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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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• 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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• Where would you start if you were trying to solve this PDF classification problem?

  - by burtonic

  We are crawling and downloading lots of companies' PDFs and trying to pick out the ones that are Annual Reports. Such reports can be downloaded from most companies' investor-relations pages. The PDFs are scanned and the database is populated with, among other things, the: Title Contents (full text) Page count Word count Orientation First line Using this data we are checking for the obvious phrases such as: Annual report Financial statement Quarterly report Interim report Then recording the frequency of these phrases and others. So far we have around 350,000 PDFs to scan and a training set of 4,000 documents that have been manually classified as either a report or not. We are experimenting with a number of different approaches including Bayesian classifiers and weighting the different factors available. We are building the classifier in Ruby. My question is: if you were thinking about this problem, where would you start?

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• Grid Game Algorithm

  - by 7Aces

  Problem Link - http://www.iarcs.org.in/inoi/2009/zco2009/zco2009-1a.php You have to find the path with the maximum weight, from the top-left cell to the bottom-right cell. It could've been solved with a simple Dynamic Programming approach, if it were not for the special condition - you are allowed at most one move that can be either to the left or up. How do I now approach the problem with this special case? Also, I'm looking for a time-efficient approach. Thanks!

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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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• Is the Leptonica implementation of 'Modified Median Cut' not using the median at all?

  - by TheCodeJunkie

  I'm playing around a bit with image processing and decided to read up on how color quantization worked and after a bit of reading I found the Modified Median Cut Quantization algorithm. I've been reading the code of the C implementation in Leptonica library and came across something I thought was a bit odd. Now I want to stress that I am far from an expert in this area, not am I a math-head, so I am predicting that this all comes down to me not understanding all of it and not that the implementation of the algorithm is wrong at all. The algorithm states that the vbox should be split along the lagest axis and that it should be split using the following logic The largest axis is divided by locating the bin with the median pixel (by population), selecting the longer side, and dividing in the center of that side. We could have simply put the bin with the median pixel in the shorter side, but in the early stages of subdivision, this tends to put low density clusters (that are not considered in the subdivision) in the same vbox as part of a high density cluster that will outvote it in median vbox color, even with future median-based subdivisions. The algorithm used here is particularly important in early subdivisions, and 3is useful for giving visible but low population color clusters their own vbox. This has little effect on the subdivision of high density clusters, which ultimately will have roughly equal population in their vboxes. For the sake of the argument, let's assume that we have a vbox that we are in the process of splitting and that the red axis is the largest. In the Leptonica algorithm, on line 01297, the code appears to do the following Iterate over all the possible green and blue variations of the red color For each iteration it adds to the total number of pixels (population) it's found along the red axis For each red color it sum up the population of the current red and the previous ones, thus storing an accumulated value, for each red note: when I say 'red' I mean each point along the axis that is covered by the iteration, the actual color may not be red but contains a certain amount of red So for the sake of illustration, assume we have 9 "bins" along the red axis and that they have the following populations 4 8 20 16 1 9 12 8 8 After the iteration of all red bins, the partialsum array will contain the following count for the bins mentioned above 4 12 32 48 49 58 70 78 86 And total would have a value of 86 Once that's done it's time to perform the actual median cut and for the red axis this is performed on line 01346 It iterates over bins and check they accumulated sum. And here's the part that throws me of from the description of the algorithm. It looks for the first bin that has a value that is greater than total/2 Wouldn't total/2 mean that it is looking for a bin that has a value that is greater than the average value and not the median ? The median for the above bins would be 49 The use of 43 or 49 could potentially have a huge impact on how the boxes are split, even though the algorithm then proceeds by moving to the center of the larger side of where the matched value was.. Another thing that puzzles me a bit is that the paper specified that the bin with the median value should be located, but does not mention how to proceed if there are an even number of bins.. the median would be the result of (a+b)/2 and it's not guaranteed that any of the bins contains that population count. So this is what makes me thing that there are some approximations going on that are negligible because of how the split actually takes part at the center of the larger side of the selected bin. Sorry if it got a bit long winded, but I wanted to be as thoroughas I could because it's been driving me nuts for a couple of days now ;)

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• How to find optimal path visit every node with parallel workers complicated by dynamic edge costs?

  - by Aaron Anodide

  Say you have an acyclic directed graph with weighted edges and create N workers. My goal is to calculate the optimal way those workers can traverse the entire graph in parralel. However, edge costs may change along the way. Example: A -1-> B A -2-> C B -3-> C (if A has already been visited) B -5-> C (if A has not already been visited) Does what I describe lend itself to a standard algorithmic approach, or alternately can someone suggest if I'm looking at this in an inherently flawed way (i have an intuition I might be)?

