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• Predicting advantages of database denormalization

  - by Janus Troelsen

  I was always taught to strive for the highest Normal Form of database normalization, and we were taught Bernstein's Synthesis algorithm to achieve 3NF. This is all very well and it feels nice to normalize your database, knowing that fields can be modified while retaining consistency. However, performance may suffer. That's why I am wondering whether there is any way to predict the speedup/slowdown when denormalizing. That way, you can build your list of FD's featuring 3NF and then denormalize as little as possible. I imagine that denormalizing too much would waste space and time, because e.g. giant blobs are duplicated or it because harder to maintain consistency because you have to update multiple fields using a transaction. Summary: Given a 3NF FD set, and a set of queries, how do I predict the speedup/slowdown of denormalization? Link to papers appreciated too.

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• Should pathfinder in A* hold closedSet and openedSet or each object should hold its sets?

  - by Patryk

  I am about to implement A* pathfinding algorithm and I wonder how should I implement this - from the point of view of architecture. I have the pathfinder as a class - I think I will instantiate only one object of this class (or maybe make it a Singleton - this is not so important). The hardest part for me is whether the closedSet and openedSet should be attached to objects that can find the path for them or should be stored in pathfinder class ? I am opened to any hints and critique whatsoever. What is the best practice considering pathfinding in terms of design ?

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• Is running "milli"-benchmarks a good idea?

  - by Konstantin Weitz

  I just came across the Caliper project and it looks very nice. Reading the introduction to microbenchmarks, one gets the feeling that the developers would not suggest to use the framework if the benchmark takes longer than a second or so. I looked at the code and it looks like a RuntimeOutOfRangeException is actually thrown if a scenario takes longer than 10s to execute. Could you explain to me what the problems are with running larger benchmarks? My motivation for using Caliper was to compare two join-algorithm implementations. Those will definitely run for quite some time and will do some disk IO, yet running the entire database would make it hard to do the comparison, because the configuration of the algorithms and the visualization of the results would be a pain.

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• How to detect two moving shapes overlapped?

  - by user1389813

  Given a list of circles with its coordinates (x and y) that are moving every second in different direction (South-East, South-West, North-East and North-West), and the circle will change direction if it hits the wall sort of like bouncing, so how do we detect if any of them collide or overlap with each other ? I am not sure if we can use some data structures like a Binary Search Tree because since all the coordinates vary every seconds, so the tree will have to re-build accordingly. Or can we use Vertical Sweep Line Algorithm each time ? Any ideas on how to do this in a efficient way ?

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• Friendly URLs: is there a max length for search engines?

  - by Olivier Pons

  People from stackoverflow have been working closely with google team to help them make the panda algorithm more efficient, so I guess they've learned a lot from the google team. Thus they may have done very clever friendly URLs to maximize the page rank. I've seen from time to time very long URLs (can't find where) in stackoverflow, but after a certain "amount" of character there were only numbers, kind of "ok passed this length, SEOs will ignore this so let's put only numbers". I've done a huge work on my framework to make very friendly URLs, and my website can come up with URLs like: http://www.mysite.fr/recherche/region/provence-alpes-cote-d-azur/departement/bouches-du-rhone/categorie-de-metiers/paramedical/ It's very long and I'm wondering if the previous URL won't be mixed with, say, this one: http://www.mysite.fr/recherche/region/provence-alpes-cote-d-azur/departement/bouches-du-rhone/categorie-de-metiers/art/

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• How will Quantum computing affect us?

  - by CiscoIPPhone

  I am interested in quantum computing, but have not studied it in depth. Things like Shor's algorithm intrigue me. My question is: If quantum computing took off in a big way (i.e. functional quantum home computers were available) how would it affect us programmers and software developers? Would we have to learn how to make use of superposition and entanglement - would it change how we write algorithms? Would more mathematical programmers be required/would we need new skills? Would it change nothing at all from our perspective (i.e. would it be abstracted)? Your opinion is welcome.

