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  • Setting up a server that routes local traffic through vpn, while still being able to access internet directly

    - by Kazuo
    The goal is to setup a local server that routes local traffic through an uncontrolled remote vpn service while still being able to access the internet directly (not tunneled via vpn) and provide services through that direct connection. It is supposed to look like this: http://i.stack.imgur.com/74dGC.png Note: There is another router with modem between the local server and the internet. What is the easiest (best?) way to get this network setup working? I'm planning to setup the connection between the local router and the local server with simple ip forwarding. The problem now is that all the server's traffic is routed through the vpn tunnel as soon as I connect the server's openvpn client to the remote service so there is no direct internet connection available. My first idea was to setup a virtual machine (lxc container or something) and run the vpn client and local networking stuff in the vm. So that the vm receives all the incoming traffic from the local router and tunnels it through the vpn. This, as far as I understand, should not affect the physical server's network connection and should allow it to provide services to the internet. Before I start trying to set this up (I don't have much experience in networking), is there any easier or better way to do this? I would be thankful for every suggestion. Edit: Let's say the interface connected to the internet is eth0 and the interface connected to the local router is eth1. Another idea would be to create a virtual interface eth0:0 and specifiy it as openvpn's local endpoint and then force any traffic coming from eth1 through eth0:0. I'm not sure how I would force the traffic through eth0:0, though (possibly by adding routes).

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  • Mac OS X: Applications not responding

    - by Robot55
    This happens to me several times a day. I'll quit an app, the window will close, but the app won't finish shutting down. It stays open in the dock, and right clicking and force quit show not responding. Force quit won't work. I can't shut the app down. Starting any other app when this happens causes that app to behave in exactly the same way: the icon opens in the dock, but the app is non-responsive and can't be forced to quit. Can't access terminal when this happens, because it locks up just like all the apps. While I haven't tried to open every app, I think any app I try to open when this is happening will lock up. If I relaunch Finder, it too locks up and then the only thing left is to hold down the power button for a hard reboot. Any app that is running while this is happening will continue to run normally unless I try to shut it down. Repairing disk permissions has no effect. I also did a time machine and a full restore on a brand new MbP - and sure enough, after restore, the new MbP suffers form the same problem. Creating a new user has no effect. Any thoughts? Please help MacBook Pro 15" AG 2.53ghz i5 cpu 8gb RAM 500gb HD (over 200gb free)

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  • [GEEK SCHOOL] Network Security 1: Securing User Accounts and Passwords in Windows

