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• Possible applications of algorithm devised for differentiating between structured vs random text

  - by rooznom

  I have written a program that can rapidly (within 5 sec on a 2GB RAM desktop, 2.33 Ghz CPU) differentiate between structured text (e.g english text) and random alphanumeric strings. It can also provide a probability score for the prediction. Are there any practical applications/uses of such a program. Note that the program is based on entropy models and does not have any dictionary comparisons in its workflow. Thanks in advance for your responses

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• Structuring cascading properties - parent only or parent + entire child graph?

  - by SB2055

  I have a Folder entity that can be Moderated by users. Folders can contain other folders. So I may have a structure like this: Folder 1 Folder 2 Folder 3 Folder 4 I have to decide how to implement Moderation for this entity. I've come up with two options: Option 1 When the user is given moderation privileges to Folder 1, define a moderator relationship between Folder 1 and User 1. No other relationships are added to the db. To determine if the user can moderate Folder 3, I check and see if User 1 is the moderator of any parent folders. This seems to alleviate some of the complexity of handling updates / moved entities / additions under Folder 1 after the relationship has been defined, and reverting the relationship means I only have to deal with one entity. Option 2 When the user is given moderation privileges to Folder 1, define a new relationship between User 1 and Folder 1, and all child entities down to the grandest of grandchildren when the relationship is created, and if it's ever removed, iterate back down the graph to remove the relationship. If I add something under Folder 2 after this relationship has been made, I just copy all Moderators into the new Entity. But when I need to show only the top-level Folders that a user is Moderating, I need to query all folders that have a parent folder that the user does not moderate, as opposed to option 1, where I just query any items that the user is moderating. I think it comes down to determining if users will be querying for all parent items more than they'll be querying child items... if so, then option 1 seems better. But I'm not sure. Is either approach better than the other? Why? Or is there another approach that's better than both? I'm using Entity Framework in case it matters.

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• Construct an array from an existing array

  - by Luv

  Given an array of integers A[1...n-1] where 'N' is the length of array A[ ]. Construct an array B such that B[i] = min(A[i], A[i+1], ..., A[i+K-1]), where K will be given. Array B will have N-K+1 elements. We can solve the problem using min-heaps Construct min-heap for k elements - O(k) For every next element delete the first element and insert the new element and heapify Hence Worst Case Time - O( (n-k+1)*k ) + O(k) Space - O(k) Can we do it better?

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• Logic or Algorithm to solve this problem [closed]

  - by jade

  I have two lists. List1 {a,b,c,d,e} and List2 {f,g,h,i,j} The relation between the two list is as follows a->g,a->h,h->c,h->d,d->i,d->j Now I have these two lists displayed. Based on the relation above on selecting element a from List1, List2 shows g,h. On selecting h from List2, in List1 c,d are shown in List1. On selecting d from List1 it shows i,j in List2. How to trace back to initial state by deselecting the elements in reverse order in which they have been selected?

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• What is the name of this array transformation?

  - by Brandon Tilley

  Start with an array of arrays; in this case, they are different lengths in order to demonstrate the technique, but they do not have to be. [[1,2,3,4], [5,6,7], [8,9,10], [11,12,13,14,15]] At the other end of the transformation, you have an array of arrays where the first array contains the first element from each of the original arrays, the second array contains the second element from each of the original arrays, and so on. [[1,5,8,11], [2,6,9,12], [3,7,10,13], [4,14], [15]] Is there a mathematical or CS term for this operation?

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• How to avoid oscillation by async event based systems?