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• Convert DVD to MKV (et al) without transcoding/recompression

  - by Oli

  Like a lot of people, I have a lot of DVDs. But we also have a stupid amount of disk space and a media centre (Boxee) so the DVDs are getting less and less use. It would be nice to convert our DVDs into something more relevant to our needs. I've dabbled with DVD ripping before but whereas I'd usually transcode down to a smaller picture size with a better video compression algorithm, this takes a silly amount of time. I don't have a couple of hours available for each disk. (Sidebar: is there dedicated, Linux-friendly hardware to improve h264 encoding performance?) So I was wondering if there's anything that take the DVD filesystem, De-CSS it, and then stitch together any the VOBs that make up the main part of the film and package that up in a wrapping format like MKV. A bonus would be if it could grab the subtitles and stick them in too but that's not a requirement as Boxee can grab the subtitles online if it needs to.

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• How to achieve a Gaussian Blur effect for shadows in LWJGL/Slick2D?

  - by user46883

  I am currently trying to implement shadows into my game, and after a lot of searching in the interwebs I came to the conclusion that drawing hard edged shadows to a low resolution pass combined with a Gaussian blur effect would fit best and make a good compromise between performance and looks - even though theyre not 100% physically accurate. Now my problem is, that I dont really know how to implement the Gaussian blur part. Its not difficult to draw shadows to a low resolutions buffer image and then stretch it which makes it more smooth, but I need to add the Gaussian blur effect. I have searched a lot on that and found some approachs for GLSL, some even here, but none of them really helped it. My game is written in Java using Slick2D/LWJGL and I would appreciate any help or approaches for an algorithm or maybe even an existing library to achieve that effect. Thanks for any help in advance.

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• Unity Dash/Lens - Auto-completion based on recent search strings

  - by Anant

  Sometimes, I find myself typing the same (or quite similar) search strings inside a Unity Lens. So, I thought whether it's possible for the Lens to remember previous searches, and provide a drop-down menu of possible suggestions (based on the past) when I start typing my new query. With Lenses for sites like Wikipedia and DuckDuckGo, the search strings are getting longer, and this feature would lend a helping hand in filling out queries faster. This could be something applicable to all Lenses, with later versions allowing individual Lenses to run their own auto-completion algorithm.

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• How should I replan A*?

  - by Gregory Weir

  I've got a pathfinding boss enemy that seeks the player using the A* algorithm. It's a pretty complex environment, and I'm doing it in Flash, so the search can get a bit slow when it's searching over long distances. If the player was stationary, I could just search once, but at the moment I'm searching every frame. This takes long enough that my framerate is suffering. What's the usual solution to this? Is there a way to "replan" A* without redoing the entire search? Should I just search a little less often (every half-second or second) and accept that there will be a little inaccuracy in the path?

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• Efficient way to sort large set of numbers

  - by 7Aces

  I have to sort a set of 100000 integers as a part of a programming Q. The time limit is pretty restrictive, so I have to use the most time-efficient approach possible. My current code - #include<cstdio> #include<algorithm> using namespace std; int main() { int n,d[100000],i; for(i=0;i<n;++i) { scanf("%d",&d[i]); } sort(d,d+n); .... } Would this approach be more efiicient? int main() { int n,d[100000],i; for(i=0;i<n;++i) { scanf("%d",&d[i]); sort(d,d+i+1); } .... } What is the most efficient way to sort a large dataset? Note - Not homework...

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• A* Jump Point Search - how does pruning really work?