    - by Matt Klein
    This How-To Geek School class is intended for people who want to learn more about security when using Windows operating systems. You will learn many principles that will help you have a more secure computing experience and will get the chance to use all the important security tools and features that are bundled with Windows. Obviously, we will share everything you need to know about using them effectively. In this first lesson, we will talk about password security; the different ways of logging into Windows and how secure they are. In the proceeding lesson, we will explain where Windows stores all the user names and passwords you enter while working in this operating systems, how safe they are, and how to manage this data. Moving on in the series, we will talk about User Account Control, its role in improving the security of your system, and how to use Windows Defender in order to protect your system from malware. Then, we will talk about the Windows Firewall, how to use it in order to manage the apps that get access to the network and the Internet, and how to create your own filtering rules. After that, we will discuss the SmartScreen Filter – a security feature that gets more and more attention from Microsoft and is now widely used in its Windows 8.x operating systems. Moving on, we will discuss ways to keep your software and apps up-to-date, why this is important and which tools you can use to automate this process as much as possible. Last but not least, we will discuss the Action Center and its role in keeping you informed about what’s going on with your system and share several tips and tricks about how to stay safe when using your computer and the Internet. Let’s get started by discussing everyone’s favorite subject: passwords. The Types of Passwords Found in Windows In Windows 7, you have only local user accounts, which may or may not have a password. For example, you can easily set a blank password for any user account, even if that one is an administrator. The only exception to this rule are business networks where domain policies force all user accounts to use a non-blank password. In Windows 8.x, you have both local accounts and Microsoft accounts. If you would like to learn more about them, don’t hesitate to read the lesson on User Accounts, Groups, Permissions & Their Role in Sharing, in our Windows Networking series. Microsoft accounts are obliged to use a non-blank password due to the fact that a Microsoft account gives you access to Microsoft services. Using a blank password would mean exposing yourself to lots of problems. Local accounts in Windows 8.1 however, can use a blank password. On top of traditional passwords, any user account can create and use a 4-digit PIN or a picture password. These concepts were introduced by Microsoft to speed up the sign in process for the Windows 8.x operating system. However, they do not replace the use of a traditional password and can be used only in conjunction with a traditional user account password. Another type of password that you encounter in Windows operating systems is the Homegroup password. In a typical home network, users can use the Homegroup to easily share resources. A Homegroup can be joined by a Windows device only by using the Homegroup password. If you would like to learn more about the Homegroup and how to use it for network sharing, don’t hesitate to read our Windows Networking series. What to Keep in Mind When Creating Passwords, PINs and Picture Passwords When creating passwords, a PIN, or a picture password for your user account, we would like you keep in mind the following recommendations: Do not use blank passwords, even on the desktop computers in your home. You never know who may gain unwanted access to them. Also, malware can run more easily as administrator because you do not have a password. Trading your security for convenience when logging in is never a good idea. When creating a password, make it at least eight characters long. Make sure that it includes a random mix of upper and lowercase letters, numbers, and symbols. Ideally, it should not be related in any way to your name, username, or company name. Make sure that your passwords do not include complete words from any dictionary. Dictionaries are the first thing crackers use to hack passwords. Do not use the same password for more than one account. All of your passwords should be unique and you should use a system like LastPass, KeePass, Roboform or something similar to keep track of them. When creating a PIN use four different digits to make things slightly harder to crack. When creating a picture password, pick a photo that has at least 10 “points of interests”. Points of interests are areas that serve as a landmark for your gestures. Use a random mixture of gesture types and sequence and make sure that you do not repeat the same gesture twice. Be aware that smudges on the screen could potentially reveal your gestures to others. The Security of Your Password vs. the PIN and the Picture Password Any kind of password can be cracked with enough effort and the appropriate tools. There is no such thing as a completely secure password. However, passwords created using only a few security principles are much harder to crack than others. If you respect the recommendations shared in the previous section of this lesson, you will end up having reasonably secure passwords. Out of all the log in methods in Windows 8.x, the PIN is the easiest to brute force because PINs are restricted to four digits and there are only 10,000 possible unique combinations available. The picture password is more secure than the PIN because it provides many more opportunities for creating unique combinations of gestures. Microsoft have compared the two login options from a security perspective in this post: Signing in with a picture password. In order to discourage brute force attacks against picture passwords and PINs, Windows defaults to your traditional text password after five failed attempts. The PIN and the picture password function only as alternative login methods to Windows 8.x. Therefore, if someone cracks them, he or she doesn’t have access to your user account password. However, that person can use all the apps installed on your Windows 8.x device, access your files, data, and so on. How to Create a PIN in Windows 8.x If you log in to a Windows 8.x device with a user account that has a non-blank password, then you can create a 4-digit PIN for it, to use it as a complementary login method. In order to create one, you need to go to “PC Settings”. If you don’t know how, then press Windows + C on your keyboard or flick from the right edge of the screen, on a touch-enabled device, then press “Settings”. The Settings charm is now open. Click or tap the link that says “Change PC settings”, on the bottom of the charm. In PC settings, go to Accounts and then to “Sign-in options”. Here you will find all the necessary options for changing your existing password, creating a PIN, or a picture password. To create a PIN, press the “Add” button in the PIN section. The “Create a PIN” wizard is started and you are asked to enter the password of your user account. Type it and press “OK”. Now you are asked to enter a 4-digit pin in the “Enter PIN” and “Confirm PIN” fields. The PIN has been created and you can now use it to log in to Windows. How to Create a Picture Password in Windows 8.x If you log in to a Windows 8.x device with a user account that has a non-blank password, then you can also create a picture password and use it as a complementary login method. In order to create one, you need to go to “PC settings”. In PC Settings, go to Accounts and then to “Sign-in options”. Here you will find all the necessary options for changing your existing password, creating a PIN, or a picture password. To create a picture password, press the “Add” button in the “Picture password” section. The “Create a picture password” wizard is started and you are asked to enter the password of your user account. You are shown a guide on how the picture password works. Take a few seconds to watch it and learn the gestures that can be used for your picture password. You will learn that you can create a combination of circles, straight lines, and taps. When ready, press “Choose picture”. Browse your Windows 8.x device and select the picture you want to use for your password and press “Open”. Now you can drag the picture to position it the way you want. When you like how the picture is positioned, press “Use this picture” on the left. If you are not happy with the picture, press “Choose new picture” and select a new one, as shown during the previous step. After you have confirmed that you want to use this picture, you are asked to set up your gestures for the picture password. Draw three gestures on the picture, any combination you wish. Please remember that you can use only three gestures: circles, straight lines, and taps. Once you have drawn those three gestures, you are asked to confirm. Draw the same gestures one more time. If everything goes well, you are informed that you have created your picture password and that you can use it the next time you sign in to Windows. If you don’t confirm the gestures correctly, you will be asked to try again, until you draw the same gestures twice. To close the picture password wizard, press “Finish”. Where Does Windows Store Your Passwords? Are They Safe? All the passwords that you enter in Windows and save for future use are stored in the Credential Manager. This tool is a vault with the usernames and passwords that you use to log on to your computer, to other computers on the network, to apps from the Windows Store, or to websites using Internet Explorer. By storing these credentials, Windows can automatically log you the next time you access the same app, network share, or website. Everything that is stored in the Credential Manager is encrypted for your protection.

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  • Download Angry Birds For Windows 7 & Windows XP

    - by Gopinath
    The famous Angry Birds game from Rovio is now available for your personal computers. You can download the game from Intel’s App Store for windows. It costs $5 and supported on Windows 7 and Windows XP computers. Here is a video of Angry Birds running on Windows 7 Laptop. The survival of the Angry Birds is at stake. Dish out revenge on the green pigs who stole the Birds’ eggs. Use the unique destructive powers of the Angry Birds to lay waste to the pigs’ fortifications. Angry Birds features hours and hours of challenging physics-based demolition gameplay, with lots of replay value. Each level requires a mixture of logic, skill, and brute force to crush the enemy. Download Angry Birds For PCs From Intel AppUp This article titled,Download Angry Birds For Windows 7 & Windows XP, was originally published at Tech Dreams. Grab our rss feed or fan us on Facebook to get updates from us.

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  • Raleigh theme on LightDM, Ubuntu desktop, Nautilus window, menus & menu-bars

    - by Tassos Seligkas
    After performing an upgrade from Natty to Oneiric, I had a problem similar to the one reported in here at every system boot: Desktop forgets theme? Everything, from the LigthDM greeter to the ubuntu desktop used the ugly raleigh theme, apart from firefox, thunderbird few other applications after logging in. Unfortunately none of the solutions suggested in the topic above worked for me. The only way I could get acceptable appearance would be to switch to gnome at login and using the Adwaita theme. The lightdm greeter still uses the raleigh theme though. Unfortunately, I tried some "brute-force" methods by reinstalling (sudo apt-get install --reinstall) ubuntu-desktop, unity, unity-common, unity-greeter, gnome-session, gtk2-engines. I also tried moving .config, .gconf, .gconfd, .gnome, .gnome2 to a backup dir to reset account desktop preferences. None of the above solved the issue. On the contrary, logging-in to Ubuntu setup does not show unity and window decorations anymore. My fallback remains the Gnome logon and the Adwaita theme. This is my workstation machine I am hosting Ubuntu on, so, though possible, it is time consuming to perform a backup and format-reinstall ubuntu 11.10. Could you please let me know if I can get an alternative way of repairing my ubuntu desktop? (I believe it all started when, during the 11.04-to-11.10 upgrade, the installation of downloaded packages for oneiric broke when nautilus-dropbox failed to access the dropbox servers - I am behind a proxy but with proper proxy settings had no problems using apt-get & synaptic. However I removed dropbox and resumed partial installation on second boot.)