  - by inf3rno

  Imagine a system where there are data sources which need to be kept in sync. A simple example is model - view data binding by MVC. Now I intend to describe these kind of systems with data sources and hubs. Data sources are publishing and subscribing for events and hubs are relaying events to data sources. By handling an event a data source will change it state described in the event. By publishing an event the data source puts its current state to the event, so other data sources can use that information to change their state accordingly. The only problem with this system, that events can be reflected from the hub or from the other data sources, and that can put the system into an infinite oscillation (by async or infinite loop by sync). For example A -- data source B -- data source H -- hub A -> H -> A -- reflection from the hub A -> H -> B -> H -> A -- reflection from another data source By sync it is relatively easy to solve this issue. You can compare the current state with the event, and if they are equal, you don't change the state and raise the same event again. By async I could not find a solution yet. The state comparison does not work by async event handling because there is eventual consistency, and new events can be published in an inconsistent state causing the same oscillation. For example: A(*->x) -> H -> B(y->x) -- can go parallel with B(*->y) -> H -> A(x->y) -- so first A changes to x state while B changes to y state -- then B changes to x state while A changes to y state -- and so on for eternity... What do you think is there an algorithm to solve this problem? If there is a solution, is it possible to extend it to prevent oscillation caused by multiple hubs, multiple different events, etc... ? update: I don't think I can make this work without a lot of effort. I think this problem is just the same as we have by syncing multiple databases in a distributed system. So I think what I really need is constraints if I want to prevent this problem in an automatic way. What constraints do you suggest?

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• Performing a Depth First Search iteratively using async/parallel processing?

  - by Prabhu

  Here is a method that does a DFS search and returns a list of all items given a top level item id. How could I modify this to take advantage of parallel processing? Currently, the call to get the sub items is made one by one for each item in the stack. It would be nice if I could get the sub items for multiple items in the stack at the same time, and populate my return list faster. How could I do this (either using async/await or TPL, or anything else) in a thread safe manner? private async Task<IList<Item>> GetItemsAsync(string topItemId) { var items = new List<Item>(); var topItem = await GetItemAsync(topItemId); Stack<Item> stack = new Stack<Item>(); stack.Push(topItem); while (stack.Count > 0) { var item = stack.Pop(); items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } } return items; } I was thinking of something along these lines, but it's not coming together: var tasks = stack.Select(async item => { items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } }).ToList(); if (tasks.Any()) await Task.WhenAll(tasks); The language I'm using is C#.

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• Find possible variations of one item out of multiple baskets.

  - by tugberk

  I have three baskets of balls and each of them has 10 balls which have the following numbers: Basket 1: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Basket 2: 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 Basket 3: 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 What would be the possible variations If I were to pick one ball from each basket? I guess this is called as Probability in Mathematics but not sure. How would you write this code in C# (or any other programming language) to get the correct results? Edit: Based on @Kilian Foth's comment, here is the solution in C#: class Program { static void Main(string[] args) { IEnumerable<string> basket1 = new List<string> { "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" }; IEnumerable<string> basket2 = new List<string> { "11", "12", "13", "14", "15", "16", "17", "18", "19", "20" }; IEnumerable<string> basket3 = new List<string> { "21", "22", "23", "24", "25", "26", "27", "28", "29", "30" }; foreach (var item1 in basket1) foreach (var item2 in basket2) foreach (var item3 in basket3) { Console.WriteLine("{0}, {1}, {2}", item1, item2, item3); } Console.ReadLine(); } }

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• Finding maximum number of congruent numbers

  - by Stefan Czarnecki

  Let's say we have a multiset (set with possible duplicates) of integers. We would like to find the size of the largest subset of the multiset such that all numbers in the subset are congruent to each other modulo some m 1. For example: 1 4 7 7 8 10 for m = 2 the subsets are: (1, 7, 7) and (4, 8, 10), both having size 3. for m = 3 the subsets are: (1, 4, 7, 7, 10) and (8), the larger set of size 5. for m = 4 the subsets are: (1), (4, 8), (7, 7), (10), the largest set of size 2. At this moment it is evident that the best answer is 5 for m = 3. Given m we can find the size of the largest subset in linear time. Because the answer is always equal or larger than half of the size of the set, it is enough to check for values of m upto median of the set. Also I noticed it is necessary to check for only prime values of m. However if values in the set are large the algorithm is still rather slow. Does anyone have any ideas how to improve it?

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• Algorithm to increase odds of matching when randomly selecting

  - by Bryan

  I am building a mobile game loosely based on dual n-back http://brainworkshop.sourceforge.net/tutorial.html Now with the game I have 9 squares (numbered 1 through 9) and 9 letters (A through K) In the current code, I randomly select a square (e.g. 3) and a letter (e.g. C), then repeat the random selection for the next turn. For 1-back, I test whether either, neither or both match the previous turn. The problem with my current code is I get very few matches - I can go through many turns without having either match. How can I increase the match frequency, or alternatively decrease the randomness so a match is more likely? I am not looking for specific code (but pseudo-code would be fine) - just more an approach to increase match frequency.