  - by DeadMG

  I've come across Jump Point Search, and it seems pretty sweet to me. However, I'm unsure as to how their pruning rules actually work. More specifically, in Figure 1, it states that we can immediately prune all grey neighbours as these can be reached optimally from the parent of x without ever going through node x However, this seems somewhat at odds. In the second image, node 5 could be reached by first going through node 7 and skipping x entirely through a symmetrical path- that is, 6 -> x -> 5 seems to be symmetrical to 6 -> 7 -> 5. This would be the same as how node 3 can be reached without going through x in the first image. As such, I don't understand how these two images are not entirely equivalent, and not just rotated versions of each other. Secondly, I'd like to understand how this algorithm could be generalized to a three-dimensional search volume.

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• Reverse horizontal and vertical for a HTML table

  - by porton

  There is a two-dimensional array describing a HTML table. Each element of the array consists of: the cell content rowspan colspan Every row of this two dimensional array corresponds to <td> cells of a <tr> of the table which my software should generate. I need to "reverse" the array (interchange vertical and horizontal direction). Insofar I considered algorithm based on this idea: make a rectangular matrix of the size of the table and store in every element of this matrix the corresponding index of the element of the above mentioned array. (Note that two elements of the matrix may be identical due rowspan/colspan.) Then I could use this matrix to calculate rowspan/colspan for the inverted table. But this idea seems bad for me. Any other algorithms? Note that I program in PHP.

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• Why is it impossible to produce truly random numbers?

  - by Vinoth Kumar

  I was trying to solve a hobby problem that required generating a million random numbers. But I quickly realized, it is becoming difficult to make them unique. I picked up Algorithm Design Manual to read about random number generation. It has the following paragraph that I am fully not able to understand. Unfortunately, generating random numbers looks a lot easier than it really is. Indeed, it is fundamentally impossible to produce truly random numbers on any deterministic device. Von Neumann [Neu63] said it best: “Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.” The best we can hope for are pseudo-random numbers, a stream of numbers that appear as if they were generated randomly. Why is it impossible to produce truly random numbers in any deterministic device? What does this sentence mean?

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• How does one improve one's problem-solving ability?

  - by gcc

  How can one improve one's problem-solving ability? Everyone says same thing: "a real programmer knows how to handle real problem." But they forget how they learn this ability, or where (I know in school, no one gives us any ability, of course in my opinion). If you have any idea except above ones, feel free when you give your advice solve more problems do more exercises, write code, search google then write more ... For me, my question is like "use complex/known library instead of using your own." In other words, I want your personal experience, book recommendation, webpage on problem solving. Moreover, look your problem-solving method and give us your personal ability as if it is an algorithm

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• How do I detect multiple sprite collisions when there are >10 sprites?

  - by yao jiang

  I making a small program to animate the astar algorithm. If you look at the image, there are lots of yellow cars moving around. Those can collide at any moment, could be just one or all of them could just stupidly crash into each other. How do I detect all of those collisions? How do I find out which specific car has crash into which other car? I understand that pygame has collision function, but it only detects one collision at a time and I'd have to specify which sprites. Right now I am just trying to iterate through each sprite to see if there is collision: for car1 in carlist: for car2 in carlist: collide(car1, car2); This can't be the proper way to do it, if the car list goes to a huge number, a double loop will be too slow.

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• The Excel Column Name assigment problem

  - by Peter Larsson

  Here is a generic algorithm to get the Excel column name according to it's position. By changing the @Base parameter, you can do this for any sequence according to same style as Excel. DECLARE @Value INT = 8839,         @Base TINYINT = 26   ;WITH cteSequence(Value, Delta, Quote, Base, Chr) AS (     SELECT  CAST(@Value AS INT) AS Value,             CAST(1 AS INT) AS Delta,             CAST(@Base AS INT) AS Quote,             CAST(@Base AS INT) AS Base,             CHAR(65 +(@Value - 1) % @Base) AS Chr       UNION ALL       SELECT  Value AS Value,             Quote AS Delta,             26 * Quote AS Quote,             Base AS Base,             CHAR(65 +((Value - Delta)/ Quote - 1) % Base) AS Chr     FROM    cteSequence     WHERE   CHAR(65 +((Value - Delta)/ Quote - 1) % Base) <> '@' ) SELECT  CAST(Msg AS VARCHAR(MAX)) FROM    (             SELECT        '' + Chr             FROM        cteSequence             ORDER BY    Delta DESC             FOR XML        PATH('')         ) AS x(Msg)

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• How does bing-bot( is that the right spider-name? ) and googlebot interpret 301 redirect?