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  • What is the most time-effective way to monitor & manage threats from bots and/or humans?

    - by CheeseConQueso
    I'm usually overwhelmed by the amount of tools that hosting companies provide to track & quantify traffic data and statistics. I'm equally overwhelmed by the countless flavors of malicious 'attacks' that target any and every web site known to man. The security methods used to protect both the back and front end of a website are documented well and are straight-forward in terms of ease of implementation and application, but the army of autonomous bots knows no boundaries and will always find a niche of a website to infest. So what can be done to handle the inevitable swarm of bots that pound your domain with brute force? Whenever I look at error logs for my domains, there are always thousands of entries that look like bots trying to sneak sql code into the database by tricking the variables in the url into giving them schema information or private data within the database. My barbaric and time-consuming plan of defense is just to monitor visitor statistics for those obvious patterns of abuse and either ban the ips or range of ips accordingly. Aside from that, I don't know much else I could do to prevent all of the ping pong going on all day. Are there any good tools that automatically monitor this background activity (specifically activity that throws errors on the web & db server) and proactively deal with these source(s) of mayhem?

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  • Collision detection on a 2D hexagonal grid

    - by SundayMonday
    I'm making a casual grid-based 2D iPhone game using Cocos2D. The grid is a "staggered" hex-like grid consisting of uniformly sized and spaced discs. It looks something like this. I've stored the grid in a 2D array. Also I have a concept of "surrounding" grid cells. Namely the six grid cells surrounding a particular cell (except those on the boundries which can have less than six). Anyways I'm testing some collision detection and it's not working out as well as I had planned. Here's how I currently do collision detection for a moving disc that's approaching the stationary group of discs: Calculate ij-coordinates of grid cell closest to moving cell using moving cell's xy-position Get list of surrounding grid cells using ij-coordinates Examine the surrounding cells. If they're all empty then no collision If we have some non-empty surrounding cells then compare the distance between the disc centers to some minimum distance required for a collision If there's a collision then place the moving disc in grid cell ij So this works but not too well. I've considered a potentially simpler brute force approach where I just compare the moving disc to all stationary discs at each step of the game loop. This is probably feasible in terms of performance since the stationary disc count is 300 max. If not then some space-partitioning data structure could be used however that feels too complex. What are some common approaches and best practices to collision detection in a game like this?

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  • Is SHA-1 secure for password storage?

    - by Tgr
    Some people throw around remarks like "SHA-1 is broken" a lot, so I'm trying to understand what exactly that means. Let's assume I have a database of SHA-1 password hashes, and an attacker whith a state of the art SHA-1 breaking algorithm and a botnet with 100,000 machines gets access to it. (Having control over 100k home computers would mean they can do about 10^15 operations per second.) How much time would they need to find out the password of any one user? find out the password of a given user? find out the password of all users? find a way to log in as one of the users? find a way to log in as a specific user? How does that change if the passwords are salted? Does the method of salting (prefix, postfix, both, or something more complicated like xor-ing) matter? Here is my current understanding, after some googling. Please correct in the answers if I misunderstood something. If there is no salt, a rainbow attack will immediately find all passwords (except extremely long ones). If there is a sufficiently long random salt, the most effective way to find out the passwords is a brute force or dictionary attack. Neither collision nor preimage attacks are any help in finding out the actual password, so cryptographic attacks against SHA-1 are no help here. It doesn't even matter much what algorithm is used - one could even use MD5 or MD4 and the passwords would be just as safe (there is a slight difference because computing a SHA-1 hash is slower). To evaluate how safe "just as safe" is, let's assume that a single sha1 run takes 1000 operations and passwords contain uppercase, lowercase and digits (that is, 60 characters). That means the attacker can test 1015*60*60*24 / 1000 ~= 1017 potential password a day. For a brute force attack, that would mean testing all passwords up to 9 characters in 3 hours, up to 10 characters in a week, up to 11 characters in a year. (It takes 60 times as much for every additional character.) A dictionary attack is much, much faster (even an attacker with a single computer could pull it off in hours), but only finds weak passwords. To log in as a user, the attacker does not need to find out the exact password; it is enough to find a string that results in the same hash. This is called a first preimage attack. As far as I could find, there are no preimage attacks against SHA-1. (A bruteforce attack would take 2160 operations, which means our theoretical attacker would need 1030 years to pull it off. Limits of theoretical possibility are around 260 operations, at which the attack would take a few years.) There are preimage attacks against reduced versions of SHA-1 with negligible effect (for the reduced SHA-1 which uses 44 steps instead of 80, attack time is down from 2160 operations to 2157). There are collision attacks against SHA-1 which are well within theoretical possibility (the best I found brings the time down from 280 to 252), but those are useless against password hashes, even without salting. In short, storing passwords with SHA-1 seems perfectly safe. Did I miss something?