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• How to create Button/Switch-Like Tile where you can step on it and change its value?

  - by aldroid16

  If the player steps on a Button-Tile when its true, it becomes false. If the player steps on a Button-Tile when it is false, it becomes true. The problem is, when the player stands on (intersects) the Button-Tile, it will keep updating the condition. So, from true, it becomes false. Because its false and the player intersects it, it becomes true again. True-false-true-false and so on. I use ElapsedGameTime to make the updating process slower, and the player can have a chance to change the Button to true or false. However, it's not the solution I was looking for. Is there any other way to make it keep in False/True condition while the Player is standing on the Button tile?

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• Initialize array in amortized constant time -- what is this trick called?

  - by user946850

  There is this data structure that trades performance of array access against the need to iterate over it when clearing it. You keep a generation counter with each entry, and also a global generation counter. The "clear" operation increases the generation counter. On each access, you compare local vs. global generation counters; if they differ, the value is treated as "clean". This has come up in this answer on Stack Overflow recently, but I don't remember if this trick has an official name. Does it? One use case is Dijkstra's algorithm if only a tiny subset of the nodes has to be relaxed, and if this has to be done repeatedly.

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• What are the common techniques to handle user-generated HTML modified differently by different browsers?

  - by Jakie

  I am developing a website updater. The front end uses HTML, CSS and JavaScript, and the backend uses Python. The way it works is that <p/>, <b/> and some other HTML elements can be updated by the user. To enable this, I load the webpage and, with JQuery, convert all those elements to <textarea/> elements. Once they the content of the text area is changed, I apply the change to the original elements and send it to a Python script to store the new content. The problem is that I'm finding that different browsers change the original HTML. How do you get around this issue? What Python libraries do you use? What techniques or application designs do you use to avoid or overcome this issue? The problems I found are: IE removes the quotes around class and id attributes. For example, <img class='abc'/> becomes <img class=abc/>. Firefox removes the backslash from the line breaks: <br \> becomes <br>. Some websites have very specific display technicalities, so an insertion of a simple "\n"(which IE does) can affect the display of a website. Example: changing <img class='headingpic' /><div id="maincontent"> to <img class='headingpic'/>\n <div id="maincontent"> inserts a vertical gap in IE. The things I have unsuccessfully tried to overcome these issues: Using either JQuery or Python to remove all >\n< occurences, <br> etc. But this fails because I get different patterns in IE, sometimes a ·\n, sometimes a \n···. In a Python, parse the new HTML, extract the new text/content, insert it into the old HTML so the elements and format never change, just the content. This is very difficult and seems to be overkill.

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• Arranging the colors on the board in the most pleasing form

  - by Shashwat

  Given a rectangular board of height H and width W. N colors are given. ith color occupy Pi percentage of area on the board. Sum of Pis is 1. What can be algorithm to layout the colors on the board in the form of rectangles in the most pleasing form. By pleasing mean the aspect ratios (Width/Height) of rectangle of each color should be as close to 1 as possible. In an ideal case the board would be filled only with squares.

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• In Search Data Structure And Algorithm Project Title Based on Topic

  - by Salehin Suhaimi

  As the title says, my lecturer gave me a project that i needed to finish in 3 weeks before final semester exams. So i thought i will start now. The requirement is to "build a simple program that has GUI based on all the chapter that we've learned." But i got stuck on WHAT program should i build. Any idea a program that is related to this chapter i've learned? Any input will help. list, array list, linked list, vectors, stacks, Queues, ADT, Hashing, Binary Search Tree, AVL Tree, That's about all i can remember. Any idea where can i start looking?

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• Partitioning set into subsets with respect to equality of sum among subsets

  - by Al.Net

  let say i have {3, 1, 1, 2, 2, 1,5,2,7} set of numbers, I need to split the numbers such that sum of subset1 should be equal to sum of subset2 {3,2,7} {1,1,2,1,5,2}. First we should identify whether we can split number(one way might be dividable by 2 without any remainder) and if we can, we should write our algorithm two create s1 and s2 out of s. How to proceed with this approach? I read partition problem in wiki and even in some articles but i am not able to get anything. Can someone help me to find the right algorithm and its explanation in simple English?

