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• Javascript: Safely upload a client data file

  - by Jeffrey Sweeney

  I'm (still) working on a template-based XML editing program. It's a GUI-based XML editor that only allows users to add certain tags and attributes based off the requirements. You can see the current version here for an idea. Now, I'd like to allow users to upload their own data templates, but I'm concerned about potential XSS hacks. Currently, the template file is in Javascript object literal notation, which unsurprisingly is a security nightmare if the user can upload their own. I was thinking of using XML instead, but is there an even better alternative?

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• Which design better when use foreign key instead of a string to store a list of id

  - by Kien Thanh

  I'm building online examination system. I have designed to table, Question and GeneralExam. The table GeneralExam contains info about the exam like name, description, duration,... Now I would like to design table GeneralQuestion, it will contain the ids of questions belongs to a general exam. Currently, I have two ideas to design GeneralQuestion table: It will have two columns: general_exam_id, question_id. It will have two columns: general_exam_id, list_question_ids (string/text). I would like to know which designing is better, or pros and cons of each designing. I'm using Postgresql database.

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• How do I express subtle relationships in my data?

  - by Chuck H

  "A" is related to "B" and "C". How do I show that "B" and "C" might, by this context, be related as well? Example: Here are a few headlines about a recent Broadway play: 1 - David Mamet's Glengarry Glen Ross, Starring Al Pacino, Opens on Broadway 2 - Al Pacino in 'Glengarry Glen Ross': What did the critics think? 3 - Al Pacino earns lackluster reviews for Broadway turn 4 - Theater Review: Glengarry Glen Ross Is Selling Its Stars Hard 5 - Glengarry Glen Ross; Hey, Who Killed the Klieg Lights? Problem: Running a fuzzy-string match over these records will establish some relationships, but not others, even though a human reader could pick them out from context in much larger datasets. How do I find the relationship that suggests #3 is related to #4? Both of them can be easily connected to #1, but not to each other. Is there a (Googlable) name for this kind of data or structure? What kind of algorithm am I looking for? Goal: Given 1,000 headlines, a system that automatically suggests that these 5 items are all probably about the same thing. To be honest, it's been so long since I've programmed I'm at a loss how to properly articulate this problem. (I don't know what I don't know, if that makes sense). This is a personal project and I'm writing it in Python. Thanks in advance for any help, advice, and pointers!

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• queues in linux tcp stack

  - by poly

  I'm trying to understand the Linux kernel tcp_input/tcp_output and I'm lost. who create/control the queues, if the input is a thread and the out is another thread, who owns the queues in the TCP stack as there are many, I already asked about the retransmission queue before in this site, so the question would be who create this queue I know that this queue holds all sent packet to be retransmitted/deleted after ack later

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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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• Equivalent of #map in ruby in golang

  - by Oct

  I'm playing with Go and run into something I'm unable to find in Google, although there is certainly something that exists: I'm using the following struct: type Syntax struct { name string extensions *regexp.Regexp } type Scanner struct { classifier * bayesian.Classifier save_file string name_to_syntax map[string] *Syntax extensions_to_syntax map[*regexp.Regexp] *Syntax } I'd like to perform the following using Go and I'm quoting ruby because it's how I'd do that using ruby: test_regexpes = my_scanner.extensions_to_syntax.keys My goal is to get an array of *regexp.Regexp . Any idea on how to do that in a simple way ? Thank you !

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• How should I architect my Model and Data Access layer objects in my website?

  - by Robin Winslow

  I've been tasked with designing Data layer for a website at work, and I am very interested in architecture of code for the best flexibility, maintainability and readability. I am generally acutely aware of the value in completely separating out my actual Models from the Data Access layer, so that the Models are completely naive when it comes to Data Access. And in this case it's particularly useful to do this as the Models may be built from the Database or may be built from a Soap web service. So it seems to me to make sense to have Factories in my data access layer which create Model objects. So here's what I have so far (in my made-up pseudocode): class DataAccess.ProductsFromXml extends DataAccess.ProductFactory {} class DataAccess.ProductsFromDatabase extends DataAccess.ProductFactory {} These then get used in the controller in a fashion similar to the following: var xmlProductCreator = DataAccess.ProductsFromXml(xmlDataProvider); var databaseProductCreator = DataAccess.ProductsFromXml(xmlDataProvider); // Returns array of Product model objects var XmlProducts = databaseProductCreator.Products(); // Returns array of Product model objects var DbProducts = xmlProductCreator.Products(); So my question is, is this a good structure for my Data Access layer? Is it a good idea to use a Factory for building my Model objects from the data? Do you think I've misunderstood something? And are there any general patterns I should read up on for how to write my data access objects to create my Model objects?