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  • SQL Query for Determining SharePoint ACL Sizes

    - by Damon Armstrong
    When a SharePoint Access Control List (ACL) size exceeds more than 64kb for a particular URL, the contents under that URL become unsearchable due to limitations in the SharePoint search engine.  The error most often seen is The Parameter is Incorrect which really helps to pinpoint the problem (its difficult to convey extreme sarcasm here, please note that it is intended).  Exceeding this limit is not unheard of – it can happen when users brute force security into working by continually overriding inherited permissions and assigning user-level access to securable objects. Once you have this issue, determining where you need to focus to fix the problem can be difficult.  Fortunately, there is a query that you can run on a content database that can help identify the issue: SELECT [SiteId],      MIN([ScopeUrl]) AS URL,      SUM(DATALENGTH([Acl]))/1024 as AclSizeKB,      COUNT(*) AS AclEntries FROM [Perms] (NOLOCK) GROUP BY siteid ORDER BY AclSizeKB DESC This query results in a list of ACL sizes and entry counts on a site-by-site basis.  You can also remove grouping to see a more granular breakdown: SELECT [ScopeUrl] AS URL,       SUM(DATALENGTH([Acl]))/1024 as AclSizeKB,      COUNT(*) AS AclEntries FROM [Perms] (NOLOCK) GROUP BY ScopeUrl ORDER BY AclSizeKB DESC

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  • How do you avoid jumping to a solution when under pressure? [closed]

    - by GlenPeterson
    When under a particularly strict programming deadline (like an hour), if I panic at all, my tendency is to jump into coding without a real plan and hope I figure it out as I go along. Given enough time, this can work, but in an interview it's been pretty unsuccessful, if not downright counter-productive. I'm not always comfortable sitting there thinking while the clock ticks away. Is there a checklist or are there techniques to recognize when you understand the problem well enough to start coding? Maybe don't touch the keyboard for the first 5-10 minutes of the problem? At what point do you give up and code a brute-force solution with the hope of reasoning out a better solution later? A related follow-up question might be, "How do you ensure that you are solving the right problem?" Or "When is it most productive to think and design more vs. code some experiments to and figure out the design later?" EDIT: One close vote already, but I'm not sure why. I wrote this in the first person, but I doubt I'm the only programmer to ever choke in an interview. Here is a list of techniques for taking a math test and another for taking an oral exam. Maybe I'm not expressing myself well, but I'm asking if there is a similar list of techniques for handling a programming problem under pressure?

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  • Discovering path through unknown territory

    - by TravisG
    Let's say all the AI knows about it's surroundings is a pixel-map that it has which clearly shows walkable terrain and obstacles. I want the AI to be able to traverse this terrain until it finds an exit point. There are some restrictions: There is always a way to the exit in the entire map that the AI walks around in, but there may be dead ends. The path to the exit is always pretty random, meaning that if you stand at crossroads, nothing indicates which direction would be the right one to go. It doesn't matter if the AI reaches a dead end, but it has to be able walk back out of it to a previously not inspected location and continue its search there. Initially, the AI starts out knowing only the starting area of the whole map. As it walks around, new points will be added to the pixel-map as the AI corresponding to the AIs range of sight (think of it like the AI is clearing the fog of war) The problem is in 2D space. All I have is the pixel map. There are no paths in the pixel map which are "too narrow". The AI fits through everything. It shouldn't be a brute force solution. E.g. it would be possible to simply find a path to each pixel in the pixel map that is yet undiscovered (with A*, for example), which will lead to the AI discovering new pixels. This could be repeated until the end is reached. The path doesn't have to be the shortest path (this is impossible without knowing the entire map beforehand), but when movements within the visible area are calculated, the shortest and from a human standpoint most logical path should be taken (e.g. if you can see a way out of your room into a hallway, you would obviously go there instead of exploring the corner of your current room). What kind of approaches to solve this problem are there?

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  • A new mission statement for my school's algorithms class

    - by Eric Fode
    The teacher at Eastern Washington University that is now teaching the algorithms course is new to eastern and as a result the course has changed drastically mostly in the right direction. That being said I feel that the class could use a more specific, and industry oriented (since that is where most students will go, though suggestions for an academia oriented class are also welcome) direction, having only worked in industry for 2 years I would like the community's (a wider and much more collectively experienced and in the end plausibly more credible) opinion on the quality of this as a statement for the purpose an algorithms class, and if I am completely off target your suggestion for the purpose of a required Jr. level Algorithms class that is standalone (so no other classes focusing specifically on algorithms are required). The statement is as follows: The purpose of the algorithms class is to do three things: Primarily, to teach how to learn, do basic analysis, and implement a given algorithm found outside of the class. Secondly, to teach the student how to model a problem in their mind so that they can find a an existing algorithm or have a direction to start the development of a new algorithm. Third, to overview a variety of algorithms that exist and to deeply understand and analyze one algorithm in each of the basic algorithmic design strategies: Divide and Conquer, Reduce and Conquer, Transform and Conquer, Greedy, Brute Force, Iterative Improvement and Dynamic Programming. The Question in short is: do you agree with this statement of the purpose of an algorithms course, so that it would be useful in the real world, if not what would you suggest?

