL A snippet of the JSON.. somewhere in the middle {"109":0,"103":1,"102":59,"101":70,"100":4299,"94":0,"50":51,"46":0,"45":0,"44":0,"43":0,"42":0,"23":0,"22":0,"18":0,"17":1,"16":1,"13":160,"8":4298}},"2":{"d":{"109":0,"103":92,"102":54,"101":53,"100":4301,"94":0,"50":4278,"49":328,"46":1,"45":0,"44":1,"43":0,"42":0,"26":0,"23":0,"22":0,"18":0,"17":1,"16":1,"8":4300},"m":{"94":1,"100":1,"26":1,"50":1,"8":1,"49":1,"18":1,"43":1,"42":1,"109":1},"c":{"\/":{"d":{"109":0,"100":4301,"94":0,"50":4278,"49":328,"43":0,"42":0,"26":0,"18":0,"8":4300}},"G":{"d":{"109":1,"100":4303,"94":1,"68":17,"50":64,"49":53,"43":1,"42":1,"34":0,"18":1,"13":2216,"11":0,"8":4302}}}},"3": The }}}} is suspicious but this probably just closes 4 nested object literals. Would appreciate any insight.

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