  - by jbcurtin

  I've been looking for documentation on how the Microsoft and Google bots interpret 301 redirects. It seems that google-bot stores documents on a url based index system. But I haven't been able to figure out how bing works. Should I assume that they are still working towards coping everyone else and assume they use an algorithm close to google? Is it best to just forward a page to a new location via Javascript? I think this might be a blackhat trick, but how would I tell the bots that it's not? Is 301 redirect my best option and I just have to bit the bullet because said pages are no longer in existence? What other options do I have that I might not be aware of?

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• Abstract Data Type and Data Structure

  - by mark075

  It's quite difficult for me to understand these terms. I searched on google and read a little on Wikipedia but I'm still not sure. I've determined so far that: Abstract Data Type is a definition of new type, describes its properties and operations. Data Structure is an implementation of ADT. Many ADT can be implemented as the same Data Structure. If I think right, array as ADT means a collection of elements and as Data Structure, how it's stored in a memory. Stack is ADT with push, pop operations, but can we say about stack data structure if I mean I used stack implemented as an array in my algorithm? And why heap isn't ADT? It can be implemented as tree or an array.

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• Moving around/avoiding obstacles

  - by János Harsányi

  I would like to write a "game", where you can place an obstacle (red), and then the black dot tries to avoid it, and get to the green target. I'm using a very easy way to avoid it, if the black dot is close to the red, it changes its direction, and moves for a while, then it moves forward to the green point. How could I create a "smooth" path for the computer controlled "player"? Edit: Not the smoothness is the main point, but to avoid the red blocking "wall" and not to crash into it and then avoid it. How could I implement some path finding algorithm if I just have basically 3 points? (And what would it make the things much more complicated, if you could place multiple obstacles?)

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• How to credit other authors in an open source project

  - by erik

  I have a pet project that I am planning to release as open source at some point in the not-too-distant future. A couple of the files use or are mostly code that was taken from a project released under the New BSD License. While I have changed it to fit my needs and added some small stuff, the algorithm and the functionality is basically exactly the same. I want to make sure that the author of the code gets credit and that the license is not broken, but I also want to make the reader aware that this is not the code as it was orignally released. How should I approach this? Should I isolate the code as much as possible and just retain the original license? Maybe put all the files that contain foreign code in their own folder and add a readme explaining what has been added/removed? There must have been tons of projects using other open source code. What is the standard approach to this?

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• Google keeps indexing /comment/reply URL

  - by jaypabs

  With the new update of Google algorithm called Penguin, I think my site was being penalized due to webspam. But of course I don't create post which seems to be spam to Google. It is just I think how Google index my site. I found out that Google index the URL of my site like: http://www.example.com/comment/reply/3866/26556 So there are so many comment/reply URL index by Google. I have already added: Disallow: /comment/reply/ Disallow: /?q=comment/reply/ but still Google still index this URL. Any idea how to prevent Google from indexing comments?

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• Electronic circuit simulator four-way flood-filling issues

  - by AJ Weeks

  I've made an electronic circuit board simulator which has simply 3 types of tiles: wires, power sources, and inverters. Wires connect to anything they touch, other than the sides of inverters; inverters have one input side and one output side; and finally power tiles connect in a similar manner as wires. In the case of an infinite loop, caused by the output of the inverter feeding into its input, I want inverters to oscillate (quickly turn on/off). I've attempted to implement a FloodFill algorithm to spread the power throughout the grid, but seem to have gotten something wrong, as only the tiles above the power source get powered (as seen below) I've attempted to debug the program, but have had no luck thus far. My code concerning the updating of power can be seen here.