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  • How to parse JSON data from web more faster [closed]

    - by Kaidul Islam Sazal
    I have json inventory inventory.json on the server like this: [ { "body" : "SUV", "color" : { "ext" : "White diamond pearl", "int" : "Taupe" }, "id" : "276181", "make" : "Acura", "miles" : 35949, "model" : "RDX", "pic" : [ { "full" : "http://images1.dealercp.com/90961/000JNBD/001_0292.jpg" } ], "power" : { "drive" : "Front wheel drive", "eng" : "2.3L DOHC PGM-FI 16-VALVE", "trans" : "Automatic" }, "price" : { "net" : 29488 }, "stock" : "6942", "trim" : "AWD 4dr Tech Pkg SUV", "vin" : "5J8TB2H53BA000334", "year" : 2011 }, { "body" : "Sedan", "color" : { "ext" : "Premium white pearl", "int" : "Taupe" }, "id" : "275622", "make" : "Acura", "miles" : 40923, "model" : "TSX", "pic" : [ { "full" : "http://images1.dealercp.com/90961/000JMC6/001_1765.jpg" } ], "power" : { "drive" : "Front wheel drive", "eng" : "2.4L L4 MPI DOHC 16V", "trans" : "Automatic" }, "price" : { "net" : 22288 }, "stock" : "6945", "trim" : "4dr Sdn I4 Auto Sedan", "vin" : "JH4CU2F66AC011933", "year" : 2010 } ] here are two index, There are almost 5000 index like this. I parsed this json like this: var url = "inventory/inventory.json"; $.getJSON(url, function(data){ $.each(data, function(index, item){ //straight-forward loop if(item.year == 2012) { $('#desc').append(item.make + ' ' + item.model + ' ' + '<br/>' + item.price.net + '<br/>' + item.pic[0].full); } }); }); This is working fine.But the problem is that, this searching and fetching process is little bit slow as there are 5000 indexes already and it's increasing day by day. It seems that, it is a straight-forward loop to parse the data and a normal brute-force method. Now I want to know if there any time efiicient way to parse more faster.Any faster method to parse instead of straight-forward loop ?

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  • How do client-server cooperation based games like Diablo 3 work?

    - by edgar
    Diablo 3 cooperates with Blizzard servers even during single player games. In fact, Blizzard has had problems with the games "melting their servers." I would like to ask: How do the client and the server communicate? What details does the client leave to the server, and vice versa? What details are redundant - both the client and the server know - and how often do they disagree? The previous paragraph contains the important questions, but I have a few more that I must explain my motivation towards. I am interested in the programming of botting. Ethical botting - I don't plan on actually abusing the automation to run 24/7. I just find it to be a great programming challenge to glean information from a game, and then make decisions from that information. I am stuck in the starting gate. The unofficial questions from this post would be: How can I make a bot (language, tools, libraries)? Can I get information through the communication between client and server, rather than the brute force pixel detection easily used in more static games? There probably is a trust issue, and to that all I can say is that I promise not to abuse the answers. But please feel free to answer any of the questions you feel comfortable with. Thank you!

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  • Count function on tree structure (non-binary)

    - by Spevy
    I am implementing a tree Data structure in c# based (largely on Dan Vanderboom's Generic implementation). I am now considering approach on handling a Count property which Dan does not implement. The obvious and easy way would be to use a recursive call which Traverses the tree happily adding up nodes (or iteratively traversing the tree with a Queue and counting nodes if you prefer). It just seems expensive. (I also may want to lazy load some of my nodes down the road). I could maintain a count at the root node. All children would traverse up to and/or hold a reference to the root, and update a internally settable count property on changes. This would push the iteration problem to when ever I want to break off a branch or clear all children below a given node. Generally less expensive, and puts the heavy lifting what I think will be less frequently called functions. Seems a little brute force, and that usually means exception cases I haven't thought of yet, or bugs if you prefer. Does anyone have an example of an implementation which keeps a count for an Unbalanced and/or non-binary tree structure rather than counting on the fly? Don't worry about the lazy load, or language. I am sure I can adjust the example to fit my specific needs. EDIT: I am curious about an example, rather than instructions or discussion. I know this is not technically difficult...

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  • algorithm for Virtual Machine(VM) Consolidation in Cloud

    - by devansh dalal
    PROBLEM: We have N physical machines(PMs) each with ram Ri, cpu Ci and a set of currently scheduled VMs each with ram requirement ri and ci respectively Moving(Migrating) any VM from one PM to other has a cost associated which depends on its ram ri. A PM with no VMs is shut down to save power. Our target is to minimize the weighted sum of (N,migration cost) by migrating some VMs i.e. minimize the number of working PMs as well as not to degrade the service level due to excessive migrations. My Approach: Brute Force approach is choosing the minimum loaded PM and try to fit its VMs to other PMs by First Fit Decreasing algorithm or we can select the victim PMs and target PMs based on their loading level and shut down victims if possible by moving their VMs to targets. I tried this Greedy approach on the Data of Baadal(IIT-D cloud) but It isn't giving promising results. I have also tried to study the Ant colony optimization for dynamic VM consolidating but was unable to understand very much. I used the links. http://dumas.ccsd.cnrs.fr/docs/00/72/52/15/PDF/Esnault.pdf http://hal.archives-ouvertes.fr/docs/00/72/38/56/PDF/RR-8032.pdf Would anyone please explain the solution or suggest any new approach for better performance soon. Thanks in advance.

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  • Name of the Countdown Numbers round problem - and algorithmic solutions?

    - by Dai
    For the non-Brits in the audience, there's a segment of a daytime game-show where contestants have a set of 6 numbers and a randomly generated target number. They have to reach the target number using any (but not necessarily all) of the 6 numbers using only arithmetic operators. All calculations must result in positive integers. An example: Youtube: Countdown - The Most Extraordinary Numbers Game Ever? A detailed description is given on Wikipedia: Countdown (Game Show) For example: The contentant selects 6 numbers - two large (possibilities include 25, 50, 75, 100) and four small (numbers 1 .. 10, each included twice in the pool). The numbers picked are 75, 50, 2, 3, 8, 7 are given with a target number of 812. One attempt is (75 + 50 - 8) * 7 - (3 * 2) = 813 (This scores 7 points for a solution within 5 of the target) An exact answer would be (50 + 8) * 7 * 2 = 812 (This would have scored 10 points exactly matching the target). Obviously this problem has existed before the advent of TV, but the Wikipedia article doesn't give it a name. I've also saw this game at a primary school I attended where the game was called "Crypto" as an inter-class competition - but searching for it now reveals nothing. I took part in it a few times and my dad wrote an Excel spreadsheet that attempted to brute-force the problem, I don't remember how it worked (only that it didn't work, what with Excel's 65535 row limit), but surely there must be an algorithmic solution for the problem. Maybe there's a solution that works the way human cognition does (e.g. in-parallel to find numbers 'close enough', then taking candidates and performing 'smaller' operations).