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• reference list for non-IT driven algorithmic patterns

  - by Quicker

  I am looking for a reference list for non-IT driven algorithmic patterns (which still can be helped with IT implementations of IT). An Example List would be: name; short desc; reference Travelling Salesman; find the shortest possible route on a multiple target path; http://en.wikipedia.org/wiki/Travelling_salesman_problem Ressource Disposition (aka Regulation); Distribute a limited/exceeding input on a given number output receivers based on distribution rules; http://database-programmer.blogspot.de/2010/12/critical-analysis-of-algorithm-sproc.html If there is no such list, but you instantly think of something specific, please 'put it on the desk'. Maybe I can compile something out of the input I get here (actually I am very frustrated as I did not find any such list via research by myself). Details on Scoping: I found it very hard to formulate what I want in a way everything is out that I do not need (which may be the issue why I did not find anything at google). There is a database centric definition for what I am looking for in the section 'Processes' of the second example link. That somehow fits, but the database focus sort of drifts away from the pattern thinking, which I have in mind. So here are my own thoughts around what's in and what's out: I am NOT looking for a foundational algo ref list, which is implemented as basis for any programming language. Eg. the php reference describes substr and strlen. That implements algos, but is not what I am looking for. the problem the algo does address would even exist, if there were no computers (or other IT components) the main focus of the algo is NOT to help other algo's chances are high, that there are implementions of the solution or any workaround without any IT support out there in the world however the algo could be benefitialy implemented/fully supported by a software application = means: the problem of the algo has to be addressed anyway, but running an algo implementation with software automates the process (that is why I posted it on stackoverflow and not somewhere else) typically such algo implementations have more than one input field value and more than one output field value - which implies it could not be implemented as simple function (which is fixed to produce not more than one output value) in a normalized data model often times such algo implementation outputs span accross multiple rows (sometimes multiple tables), whereby the number of output rows depends on the input paraters and rows in the table(s) at start time - which implies that any algo implementation/procedure must interact with a database (read and/or write) I am mainly looking for patterns, not for specific implementations. Example: The Travelling Salesman assumes any coordinates, however it does not say: You need a table targets with fields x and y. - however sometimes descriptions are focussed on examples with specific implementations very much - no worries, as long as the pattern gets clear

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• How to quickly search through a very large list of strings / records on a database

  - by Giorgio

  I have the following problem: I have a database containing more than 2 million records. Each record has a string field X and I want to display a list of records for which field X contains a certain string. Each record is about 500 bytes in size. To make it more concrete: in the GUI of my application I have a text field where I can enter a string. Above the text field I have a table displaying the (first N, e.g. 100) records that match the string in the text field. When I type or delete one character in the text field, the table content must be updated on the fly. I wonder if there is an efficient way of doing this using appropriate index structures and / or caching. As explained above, I only want to display the first N items that match the query. Therefore, for N small enough, it should not be a big issue loading the matching items from the database. Besides, caching items in main memory can make retrieval faster. I think the main problem is how to find the matching items quickly, given the pattern string. Can I rely on some DBMS facilities, or do I have to build some in-memory index myself? Any ideas? EDIT I have run a first experiment. I have split the records into different text files (at most 200 records per file) and put the files in different directories (I used the content of one data field to determine the directory tree). I end up with about 50000 files in about 40000 directories. I have then run Lucene to index the files. Searching for a string with the Lucene demo program is pretty fast. Splitting and indexing took a few minutes: this is totally acceptable for me because it is a static data set that I want to query. The next step is to integrate Lucene in the main program and use the hits returned by Lucene to load the relevant records into main memory.

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• solve TOR edge node problem by using .onion proxy?

  - by rd.

  I would like to improve the TOR network, where the exit nodes are a vulnerability to concealing traffic. From my understanding, traffic to .onion sites are not decrypted by exit nodes, so therefore - in theory - a .onion site web proxy could be used to further anonymize traffic. Yes/no? perhaps you have insight into the coding and routing behind these concepts to elaborate on why this is a good/not good idea.

