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  • Data Structure for a particular problem??

    - by AGeek
    Hi, Which data structure can perform insertion, deletion and searching operation in O(1) time in the worst case. We may assume the set of elements are integers drawn from a finite set 1,2,...,n, and initialization can take O(n) time. I can only think of implementing a hash table. Implementing it with Trees will not give O(1) time complexity for any of the operation. Or is it possible?? Kindly share your views on this, or any other data structure apart from these.. Thanks..

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  • c# multi threaded file processing

    - by user177883
    There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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  • resizing arrays when close to memory capacity

    - by user548928
    So I am implementing my own hashtable in java, since the built in hashtable has ridiculous memory overhead per entry. I'm making an open-addressed table with a variant of quadratic hashing, which is backed internally by two arrays, one for keys and one for values. I don't have the ability to resize though. The obvious way to do it is to create larger arrays and then hash all of the (key, value) pairs into the new arrays from the old ones. This falls apart though when my old arrays take up over 50% of my current memory, since I can't fit both the old and new arrays in memory at the same time. Is there any way to resize my hashtable in this situation Edit: the info I got for current hashtable memory overheads is from here How much memory does a Hashtable use? Also, for my current application, my values are ints, so rather than store references to Integers, I have an array of ints as my values.

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  • pipelined function

    - by user289429
    Can someone provide an example of how to use parallel table function in oracle pl/sql. We need to run massive queries for 15 years and combine the result. SELECT * FROM Table(TableFunction(cursor(SELECT * FROM year_table))) ...is what we want effectively. The innermost select will give all the years, and the table function will take each year and run massive query and returns a collection. The problem we have is that all years are being fed to one table function itself, we would rather prefer the table function being called in parallel for each of the year. We tried all sort of partitioning by hash and range and it didn't help. Also, can we drop the keyword PIPELINED from the function declaration? because we are not performing any transformation and just need the aggregate of the resultset.

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  • how to sort JTable by providing column index externally.