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  • How to avoid jumping to a solution when under pressure? [closed]

    - by GlenPeterson
    When under a particularly strict programming deadline (like an hour), if I panic at all, my tendency is to jump into coding without a real plan and hope I figure it out as I go along. Given enough time, this can work, but in an interview it's been pretty unsuccessful, if not downright counter-productive. I'm not always comfortable sitting there thinking while the clock ticks away. Is there a checklist or are there techniques to recognize when you understand the problem well enough to start coding? Maybe don't touch the keyboard for the first 5-10 minutes of the problem? At what point do you give up and code a brute-force solution with the hope of reasoning out a better solution later? When is it most productive to think and design more vs. code some experiments to and figure out the design later? Here is a list of techniques for taking a math test and another for taking an oral exam. Is there is a similar list of techniques for handling a programming problem under pressure? ANSWERS: I think this is a valid answer: How To Solve It. I found the link as an answer to Steps to solve or approach towards a solution. There were also some really good tips at Is thinking out loud during an interview really the best strategy?. A great and concise argument for TDD is the first answer to TDD Writing code vs Figuring out the answer to a problem?. My question may be a near-duplicate of that one.

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  • Efficient algorithm for Virtual Machine(VM) Consolidation in Cloud

    - by devansh dalal
    PROBLEM: We have N physical machines(PMs) each with ram Ri, cpu Ci and a set of currently scheduled VMs each with ram requirement ri and ci respectively Moving(Migrating) any VM from one PM to other has a cost associated which depends on its ram ri. A PM with no VMs is shut down to save power. Our target is to minimize the weighted sum of (N,migration cost) by migrating some VMs i.e. minimize the number of working PMs as well as not to degrade the service level due to excessive migrations. My Approach: Brute Force approach is choosing the minimum loaded PM and try to fit its VMs to other PMs by First Fit Decreasing algorithm or we can select the victim PMs and target PMs based on their loading level and shut down victims if possible by moving their VMs to targets. I tried this Greedy approach on the Data of Baadal(IIT-D cloud) but It isn't giving promising results. I have also tried to study the Ant colony optimization for dynamic VM consolidating but was unable to understand very much. I used the links. http://dumas.ccsd.cnrs.fr/docs/00/72/52/15/PDF/Esnault.pdf http://hal.archives-ouvertes.fr/docs/00/72/38/56/PDF/RR-8032.pdf Would anyone please clarify the solution or suggest any new approach/resources for better performance. I am basically searching for the algorithms not the physical optimizations and I also know that many commercial organizations have provided these solution but I just wanted to know more the underlying algorithms. Thanks in advance.

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  • Determining whether two fast moving objects should be submitted for a collision check

    - by dreta
    I have a basic 2D physics engine running. It's pretty much a particle engine, just uses basic shapes like AABBs and circles, so no rotation is possible. I have CCD implemented that can give accurate TOI for two fast moving objects and everything is working smoothly. My issue now is that i can't figure out how to determine whether two fast moving objects should even be checked against each other in the first place. I'm using a quad tree for spacial partitioning and for each fast moving object, i check it against objects in each cell that it passes. This works fine for determining collision with static geometry, but it means that any other fast moving object that could collide with it, but isn't in any of the cells that are checked, is never considered. The only solution to this i can think of is to either have the cells large enough and cross fingers that this is enough, or to implement some sort of a brute force algorithm. Is there a proper way of dealing with this, maybe somebody solved this issue in an efficient manner. Or maybe there's a better way of partitioning space that accounts for this?

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  • Do i need to restore iptable rules everytime on boot?

    - by capdragon
    Every time i reboot i loose the iptables rules that took me sooo long to enter. I know i can save them and restore them on boot but is there anyway to save them forever? Do i really need to restore them on boot every time? Seriously? The problem is I have a HUGE list of IPs in which i use a while loop to load them in. This can take upwards of 10 minutes. This is my home FTP server. It's a small vm with 1gb ram and very little processing power. There are so many IPs because I've pretty much given up on the Asian continent. I don't need them to be hitting up my ftp server everyday with brute force. I also block gov. monitors, trackers and spammers. This is the while loop i use to load in the list. grep INPUT block.list | while read LISTA; do sudo iptables -A $LISTA; done

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  • Has the emerging generation of programmers got the wrong idea about design patterns? [closed]

    - by MattDavey
    Over the years I've noticed a shift in attitude towards design patterns, particularly amongst the emerging generation of developers. There seems to be a notion these days that design patterns are silver bullets that instantly cure any problem, a proliferating idea that advancing as a software engineer simply means learning and applying more and more patterns. When confronted with a problem, developers no longer strive to truly understand the issue and design a solution - instead they simply pick a design pattern which seems to be a close fit, and try to brute-force it. You can see evidence of this by the many, many questions on Stack Overflow that begin with the phrase "what pattern should I use to...". I fall into a slightly more mature category of developers (5-10 years experience) and I have a very different viewpoint on patterns - simply as a communication tool to enhance clarity. I find this perspective of design patterns being lego bricks (collected like pokemon cards) a little disconcerting. Will developers lose this attitude as they gain more experience in software engineering? Or could these notions perhaps steer the direction of our craft in years to come? Did the older generation of developers have any similar concerns about us? (perhaps about OO design or similar...). if so, how did we turn out?