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• Wireless not working on Dell XPS 17 after installing 12.04

  - by user60622

  I (linux newbie) have a Dell XPS 17 and tried to install Ubuntu 12.04. After installation all WLAN accesspoints near are detected. But I can not connect (but I am able to connect with other computers as well as with Dell XPS 17 under windows). Outputs: iwconfig lo no wireless extensions. wlan0 IEEE 802.11bg ESSID:"LerchenPoint" Mode:Managed Frequency:2.412 GHz Access Point: 58:6D:8F:A0:2D:58 Bit Rate=1 Mb/s Tx-Power=14 dBm Retry long limit:7 RTS thr:off Fragment thr:off Power Management:off Link Quality=70/70 Signal level=-37 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:19 Missed beacon:0 eth0 no wireless extensions. sudo lshw -class network *-network description: Wireless interface product: Centrino Wireless-N 1000 vendor: Intel Corporation physical id: 0 bus info: pci@0000:04:00.0 logical name: wlan0 version: 00 serial: 00:26:c7:99:98:28 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless configuration: broadcast=yes driver=iwlwifi driverversion=3.2.0-24-generic firmware=39.31.5.1 build 35138 latency=0 link=no multicast=yes wireless=IEEE 802.11bg resources: irq:50 memory:f0400000-f0401fff *-network description: Ethernet interface product: RTL8111/8168B PCI Express Gigabit Ethernet controller vendor: Realtek Semiconductor Co., Ltd. physical id: 0 bus info: pci@0000:0a:00.0 logical name: eth0 version: 06 serial: f0:4d:a2:56:e3:94 size: 1Gbit/s capacity: 1Gbit/s width: 64 bits clock: 33MHz capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=full firmware=rtl_nic/rtl8168e-2.fw ip=192.168.0.123 latency=0 link=yes multicast=yes port=MII speed=1Gbit/s resources: irq:47 ioport:6000(size=256) memory:f0a04000-f0a04fff memory:f0a00000-f0a03fff dmesg | grep iwl [ 10.157531] iwlwifi 0000:04:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17 [ 10.157561] iwlwifi 0000:04:00.0: setting latency timer to 64 [ 10.157598] iwlwifi 0000:04:00.0: pci_resource_len = 0x00002000 [ 10.157599] iwlwifi 0000:04:00.0: pci_resource_base = ffffc90011090000 [ 10.157601] iwlwifi 0000:04:00.0: HW Revision ID = 0x0 [ 10.157731] iwlwifi 0000:04:00.0: irq 50 for MSI/MSI-X [ 10.157834] iwlwifi 0000:04:00.0: Detected Intel(R) Centrino(R) Wireless-N 1000 BGN, REV=0x6C [ 10.157976] iwlwifi 0000:04:00.0: L1 Enabled; Disabling L0S [ 10.179772] iwlwifi 0000:04:00.0: device EEPROM VER=0x15d, CALIB=0x6 [ 10.179775] iwlwifi 0000:04:00.0: Device SKU: 0X50 [ 10.179777] iwlwifi 0000:04:00.0: Valid Tx ant: 0X1, Valid Rx ant: 0X3 [ 10.179796] iwlwifi 0000:04:00.0: Tunable channels: 13 802.11bg, 0 802.11a channels [ 10.574728] iwlwifi 0000:04:00.0: loaded firmware version 39.31.5.1 build 35138 [ 10.726409] ieee80211 phy0: Selected rate control algorithm 'iwl-agn-rs' [ 19.714132] iwlwifi 0000:04:00.0: L1 Enabled; Disabling L0S [ 19.777862] iwlwifi 0000:04:00.0: L1 Enabled; Disabling L0S [ 2251.603089] iwlwifi 0000:04:00.0: PCI INT A disabled [ 2266.578350] iwlwifi 0000:04:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17 [ 2266.578399] iwlwifi 0000:04:00.0: setting latency timer to 64 [ 