    - by user345940
    I would like to implement sorting on JTable by providing column index externally in program. Here is my sample code in which i have initialize JTable, Add one Column and 30 rows to JTable. After rows has been added i am sorting JTable by providing column index 0 but i could not get sorted data. how can i get my first column in sorted order? what's wrong with my code. **Why sortCTableonColumnIndex() method could not sort data for specify column index? ` public class Test { private JTable oCTable; private DefaultTableModel oDefaultTableModel; private JScrollPane oPane; private JTableHeader oTableHeader; private TableRowSorter sorter; public void adddata() { for (int i = 0; i < 30; i++) { Object[] row = new Object[1]; String sValueA = "A"; String sValueB = "A"; row[0] = ""; if (i % 2 == 0) { if (i < 15) { sValueA = sValueA + sValueA; row[1] = sValueA; } else { if (i == 16) { sValueB = "D"; row[1] = sValueA; } else { sValueB = sValueB + sValueB; row[1] = sValueA; } } } else { if (i < 15) { sValueB = sValueB + sValueB; row[1] = sValueB; } else { if (i == 17) { sValueB = "C"; row[1] = sValueB; } else { sValueB = sValueB + sValueB; row[1] = sValueB; } } } } } public void createTable() { oCTable = new JTable(); oDefaultTableModel = new DefaultTableModel(); oCTable.setModel(oDefaultTableModel); oTableHeader = oCTable.getTableHeader(); oCTable.setAutoResizeMode(oCTable.AUTO_RESIZE_OFF); oCTable.setFillsViewportHeight(true); JTable oTable = new LineNumberTable(oCTable); oPane = new JScrollPane(oCTable); oPane.setRowHeaderView(oTable); JPanel oJPanel = new JPanel(); oJPanel.setLayout(new BorderLayout()); oJPanel.add(oPane, BorderLayout.CENTER); JDialog oDialog = new JDialog(); oDialog.add(oJPanel); oDialog.setPreferredSize(new Dimension(500, 300)); oDialog.pack(); oDialog.setVisible(true); } public void insert() { oDefaultTableModel.addColumn("Name"); int iColumnPlace = ((DefaultTableModel) oCTable.getModel()).findColumn("Name"); CellRendererForRowHeader oCellRendererForRowHeader = new CellRendererForRowHeader(); TableColumn Column = oCTable.getColumn(oTableHeader.getColumnModel().getColumn(iColumnPlace).getHeaderValue()); Column.setPreferredWidth(300); Column.setMaxWidth(300); Column.setMinWidth(250); Column.setCellRenderer(oCellRendererForRowHeader); for (int i = 0; i < 30; i++) { Object[] row = new Object[1]; String sValueA = "A"; if (i % 2 == 0) { if (i < 15) { sValueA = sValueA + "a"; oDefaultTableModel.insertRow(oCTable.getRowCount(), new Object[]{""}); oDefaultTableModel.setValueAt(sValueA, i, 0); } else { if (i == 16) { sValueA = sValueA + "b"; oDefaultTableModel.insertRow(oCTable.getRowCount(), new Object[]{""}); oDefaultTableModel.setValueAt(sValueA, i, 0); } else { sValueA = sValueA + "c"; oDefaultTableModel.insertRow(oCTable.getRowCount(), new Object[]{""}); oDefaultTableModel.setValueAt(sValueA, i, 0); } } } else { if (i < 15) { sValueA = sValueA + "d"; oDefaultTableModel.insertRow(oCTable.getRowCount(), new Object[]{""}); oDefaultTableModel.setValueAt(sValueA, i, 0); } else { if (i == 17) { sValueA = sValueA + "e"; oDefaultTableModel.insertRow(oCTable.getRowCount(), new Object[]{""}); oDefaultTableModel.setValueAt(sValueA, i, 0); } else { sValueA = sValueA + "f"; oDefaultTableModel.insertRow(oCTable.getRowCount(), new Object[]{""}); oDefaultTableModel.setValueAt(sValueA, i, 0); } } } } } public void showTable() { createTable(); insert(); sortCTableonColumnIndex(0, true); } public void sortCTableonColumnIndex(int iColumnIndex, boolean bIsAsc) { sorter = new TableRowSorter(oDefaultTableModel); List<RowSorter.SortKey> sortKeys = new ArrayList<RowSorter.SortKey>(); if (bIsAsc) { sortKeys.add(new RowSorter.SortKey(iColumnIndex, SortOrder.ASCENDING)); } else { sortKeys.add(new RowSorter.SortKey(iColumnIndex, SortOrder.DESCENDING)); } sorter.setSortKeys(sortKeys); oDefaultTableModel.fireTableStructureChanged(); oCTable.updateUI(); } public static void main(String[] argu) { Test oTest = new Test(); oTest.showTable(); } class CellRendererForRowHeader extends DefaultTableCellRenderer { public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) { JLabel label = null; try { label = (JLabel) super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column); if (column == 0) { label.setBackground(new JLabel().getBackground()); label.setForeground(Color.BLACK); } } catch (RuntimeException ex) { } return label; } } class LineNumberTable extends JTable { private JTable mainTable; public LineNumberTable(JTable table) { super(); mainTable = table; setAutoCreateColumnsFromModel(false); setModel(mainTable.getModel()); setAutoscrolls(false); addColumn(new TableColumn()); getColumnModel().getColumn(0).setCellRenderer(mainTable.getTableHeader().getDefaultRenderer()); getColumnModel().getColumn(0).setPreferredWidth(40); setPreferredScrollableViewportSize(getPreferredSize()); } @Override public boolean isCellEditable(int row, int column) { return false; } @Override public Object getValueAt(int row, int column) { return Integer.valueOf(row + 1); } @Override public int getRowHeight(int row) { return mainTable.getRowHeight(); } } } `

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  • Does to_json require parameters? what about within rails?

    - by Harry Wood
    Does to_json require parameters? what about within rails? I started getting the error "wrong number of arguments (0 for 1)" when doing myhash.to_json Unfortunately I'm not sure when this error started happening, but I guess it relates to some versions of either rails or the json gem. I suppose my code (in a rails controller) is using the ActiveSupport::JSON version of to_json, rather than the to_josn method supported by the json gem. ActiveSupport::JSON vs JSON In environment.rb I have RAILS_GEM_VERSION = '2.3.2' and also config.gem "json", :version=> '1.1.7' It's just a simple hash structure containing primitives which I want to convert in my controller, and it was working, but now I can't seem to run to_json without passing parameters.