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  • Trying to sort the coefficients of the polynomial (z-a)(z-b)(z-c)...(z-n) into a vector

    - by pajamas
    So I have a factored polynomial of the form (z-a)(z-b)(z-c)...(z-n) for n an even positive integer. Thus the coefficient of z^k for 0 <= k < n will be the sum of all distinct n-k element products taken from the set {a,b,...,n} multiplied by (-1)^k, I hope that makes sense, please ask if you need more clarification. I'm trying to put these coefficients into a row vector with the first column containing the constant coefficient (which would be abc...n) and the last column containing the coefficient for z^n (which would be 1). I imagine there is a way to brute force this with a ton of nested loops, but I'm hoping there is a more efficient way. This is being done in Matlab (which I'm not that familiar with) and I know Matlab has a ton of algorithms and functions, so maybe its got something I can use. Can anyone think of a way to do this? Example: (z-1)(z-2)(z-3) = z^3 - (1 + 2 + 3)z^2 + (1*2 + 1*3 + 2*3)z - 1*2*3 = z^3 - 6z^2 + 11z - 6. Note that this example is n=3 odd, but n=4 would have taken too long to do by hand. Edit: Let me know if you think this would be better posted at TCS or Math Stack Exchange.

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  • Active Directory Password Policy Problem

    - by Will
    To Clarify: my question is why isn't my password policy applying to people in the domain. Hey guys, having trouble with our password policy in Active Directory. Sometimes it just helps me to type out what I’m seeing It appears to not be applying properly across the board. I am new to this environment and AD in general but I think I have a general grasp of what should be going on. It’s a pretty simple AD setup without too many Group Policies being applied. It looks something like this DOMAIN Default Domain Policy (link enabled) Password Policy (link enabled and enforce) Personal OU Force Password Change (completely empty nothing in this GPO) IT OU Lockout Policy (link enabled and enforced) CS OU Lockout Policy Accouting OU Lockout Policy The password policy and default domain policy both define the same things under Computer ConfigWindows seetings sec settings Account Policies / Password Policy Enforce password History : 24 passwords remembered Maximum Password age : 180 days Min password age: 14 days Minimum Password Length: 6 characters Password must meet complexity requirements: Enabled Store Passwords using reversible encryption: Disabled Account Policies / Account Lockout Policy Account Lockout Duration 10080 Minutes Account Lockout Threshold: 5 invalid login attempts Reset Account Lockout Counter after : 30 minutes IT lockout This just sets the screen saver settings to lock computers when the user is Idle. After running Group Policy modeling it seems like the password policy and default domain policy is getting applied to everyone. Here is the results of group policy modeling on MO-BLANCKM using the mblanck account, as you can see the policies are both being applied , with nothing important being denied Group Policy Results NCLGS\mblanck on NCLGS\MO-BLANCKM Data collected on: 12/29/2010 11:29:44 AM Summary Computer Configuration Summary General Computer name NCLGS\MO-BLANCKM Domain NCLGS.local Site Default-First-Site-Name Last time Group Policy was processed 12/29/2010 10:17:58 AM Group Policy Objects Applied GPOs Name Link Location Revision Default Domain Policy NCLGS.local AD (15), Sysvol (15) WSUS-52010 NCLGS.local/WSUS/Clients AD (54), Sysvol (54) Password Policy NCLGS.local AD (58), Sysvol (58) Denied GPOs Name Link Location Reason Denied Local Group Policy Local Empty Security Group Membership when Group Policy was applied BUILTIN\Administrators Everyone S-1-5-21-507921405-1326574676-682003330-1003 BUILTIN\Users NT AUTHORITY\NETWORK NT AUTHORITY\Authenticated Users NCLGS\MO-BLANCKM$ NCLGS\Admin-ComputerAccounts-GP NCLGS\Domain Computers WMI Filters Name Value Reference GPO(s) None Component Status Component Name Status Last Process Time Group Policy Infrastructure Success 12/29/2010 10:17:59 AM EFS recovery Success (no data) 10/28/2010 9:10:34 AM Registry Success 10/28/2010 9:10:32 AM Security Success 10/28/2010 9:10:34 AM User Configuration Summary General User name NCLGS\mblanck Domain NCLGS.local Last time Group Policy was processed 12/29/2010 11:28:56 AM Group Policy Objects Applied GPOs Name Link Location Revision Default Domain Policy NCLGS.local AD (7), Sysvol (7) IT-Lockout NCLGS.local/Personal/CS AD (11), Sysvol (11) Password Policy NCLGS.local AD (5), Sysvol (5) Denied GPOs Name Link Location Reason Denied Local Group Policy Local Empty Force Password Change NCLGS.local/Personal Empty Security Group Membership when Group Policy was applied NCLGS\Domain Users Everyone BUILTIN\Administrators BUILTIN\Users NT AUTHORITY\INTERACTIVE NT AUTHORITY\Authenticated Users LOCAL NCLGS\MissingSkidEmail NCLGS\Customer_Service NCLGS\Email_Archive NCLGS\Job Ticket Users NCLGS\Office Staff NCLGS\CUSTOMER SERVI-1 NCLGS\Prestige_Jobs_Email NCLGS\Telecommuters NCLGS\Everyone - NCL WMI Filters Name Value Reference GPO(s) None Component Status Component Name Status Last Process Time Group Policy Infrastructure Success 12/29/2010 11:28:56 AM Registry Success 12/20/2010 12:05:51 PM Scripts Success 10/13/2010 10:38:40 AM Computer Configuration Windows Settings Security Settings Account Policies/Password Policy Policy Setting Winning GPO Enforce password history 24 passwords remembered Password Policy Maximum password age 180 days Password Policy Minimum password age 14 days Password Policy Minimum password length 6 characters Password Policy Password must meet complexity requirements Enabled Password Policy Store passwords using reversible encryption Disabled Password Policy Account Policies/Account Lockout Policy Policy Setting Winning GPO Account lockout duration 10080 minutes Password Policy Account lockout threshold 5 invalid logon attempts Password Policy Reset account lockout counter after 30 minutes Password Policy Local Policies/Security Options Network Security Policy Setting Winning GPO Network security: Force logoff when logon hours expire Enabled Default Domain Policy Public Key Policies/Autoenrollment Settings Policy Setting Winning GPO Enroll certificates automatically Enabled [Default setting] Renew expired certificates, update pending certificates, and remove revoked certificates Disabled Update certificates that use certificate templates Disabled Public Key Policies/Encrypting File System Properties Winning GPO [Default setting] Policy Setting Allow users to encrypt files using Encrypting File System (EFS) Enabled Certificates Issued To Issued By Expiration Date Intended Purposes Winning GPO SBurns SBurns 12/13/2007 5:24:30 PM File Recovery Default Domain Policy For additional information about individual settings, launch Group Policy Object Editor. Public Key Policies/Trusted Root Certification Authorities Properties Winning GPO [Default setting] Policy Setting Allow users to select new root certification authorities (CAs) to trust Enabled Client computers can trust the following certificate stores Third-Party Root Certification Authorities and Enterprise Root Certification Authorities To perform certificate-based authentication of users and computers, CAs must meet the following criteria Registered in Active Directory only Administrative Templates Windows Components/Windows Update Policy Setting Winning GPO Allow Automatic Updates immediate installation Enabled WSUS-52010 Allow non-administrators to receive update notifications Enabled WSUS-52010 Automatic Updates detection frequency Enabled WSUS-52010 Check for updates at the following interval (hours): 1 Policy Setting Winning GPO Configure Automatic Updates Enabled WSUS-52010 Configure automatic updating: 4 - Auto download and schedule the install The following settings are only required and applicable if 4 is selected. Scheduled install day: 0 - Every day Scheduled install time: 03:00 Policy Setting Winning GPO No auto-restart with logged on users for scheduled automatic updates installations Disabled WSUS-52010 Re-prompt for restart with scheduled installations Enabled WSUS-52010 Wait the following period before prompting again with a scheduled restart (minutes): 30 Policy Setting Winning GPO Reschedule Automatic Updates scheduled installations Enabled WSUS-52010 Wait after system startup (minutes): 1 Policy Setting Winning GPO Specify intranet Microsoft update service location Enabled WSUS-52010 Set the intranet update service for detecting updates: http://lavender Set the intranet statistics server: http://lavender (example: http://IntranetUpd01) User Configuration Administrative Templates Control Panel/Display Policy Setting Winning GPO Hide Screen Saver tab Enabled IT-Lockout Password protect the screen saver Enabled IT-Lockout Screen Saver Enabled IT-Lockout Screen Saver executable name Enabled IT-Lockout Screen Saver executable name sstext3d.scr Policy Setting Winning GPO Screen Saver timeout Enabled IT-Lockout Number of seconds to wait to enable the Screen Saver Seconds: 1800 System/Power Management Policy Setting Winning GPO Prompt for password on resume from hibernate / suspend Enabled IT-Lockout