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• What are startups expecting when they ask you to solve a programming challenge before interviewing? [closed]

  - by Swapnil Tailor

  I have applied to couple of startups and most of them are asking to solve programming challenge before they start on the interviewing candidate. I have submitted couple of the solutions and all the time getting rejected in the initial screening. Now what I think is, they will see my coding style, algorithm and OOD concepts that I have used to solve the problem. Can you guys input more on it as what other details are taken into consideration and how can I improve my coding for getting selected. By the way, I did all my coding in either Java/Perl. EDIT I feel the biggest reason for rejection is code didn't work for couple of use cases.

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• how to avoid or minimise use of check/conditional statement?

  - by Muneeb Nasir

  I have scenario, where i got stream and i need to check for some value. if i got my any new value i have to store it in any of data structure. well it seems very easy, i can place conditional statement if-else or can use contain method of set/map to check either received is new or not. but the problem is checking will effect my application performance, in stream i'll receive hundreds for value in second, if i start checking each and every value i received than for sure it effect performance. Any body can suggest me any mechanism or algorithm that solve my issue. either by bypassing checks or atleast minimize them?

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• Finding the median of the merged array of two sorted arrays in O(logN)?

  - by user176517

  Refering to the solution present at MIT handout I have tried to figure out the solution myself but have got stuck and I believe I need help to understand the following points. In the function header used in the solution MEDIAN -SEARCH (A[1 . . l], B[1 . . m], max(1,n/2 - m), min(l, n/2)) I do not understand the last two arguments why not simply 1, l why the max and min respectively. Thanking You.

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• Is using build-in sorting considered cheating in practice tests?

  - by user10326

  I am using one of the practice online judges where a practice problem is asked and one submits the answer and gets back if it is accepted or not based on test inputs. My question is the following: In one of the practice tests, I needed to sort an array as part of the solution algorithm. If it matters the problem was: find 2 numbers in an array that add up to a specific target. As part of my algorithm I sorted the array, but to do that I used Java's quicksort and not implement sorting as part of the same method. To do that I had to do: java.util.Arrays.sort(array); Since I had to use the fully qualified name I am wondering if this is a kind of "cheating". (I mean perhaps an online judge does not expect this) Is it? In a formal interview (since these tests are practice for interview as I understand) would this be acceptable?

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• When calculating how many days between 2 dates, should you include both dates in the count, or neither, or 1?

  - by Andy

  I hope this question is alright to ask here. I am trying to make an algorithm that counts how many days between 2 dates. For example, 3/1/2012 and 3/2/2012. Whats the correct answer, or the most popular choice, and should be the one I use? So in this case, if I don't include both dates I am comparing, its 0. If I include one of them (both the start date), its 1. Lastly, if I include both, its 2. Thanks.

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• Conventions for search result scoring

  - by DeaconDesperado

  I assume this type of question is more on-topic here than on regular SO. I have been working on a search feature for my team's web application and have had a lot of success building a multithreaded, "divide and conquer" processing system to work through a large amount of fulltext. Our problem domain is pretty specific. Users of the app generate posts, and as a general rule, posts that are more recent are considered to be of greater relevance. Some of the data we are trying to extract from search is very specific (user's feelings about specific items or things) and we are using python nltk to do named-entity extraction to find interesting likely query terms. Essentially we look for descriptive adjective-noun pairs and generate a general picture of a user's expressed sentiment as a list of tokens. This search is intended as an internal tool for our team to draw out a local picture of sentiments like "soggy pizza." There's some machine learning in there too to do entity resolution on terms like "soggy" to all manner of adjectives expressing nastiness. My problem is I am at a loss for how to go about scoring these results. The text being searched is split up into tokens in a list, so my initial approach would be to normalize a float score between 0.0-1.0 generated off of how far into the list the terms appear and how often they are repeated (a later mention of the term being worth less, earlier more, greater frequency-greater score, etc.) A certain amount of weight could be given to the timestamp as well, though I am not certain how to calculate this. I am curious if anyone has had to solve a similar problem in a search relevance grading between appreciable metrics (frequency, term location/colocation, recency) and if there are and guidelines for how to weight each. I should mention as well that the final fallback procedure in the search is to pipe the query to Sphinx, which has its own scoring practices. Sphinx operates as the last resort in case our application specific processing can't find any eligible candidates.

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