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  • which virtualization technology is right for me?

    - by Chris
    I need a little help with this getting this sorted out. I want to setup a linux virtual server that I can use to run both sever and desktop systems. I want a linux system that is minimalist in nature as all the main os will be doing is acting as a hypervisor. The system I'm trying to setup will be running a file server, windows 7, ubuntu 10.04, windows xp and a firewall/gateway security system. All the client OS'es accessing and storing files on the file server. Also all network traffic will be routed through the gateway guest os. The file sever will need direct disk access while the other guests can run one disk images. All of this will be running on the same computer so I wont be romoting in to access the guests OS'es. Also if possible I would like to be able to use my triple head setup in the guest OS'es. I've looked at Xen, kvm and virtualbox but I don't know which is the best for me. I'm really debating between kvm and virtual box as kvm seem to support direct hardware access.

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  • Why use hashing to create pathnames for large collections of files?

    - by Stephen
    Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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  • Best solution for language documentation.

    - by Simone Margaritelli
    I'm developing a new object oriented scripting language and the project itself is quite ready for audience now, so i'm starting to think about a serious (not as "drafty" as it is right now) way of document its grammar, functions from standard library and standard library classes. I've looked a bit around and almost every language hash its own web application for the documentation, Python uses Sphinx for instance. Which is the best PHP (don't have the time/will to install mod_who_knows_what on my server) application to accomplish this? I've used mediawiki a bit but i found its tag system a little bit hard to use in this context. Thanks for your answers.

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  • does a switch idiom make sense in this case?

    - by the ungoverned
    I'm writing a parser/handler for a network protocol; the protocol is predefined and I am writing an adapter, in python. In the process of decoding the incoming messages, I've been considering using the idiom I've seen suggested elsewhere for "switch" in python: use a hash table whose keys are the field you want to match on (a string in this case) and whose values are callable expressions: self.switchTab = { 'N': self.handleN, 'M': self.handleM, ... } Where self.handleN, etc., are methods on the current class. The actual switch looks like this: self.switchTab[selector]() According to some profiling I've done with cProfile (and Python 2.5.2) this is actually a little bit faster than a chain of if..elif... statements. My question is, do folks think this is a reasonable choice? I can't imagine that re-framing this in terms of objects and polymorphism would be as fast, and I think the code looks reasonably clear to a reader.

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  • Killing the mysqld process

    - by Josh K
    I have a table with ~800k rows. I ran an update users set hash = SHA1(CONCAT({about eight fields})) where 1; Now I have a hung Sequel Pro process and I'm not sure about the mysqld process. This is two questions: What harm can possibly come from killing these programs? I'm working on a separate database, so no damage should come to other databases on the system, right? Assume you had to update a table like this. What would be a quicker / more reliable method of updating without writing a separate script. I just checked with phpMyAdmin and it appears as though the query is complete. I still have Sequel Pro using 100% of both my cores though...

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  • How does Hibernate detect dirty state of an entity object?

    - by ???'Lenik
    Is it using some kind of byte codes modification to the original classes? Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version? I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem. If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough. So, the questions are: How does Hibernate know if a property of an object is changed? Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references? And, also, Would hashCode()/equals() with only the id field be enough?

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  • Whats the best data-structure for storing 2-tuple (a, b) which support adding, deleting tuples and c

    - by bhups
    Hi So here is my problem. I want to store 2-tuple (key, val) and want to perform following operations: - keys are strings and values are Integers - multiple keys can have same value - adding new tuples - updating any key with new value (any new value or updated value is greater than the previous one, like timestamps) - fetching all the keys with values less than or greater than given value - deleting tuples. Hash seems to be the obvious choice for updating the key's value but then lookups via values will be going to take longer (O(n)). The other option is balanced binary search tree with key and value switched. So now lookups via values will be fast (O(lg(n))) but updating a key will take (O(n)). So is there any data-structure which can be used to address these issues? Thanks.

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  • How does this Perl grep work to determine the union of several hashes?

    - by titaniumdecoy
    I don't understand the last line of this function from Programming Perl 3e. Here's how you might write a function that does a kind of set intersection by returning a list of keys occurring in all the hashes passed to it: @common = inter( \%foo, \%bar, \%joe ); sub inter { my %seen; for my $href (@_) { while (my $k = each %$href) { $seen{$k}++; } } return grep { $seen{$_} == @_ } keys %seen; } I understand that %seen is a hash which maps each key to the number of times it was encountered in any of the hashes provided to the function.