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• How can an SQL relational database be used to model a thesaurus? [closed]

  - by Miles O'Keefe

  I would like to design a web app that functions as a simple thesaurus: a long list of words with attributes, all of which are linked to each other. This thesaurus data model can be defined as: a controlled vocabulary arranged in a known order in which equivalence, hierarchical, and associative relationships among terms are clearly displayed and identified by standardized relationship indicators. My idea so far is to have one database in which every word is a table, and every table contains all words related to that word. e.g. Thesaurus(database) - happy(table) - excited(row)|cheerful(row)|lively(row) Is there are more efficient way to store words and their relationship to other words in a relational SQL database?

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• Can anyone explain to me what problem Core Data solves?

  - by Curtis Sumpter

  Core Data seems to add a needless layer of complexity. If you want to save data created natively by the user in an app why not just use an object and then write the data all to SQLite or back to a server using a RESTful script if necessary. Android doesn't have Core Data (though if it has something similar I haven't seen it.). What the heck is the point of buggy CD except useless needless overhead for people who can't write SQL or CGI scripts?

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• Is it possible to efficiently store all possible phone numbers in memory?

  - by Spencer K

  Given the standard North American phone number format: (Area Code) Exchange - Subscriber, the set of possible numbers is about 6 billion. However, efficiently breaking down the nodes into the sections listed above would yield less than 12000 distinct nodes that can be arranged in groupings to get all the possible numbers. This seems like a problem already solved. Would it done via a graph or tree?

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• Card deck and sparse matrix interview questions

  - by MrDatabase

  I just had a technical phone screen w/ a start-up. Here's the technical questions I was asked ... and my answers. What do think of these answers? Feel free to post better answers :-) Question 1: how would you represent a standard 52 card deck in (basically any language)? How would you shuffle the deck? Answer: use an array containing a "Card" struct or class. Each instance of card has some unique identifier... either it's position in the array or a unique integer member variable in the range [0, 51]. Shuffle the cards by traversing the array once from index zero to index 51. Randomly swap ith card with "another card" (I didn't remember how this shuffle algorithm works exactly). Watch out for using the same probability for each card... that's a gotcha in this algorithm. I mentioned the algorithm is from Programming Pearls. Question 2: how to represent a large sparse matrix? the matrix can be very large... like 1000x1000... but only a relatively small number (~20) of the entries are non-zero. Answer: condense the array into a list of the non-zero entries. for a given entry (i,j) in the array... "map" (i,j) to a single integer k... then use k as a key into a dictionary or hashtable. For the 1000x1000 sparse array map (i,j) to k using something like f(i, j) = i + j * 1001. 1001 is just one plus the maximum of all i and j. I didn't recall exactly how this mapping worked... but the interviewer got the idea (I think). Are these good answers? I'm wondering because after I finished the second question the interviewer said the dreaded "well that's all the questions I have for now." Cheers!

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• Single Key Multiple Values Data Structure for one to many mapping

  - by nijhawan.saurabh

  Dictionaries are good, they are great to store Key / Value pairs but what if you want to store multiple values for a single key? Dictionaries would not allow duplicate keys. I came across a nice way to represent such a Data Structure using one of the Extension Method (ToLookup) present in System.Linq Namespace which converts an IEnumerable<T> to an ILookup<TKey, TElement>.   Now, there are two parameters this method expects (The other overload expects 3 parameters): IEnumerable<TSource> - This list would contain the actual data. Func<TSource, TKey> keySelector - The Delegate which which computes the keys   The method returns the following: ILookup<TKey, TElement>   This DS would store Keys and multiple values along those keys.   Let's see a small example:        12  using System;    13     using System.Collections.Generic;    14     using System.Linq;    15     16     /// <summary>    17     /// </summary>    18     internal class Program    19     {    20         #region Methods    21     22         /// <summary>    23         /// </summary>    24         /// <param name="args">    25         /// The args.    26         /// </param>    27         private static void Main(string[] args)    28         {    29             // Create an array of strings.    30             var list = new List<string> { "IceCream1", "Chocolate Moose", "IceCream2" };    31     32             // Generate a lookup Data Structure    33             ILookup<int, string> lookupDs = list.ToLookup(item => item.Length);    34     35           // Enumerate groupings.    36             foreach (var group in lookupDs)    37             {    38                 foreach (string element in group)    39                 {    40                     Console.WriteLine(element);    41                 }    42             }    43         } Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

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• Generating Deep Arrays: Shallow to Deep, Deep to Shallow or Bad idea?