2266.578435] iwlwifi 0000:04:00.0: pci_resource_len = 0x00002000 [ 2266.578437] iwlwifi 0000:04:00.0: pci_resource_base = ffffc90011090000 [ 2266.578439] iwlwifi 0000:04:00.0: HW Revision ID = 0x0 [ 2266.578704] iwlwifi 0000:04:00.0: irq 50 for MSI/MSI-X [ 2266.578808] iwlwifi 0000:04:00.0: Detected Intel(R) Centrino(R) Wireless-N 1000 BGN, REV=0x6C [ 2266.578916] iwlwifi 0000:04:00.0: L1 Enabled; Disabling L0S [ 2266.600709] iwlwifi 0000:04:00.0: device EEPROM VER=0x15d, CALIB=0x6 [ 2266.600712] iwlwifi 0000:04:00.0: Device SKU: 0X50 [ 2266.600713] iwlwifi 0000:04:00.0: Valid Tx ant: 0X1, Valid Rx ant: 0X3 [ 2266.600727] iwlwifi 0000:04:00.0: Tunable channels: 13 802.11bg, 0 802.11a channels [ 2266.605978] iwlwifi 0000:04:00.0: loaded firmware version 39.31.5.1 build 35138 [ 2266.606331] ieee80211 phy0: Selected rate control algorithm 'iwl-agn-rs' [ 2266.614179] iwlwifi 0000:04:00.0: L1 Enabled; Disabling L0S [ 2266.681541] iwlwifi 0000:04:00.0: L1 Enabled; Disabling L0S Solutions I tried: rfkill list all 0: dell-wifi: Wireless LAN Soft blocked: no Hard blocked: no 2: phy0: Wireless LAN Soft blocked: no Hard blocked: no echo "options iwlwifi 11n_disable=1" | sudo tee /etc/modprobe.d/iwlwifi.conf options iwlwifi 11n_disable=1 sudo modprobe -rfv iwlwifi WARNING: All config files need .conf: /etc/modprobe.d/blacklist, it will be ignored in a future release. rmmod /lib/modules/3.2.0-24-generic/kernel/drivers/net/wireless/iwlwifi/iwlwifi.ko rmmod /lib/modules/3.2.0-24-generic/kernel/net/mac80211/mac80211.ko rmmod /lib/modules/3.2.0-24-generic/kernel/net/wireless/cfg80211.ko sudo modprobe iwlwifi WARNING: All config files need .conf: /etc/modprobe.d/blacklist, it will be ignored in a future release. replacing iwlwifi-1000-5.ucode (current driver) against iwlwifi-1000-3.ucode sudo jockey-gtk: (jockey-gtk:2493): Gtk-CRITICAL **: gtk_icon_set_render_icon_pixbuf: assertion icon_set != NULL' failed (jockey-gtk:2493): Gtk-CRITICAL **: gtk_icon_set_render_icon_pixbuf: assertion icon_set != NULL' failed nothing is listet in "Additional drivers" (german: "Zusätzliche Treiber"). gksudo gedit /etc/modprobe.d/blacklist.conf add "blacklist acer_wmi" Any help would be appreciated very much. Thanks!!

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• deciphering columnar transposition cipher

  - by Arfan M

  I am looking for an idea on how to decipher a columnar transposition cipher without knowing the key or the length of the key. When I take the cipher text as input to my algorithm I will guess the length of the key to be the factors of the length of the cipher text. I will take the first factor suppose the length was 20 letters so I will take 2*10 (2 rows and 10 columns). Now I want to arrange the cipher text in the columns and read it row wise to see if there is any word forming and match it with a dictionary if it is something sensible. If it matches the dictionary then it means it is in correct order or else I want to know how to make other combinations of the columns and read the string again row wise. Please suggest another approach that is more efficient.

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