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  • How can i pass Twig sub parameter?

    - by aliocee
    hi, Help i cant pass my hash key to twig subroutine. here: foreach my $word (sort { $keywords{$a} <=> $keywords{$b} } keys (%keywords)) { my $t = XML::Twig->new( twig_roots => { 'Id' => \&insert($keywords{$word}) } ); $t->parse($docsums); sub insert { my($t, $id, $k)= @_; my $p = $id->text; my $query = "insert into pres (id, wid, p) values(DEFAULT, '$k', '$p')"; my $sql = $connect->prepare($query); $sql->execute( ); } } Thanks.

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  • What's the best way to match a query to a set of keywords?

    - by Ryan Detzel
    Pretty much what you would assume Google does. Advertisers come in and big on keywords, lets say "ipod", "ipod nano", "ipod 60GB", "used ipod", etc. Then we have a query, "I want to buy an ipod nano" or "best place to buy used ipods" what kind of algorithms and systems are used to match those queries to the keyword set. I would imagine that some of those keyword sets are huge, 100k keywords made up of one or more actual words. on top of that queries can be 1-n words as well. Any thoughts, links to wikipedia I can start reading? From what I know already I would use some stemmed hash in disk(CDB?) and a bloom filter to check to see if I should even go to disk.

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  • PHP code cannot see query string param on return in Facebook oAuth flow

    - by TMC
    I am doing some integration with Facebook Open Graph using their oAuth flow and having issues with parsing query string parameters they return. On my callback URL, they pass back an "access_token" parameter with a hash (#). so the callback would be: http://mydomain.com/callback.php#access_token=foobar123 where foobar123 is my access token I'm trying to parse out. However, no matter what I do, my PHP code cannot see if and I've done every debug trick I know (even using phpinfo() to go through everything). The URL is stated only as http://mydomain.com/callback.php. It's as if the rest of the URL isn't really there! This code returns nothing: $token = $_REQUEST['access_token']; Any help would be greatly appreciated... I'm obviously missing something simple.

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  • Pushing Windows Store apps silently

    - by seagull
    As part of a requirement I have been issued, I seek the ability to push apps from the Windows Store (.appx) to remote users. The framework surrounding the data transmission is sorted; What I need to know is if there is a script that can be sent out along with a URI or the package proper to facilitate installation on the user-side of the Windows Store app. I am well aware that numerous guides exist from Microsoft on pushing out Line-of-Business (LOB) (AKA Enterprise) applications -- that is, apps that have been developed in-house and are not for the consumption of the Windows store. This is inappropriate for my requirement, however; the customer wants their clients to receive apps that appear currently on the Windows Store, and for them to be installed in a silent manner. I've seen this guide; http://blogs.technet.com/b/keithmayer/archive/2013/02/25/step-by-step-deploying-windows-8-apps-with-system-center-2012-service-pack-1.aspx, which details doing exactly this, but it is only applicable to machines that are administered by a system running Windows Server 2012 R2 with the 'System Center 2012' bundle installed. The systems I target are considerably more decentralised than this, making this guide inappropriate. I have a hunch that Microsoft have deliberately designed the Windows Store to be this way, but I figured I ought to ask around before I resign myself to the requirement. Much obliged

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  • What's the best way of using a pair (triple, etc) of values as one value in C#?

    - by Yacoder
    That is, I'd like to have a tuple of values. The use case on my mind: Dictionary<Pair<string, int>, object> or Dictionary<Triple<string, int, int>, object> Are there built-in types like Pair or Triple? Or what's the best way of implementing it? Update There are some general-purpose tuples implementations described in the answers, but for tuples used as keys in dictionaries you should additionaly verify correct calculation of the hash code. Some more info on that in another question. Update 2 I guess it is also worth reminding, that when you use some value as a key in dictionary, it should be immutable.