  - by MobyD

  I'm working on an array structure that will be used as the data source for a report template in a web app. The data comes from relatively complex SQL queries that return one or many rows as one dimensional associative arrays. In the case of many, they are turned into two dimensional indexed array. The data is complex and in some cases there is a lot of it. To save trips to the database (which are extremely expensive in this scenario) I'm attempting to get all of the basic arrays (1 and 2 dimension raw database data) and put them, conditionally, into a single, five level deep array. Organizing the data in PHP seems like a better idea than by using where statements in the SQL. Array Structure Array of years( year => array of types( types => array of information( total => value, table => array of data( index => db array ) ) ) ) My first question is, is this a bad idea. Are arrays like this appropriate for this situation? If this would work, how should I go about populating it? My initial thought was shallow to deep, but the more I work on this, the more I realize that it'd be very difficult to abstract out the conditionals that determine where each item goes in the array. So it seems that starting from the most deeply nested data may be the approach I should take. If this is array abuse, what alternatives exist?

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• Best approach to accessing multiple data source in a web application

  - by ced

  I've a base web application developed with .net technologies (asp.net) used into our LAN by 30 users simultanousley. From this web application I've developed two verticalization used from online users. In future i expect hundreds users simultanousley. Our company has different locations. Each site use its own database. The web application needs to retrieve information from all existing databases. Currently there are 3 database, but it's not excluded in the future expansion of new offices. My question then is: What is the best strategy for a web application to retrieve information from different databases (which have the same schema) whereas the main objective performance data access and high fault tolerance? There are case studies in the literature that I can take as an example? Do you know some good documents to study? Do you have any tips to implement this task so efficient? Intuitively I would say that two possible strategy are: perform queries from different sources in real time and aggregate data on the fly; create a repository that contains the union of the entities of interest and perform queries directly on repository;

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• Java Alphabetize Algorithm Insertion sort vs Bubble Sort

  - by Chris Okyen

  I am supposed to "Develop a program that alphabetizes three strings. The program should allow the user to enter the three strings, and then display the strings in alphabetical order." It's instructed that I need to use the String library compareTo()/charAt()/toLowerCase() to make all the characters lowercase so the Lexicon comparison is also a alphabetical comparison. Input Pseudo Code: String input[3]; Scanner keyboard = new Scanner(System.in); System.out.println("Enter three strings: "); for(byte i = 0; i < 3; i++) input[i] = keyboard.next() The sorting would be Insertion Sort: 321 2 3 1 2 31 231 1 23 1 2 3 1 23 1 23 123 Bubble Sort 321 231 213 123 Which would be more efficient in this case? The bubble sort seems to be more efficient though they seem to have equal stats for worst best and avg case, but I read the Insertion Sort is quicker for small amounts of data like my case.

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• Why does Clang/LLVM warn me about using default in a switch statement where all enumerated cases are covered?

  - by Thomas Catterall

  Consider the following enum and switch statement: typedef enum { MaskValueUno, MaskValueDos } testingMask; void myFunction(testingMask theMask) { switch theMask { case MaskValueUno: {}// deal with it case MaskValueDos: {}// deal with it default: {} //deal with an unexpected or uninitialized value } }; I'm an Objective-C programmer, but I've written this in pure C for a wider audience. Clang/LLVM 4.1 with -Weverything warns me at the default line: Default label in switch which covers all enumeration values Now, I can sort of see why this is there: in a perfect world, the only values entering in the argument theMask would be in the enum, so no default is necessary. But what if some hack comes along and throws an uninitialized int into my beautiful function? My function will be provided as a drop in library, and I have no control over what could go in there. Using default is a very neat way of handling this. Why do the LLVM gods deem this behaviour unworthy of their infernal device? Should I be preceding this by an if statement to check the argument?

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• What is the usage of Spaly Trees in the real world?