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  • Is there a way to delay compilation of a stored procedure's execution plan?

    - by Ian Henry
    (At first glance this may look like a duplicate of http://stackoverflow.com/questions/421275 or http://stackoverflow.com/questions/414336, but my actual question is a bit different) Alright, this one's had me stumped for a few hours. My example here is ridiculously abstracted, so I doubt it will be possible to recreate locally, but it provides context for my question (Also, I'm running SQL Server 2005). I have a stored procedure with basically two steps, constructing a temp table, populating it with very few rows, and then querying a very large table joining against that temp table. It has multiple parameters, but the most relevant is a datetime "@MinDate." Essentially: create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @MinDate If I just execute this as a normal query, by declaring @MinDate as a local variable and running that, it produces an optimal execution plan that executes very quickly (first joins on #smallTable and then only considers a very small subset of rows from aGiantTable while doing other operations). It seems to realize that #smallTable is tiny, so it would be efficient to start with it. This is good. However, if I make that a stored procedure with @MinDate as a parameter, it produces a completely inefficient execution plan. (I am recompiling it each time, so it's not a bad cached plan...at least, I sure hope it's not) But here's where it gets weird. If I change the proc to the following: declare @LocalMinDate datetime set @LocalMinDate = @MinDate --where @MinDate is still a parameter create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @LocalMinDate Then it gives me the efficient plan! So my theory is this: when executing as a plain query (not as a stored procedure), it waits to construct the execution plan for the expensive query until the last minute, so the query optimizer knows that #smallTable is small and uses that information to give the efficient plan. But when executing as a stored procedure, it creates the entire execution plan at once, thus it can't use this bit of information to optimize the plan. But why does using the locally declared variables change this? Why does that delay the creation of the execution plan? Is that actually what's happening? If so, is there a way to force delayed compilation (if that indeed is what's going on here) even when not using local variables in this way? More generally, does anyone have sources on when the execution plan is created for each step of a stored procedure? Googling hasn't provided any helpful information, but I don't think I'm looking for the right thing. Or is my theory just completely unfounded? Edit: Since posting, I've learned of parameter sniffing, and I assume this is what's causing the execution plan to compile prematurely (unless stored procedures indeed compile all at once), so my question remains -- can you force the delay? Or disable the sniffing entirely? The question is academic, since I can force a more efficient plan by replacing the select * from aGiantTable with select * from (select * from aGiantTable where ID in (select ID from #smallTable)) as aGiantTable Or just sucking it up and masking the parameters, but still, this inconsistency has me pretty curious.

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