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  • Confusing Perl code

    - by titaniumdecoy
    I don't understand the last line of this function from Programming Perl 3e. Here's how you might write a function that does a kind of set intersection by returning a list of keys occurring in all the hashes passed to it: @common = inter( \%foo, \%bar, \%joe ); sub inter { my %seen; for my $href (@_) { while (my $k = each %$href) { $seen{$k}++; } } return grep { $seen{$_} == @_ } keys %seen; } I understand that %seen is a hash which maps each key to the number of times it was encountered in any of the hashes provided to the function.

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  • Rails application and multilingual content, Model dilemma

    - by dakull
    I'm writing in Rails a website that will be multilingual, for the application translation part i will use the simple I18n gem, for messages and everything related. Yet, all the content must be translated, and we're talking about lots of pages, that will be stored into the database ( like articles, news, etc. ) For now, I'm thinking of two approaches: Lets say i have a Pages table, the content in diff. languages, i will be storing it in a different table called PagesContent that will belong_to Pages and also to a Languages table. The problem here, is that I'll essentially duplicate the no. of tables needed. Pros: flexibility, in the box validation To skip that duplication i can serialize a hash into the content column of Pages, containing the translation. The problem here, is validation, arguably more code to write, and less flexibility when adding a new language. Pros: Less tables. Any other idea ?

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  • ActiveRecord Create (not !) Throwing Exception on Validation

    - by myferalprofessor
    So I'm using ActiveRecord model validations to validate a form in a RESTful application. I have a create action that does: @association = Association.new and the receiving end of the form creates a data hash of attributes from the form parameters to save to the database using: @association = user.associations.create(data) I want to simply render the create action if validation fails. The problem is that the .create (not !) method is throwing an exception in cases where the model validation fails. Example: validates_format_of :url, :with => /(^$)|(^(http|https):\/\/[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(([0-9]{1,5})?\/.*)?$)/ix, :message => "Your url doesn't seem valid." in the model produces: ActiveRecord::RecordInvalid Exception: Validation failed: Url Your url doesn't seem valid. I thought .create! is supposed throw an exception whereas .create is not. Am I missing something here? Ruby 1.8.7 patchlevel 173 & rails 2.3.3

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  • Should I make sure arguments aren't null before using them in a function.

    - by Nathan W
    The title may not really explain what I'm really trying to get at, couldn't really think of a way to describe what I mean. I was wondering if it is good practice to check the arguments that a function accepts for nulls or empty before using them. I have this function which just wraps some hash creation like so. Public Shared Function GenerateHash(ByVal FilePath As IO.FileInfo) As String If (FilePath Is Nothing) Then Throw New ArgumentNullException("FilePath") End If Dim _sha As New Security.Cryptography.MD5CryptoServiceProvider Dim _Hash = Convert.ToBase64String(_sha.ComputeHash(New IO.FileStream(FilePath.FullName, IO.FileMode.Open, IO.FileAccess.Read))) Return _Hash End Function As you can see I just takes a IO.Fileinfo as an argument, at the start of the function I am checking to make sure that it is not nothing. I'm wondering is this good practice or should I just let it get to the actual hasher and then throw the exception because it is null.? Thanks.

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  • how to store passwords in database?

    - by rgksugan
    I use jsp and servlets in my web application. i need to store passwords in the database. I found that hashing will be the best way to do that. I used this code to do it. java.security.MessageDigest d = null; d = java.security.MessageDigest.getInstance("SHA-1"); d.reset(); d.update(pass.getBytes("UTF-8")); byte b[] = d.digest(); String tmp = (new BASE64Encoder()).encode(b); When i tried to print the value of tmp, i get some other value.i guess its the hash value of the password. But when i persist this data to the database the original password gets saved there other than the value in tmp.. What is the problem???

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  • What is the best way to implement this composite GetHashCode()

    - by Frank Krueger
    I have a simple class: public class TileName { int Zoom, X, Y; public override bool Equals (object obj) { var o = obj as TileName; return (o != null) && (o.Zoom == Zoom) && (o.X == X) && (o.Y == Y); } public override int GetHashCode () { return (Zoom + X + Y).GetHashCode(); } } I was curious if I would get a better distribution of hash codes if I instead did something like: public override int GetHashCode () { return Zoom.GetHashCode() + X.GetHashCode() + Y.GetHashCode(); } This class is going to be used as a Dictionary key, so I do want to make sure there is a decent distribution.

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