  - by Meena

  I decided to learn about Balance search trees, so I picked 2-3-4 and splay trees. I'm wondering what are the examples of splay trees usage in the real world? In this Cornell: http://www.cs.cornell.edu/courses/cs3110/2009fa/recitations/rec-splay.html I read that splay trees are 'A good example is a network router'. But from rest of the explanation seams like network routers use hash tables and not splay trees since the lookup time is constant instead of O(log n). thanks!

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• Is `break` and `continue` bad programming practice?

  - by Mikhail

  My boss keeps mentioning nonchalantly that bad programmers use break and continue in loops. I use them all the time because they make sense; let me show you the inspiration: function verify(object) { if (object->value < 0) return false; if (object->value > object->max_value) return false; if (object->name == "") return false; ... } The point here is that first the function checks that the conditions are correct, then executes the actual functionality. IMO same applies with loops: while (primary_condition) { if (loop_count > 1000) break; if (time_exect > 3600) break; if (this->data == "undefined") continue; if (this->skip == true) continue; ... } I think this makes it easier to read & debug; but I also don't see a downside. Please comment.

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• What is the name of this tree?

  - by Daniel

  It has a single root and each node has 0..N ordered sub-nodes . The keys represent a distinct set of paths. Two trees can only be merged if they share a common root. It needs to support, at minimum: insert, merge, enumerate paths. For this tree: The +-------+----------------+ | | | cat cow dog + +--------+ + | | | | drinks jumps moos barks + | milk the paths would be: The cat drinks milk The cow jumps The cow moos The dog barks It's a bit like a trie. What is it?

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• UPOS RFIDScanner data format

  - by Robert Snyder

  A lot of work that I do currently is based in the OPOS/UPOS world. My company has a device that can read 13.56Mhz tags (RFID), Smart Cards, and Mag Stripe cards. Up until somewhat recently I have only been working with RFID for a very specific scenario. That was to read UltraLight C and Desfire cards. These cards were all setup very specifically so that I could take the data read from those cards and force it into a MSR track2 format. The past couple of weeks, however, I have been working on reading RFID credit cards (since I have a Visa card I've been using mine), and Smart Card credit cards. (The visa card I have has both) In learning how to communicate with SmartCard and reading ISO7816 and EMVCO documents I became a little more familiar with how info is stored. But now I have a question regarding UPOS. The RFID data on my Visa is stored (and read) very similar to how the data is stored and read from the Smart Card on my Visa. Cool. Well in the UPOS spec for SmartCardRW the ReadData method returns a byte array. That's cool, I can just return all that data and then parse it as my heart desires. The RFID though has a LinkedList of Tags. Well this makes sense in terms of my Visa card (reminds me of a question I have in regards to SmartCard, but that is for another question) but what about ULC and Desfire, or for that matter any Mifare card. Pages, Files, Purses don't exactly fit the Tag profile. For instance lets just say I read pages 4-12 on my ULC card. Each page I read is 4 bytes long. Does this mean I have 9 tags in my LinkedList? Is my Tag id the page number? Or then how does that translate to Desfire? I open application 123456 and read file 1 and file 2, Do I have 2 tags? and if so what is my tag id? At least with my Visa I think that I have to use the Tag id (ex 5F24 for my expiration date) and value of {0x15, 0x10, 0x31} Part of me says yes..that makes sense. Another part of me says, "well if that is the case then why doesn't SmartCardRW have Tags?" So that is my question. How do I format my data from those different types of media? or is that the job of my Control Object (the application)? Is so how does it know? The only protocols I have are: // Summary: // Enumerates the available predefined RFID tag protocols the device supports. [Flags] public enum RFIDProtocols { EpcClass0 = 1, RFIDSdt0Plus = 2, EpcClass1 = 4, EpcClass1Gen2 = 8, EpcClass2 = 16, Iso14443A = 4096, Iso14443B = 8192, Iso15693 = 12288, Iso180006B = 16384, Other = 16777216, All = 1073741824, } If I use that well all of my cards that I have are all Iso14443A. I use the ATQA and the SAK to know what type of card I really have. There is no RFID property that lets me specify that. So I'm lost.

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• Analyzing Memory Usage: Java vs C++ Negligible?

  - by Anthony

  How does the memory usage of an integer object written in Java compare\contrast with the memory usage of a integer object written in C++? Is the difference negligible? No difference? A big difference? I'm guessing it's the same because an int is an int regardless of the language (?) The reason why I asked this is because I was reading about the importance of knowing when a program's memory requirements will prevent the programmer from solving a given problem. What fascinated me is the amount of memory required for creating a single Java object. Take for example, an integer object. Correct me if I'm wrong but a Java integer object requires 24 bytes of memory: 4 bytes for its int instance variable 16 bytes of overhead (reference to the object's class, garbage collection info & synchronization info) 4 bytes of padding As another example, a Java array (which is implemented as an object) requires 48+bytes: 24 bytes of header info 16 bytes of object overhead 4 bytes for length 4 bytes for padding plus the memory needed to store the values How do these memory usages compare with the same code written in C++? I used to be oblivious about the memory usage of the C++ and Java programs I wrote, but now that I'm beginning to learn about algorithms, I'm having a greater appreciation for the computer's resources.

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• Ideal data structure/techniques for storing generic scheduler data in C#

  - by GraemeMiller

  I am trying to implement a generic scheduler object in C# 4 which will output a table in HTML. Basic aim is to show some object along with various attributes, and whether it was doing something in a given time period. The scheduler will output a table displaying the headers: Detail Field 1 ....N| Date1.........N I want to initialise the table with a start date and an end date to create the date range (ideally could also do other time periods e.g. hours but that isn't vital). I then want to provide a generic object which will have associated events. Where an object has events within the period I want a table cell to be marked E.g. Name Height Weight 1/1/2011 2/1/2011 3/1/20011...... 31/1/2011 Ben 5.11 75 X X X Bill 5.7 83 X X So I created scheduler with Start Date=1/1/2011 and end date 31/1/2011 I'd like to give it my person object (already sorted) and tell it which fields I want displayed (Name, Height, Weight) Each person has events which have a start date and end date. Some events will start and end outwith but they should still be shown on the relevant date etc. Ideally I'd like to have been able to provide it with say a class booking object as well. So I'm trying to keep it generic. I have seen Javasript implementations etc of similar. What would a good data structure be for this? Any thoughts on techniques I could use to make it generic. I am not great with generics so any tips appreciated.

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• Microsoft Interview Preparation

  - by Manish

  I have 8 years of java background. Need help in identifying topics I need to prepare for Microsoft interview. I need to know how many rounds Microsoft will have and what all things these rounds consist of. I have identified the following topics. Please let me know if I need to prepare anything else as well. Arrays Linked Lists Recursion Stacks Queue Trees Graph -- What all I should prepare here Dynamic Programming -- again what all I need to prepare Sorting, Searching String Algos

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• Can JSON be made easily and safely editable by the non-technical Excel crowd?

  - by glitch

  I'm looking for a data storage format that's very intuitive and easy to edit. It should be ideally targeted towards the same crowd as Excel. At the same time I would like the data structure to be a tree. Ideally this would be JSON, since it offers both the tree aspect and allows for more interesting constructs like arrays. That and parsing libraries for JSON are ubiquitous, so I don't have to reinvent the wheel. The problem is that, at least with a non-specialized text editor, JSON is a giant pain to edit for a non-technical user. I'm thinking along the lines of someone who might have used Excel in the past, but never a real text editor. Someone who might not be comfortable with the idea of preserving JSON syntax by hand. Are there data formats out there that would fit this profile? I'd very much prefer this to be a JSON actually, but then it would require a solid editing tool that would hide the underlying implementation from the user. Think Excel and how it abstracts CSV syntax from the user. The reason I'm looking for something like this is because the team has been working with pretty hierarchical data for a while now and we've hit the limits of how easy it is to represent in simple CSVs without having to create complex rules for how represent hierarchy semantics from each row. Any suggestions?

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• Create association between informations

  - by Andrea Girardi

  I deployed a project some days ago that allow to extract some medical articles using the results of a questionnaire completed by a user. For instance, if I reply on questionnaire I'm affected by Diabetes type 2 and I'm a smoker, my algorithm extracts all articles related to diabetes bubbling up all articles contains information about Diabetes type 2 and smoking. Basically we created a list of topic and, for every topic we define a kind of "guideline" that allows to extract and order informations for a user. I'm quite sure there are some better way to put on relationship two content but I was not able to find them on network. Could you suggest my a model, algorithm or paper to better understand this kind of problem and that helps me to find a faster, and more accurate way to extract information for an user?

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