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• Algorithm for optimal combination of two variables

  - by AlanChavez

  I'm looking for an algorithm that would be able to determine the optimal combination of two variables, but I'm not sure where to start looking. For example, if I have 10,000 rows in a database and each row contains price, and square feet is there any algorithm out there that will be able to determine what combination of price and sq ft is optimal. I know this is vague, but I assume is along the lines of Fuzzy logic and fuzzy sets, but I'm not sure and I'd like to start digging in the right field to see if I can come up with something that solves my problem.

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• How should I compress a file with multiple bytes that are the same with Huffman coding?

  - by Omega

  On my great quest for compressing/decompressing files with a Java implementation of Huffman coding (http://en.wikipedia.org/wiki/Huffman_coding) for a school assignment, I am now at the point of building a list of prefix codes. Such codes are used when decompressing a file. Basically, the code is made of zeroes and ones, that are used to follow a path in a Huffman tree (left or right) for, ultimately, finding a byte. In this Wikipedia image, to reach the character m the prefix code would be 0111 The idea is that when you compress the file, you will basically convert all the bytes of the file into prefix codes instead (they tend to be smaller than 8 bits, so there's some gain). So every time the character m appears in a file (which in binary is actually 1101101), it will be replaced by 0111 (if we used the tree above). Therefore, 1101101110110111011011101101 becomes 0111011101110111 in the compressed file. I'm okay with that. But what if the following happens: In the file to be compressed there exists only one unique byte, say 1101101. There are 1000 of such byte. Technically, the prefix code of such byte would be... none, because there is no path to follow, right? I mean, there is only one unique byte anyway, so the tree has just one node. Therefore, if the prefix code is none, I would not be able to write the prefix code in the compressed file, because, well, there is nothing to write. Which brings this problem: how would I compress/decompress such file if it is impossible to write a prefix code when compressing? (using Huffman coding, due to the school assignment's rules) This tutorial seems to explain a bit better about prefix codes: http://www.cprogramming.com/tutorial/computersciencetheory/huffman.html but doesn't seem to address this issue either.

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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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• Is there a phrase or word to describe an algorithim or program is complete in that given any value for its arguments there is a defined outcome?

  - by Mrk Mnl

  Is there a phrase or word to describe an algorithim or programme is complete in that given any value for its arguments there is a defined outcome? i.e. all the ramifications have been considered whatever the context? A simple example would be the below function: function returns string get_item_type(int type_no) { if(type_no < 10) return "hockey stick" else if (type_no < 20) return "bulldozer" else return "unknown" } (excuse the dismal pseudo code) No matter what number is supplied all possibiblites are catered for. My question is: is there a word to fill the blank here: "get_item_type() is ______ complete" ? (The answer is not Turing Complete - that is something quite different - but I annoyingly always think of something as "Turing Complete" when I am thinking of the above).

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• Efficient Bus Loading

  - by System Down

  This is something I did for a bus travel company a long time ago, and I was never happy with the results. I was thinking about that old project recently and thought I'd revisit that problem. Problem: Bus travel company has several buses with different passenger capacities (e.g. 15 50-passenger buses, 25 30-passenger buses ... etc). They specialized in offering transportation to very large groups (300+ passengers per group). Since each group needs to travel together they needed to manage their fleet efficiently to reduce waste. For instance, 88 passengers are better served by three 30-passenger buses (2 empty seats) than by two 50-passenger buses (12 empty seats). Another example, 75 passengers would be better served by one 50-passenger bus and one 30-passenger bus, a mix of types. What's a good algorithm to do this?

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• Slides and Code from “Using C#’s Async Effectively”

  - by Reed

  The slides and code from my talk on the new async language features in C# and VB.Net are now available on https://github.com/ReedCopsey/Effective-Async This includes the complete slide deck, and all 4 projects, including: FakeService: Simple WCF service to run locally and simulate network service calls. AsyncService: Simple WCF service which wraps FakeService to demonstrate converting sync to async SimpleWPFExample: Simplest example of converting a method call to async from a synchronous version AsyncExamples: Windows Store application demonstrating main concepts, pitfalls, tips, and tricks from the slide deck

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• Common Substring of two strings

  - by Chander Shivdasani

  This particular interview-question stumped me: Given two Strings S1 and S2. Find the longest Substring which is a Prefix of S1 and suffix of S2. Through Google, I came across the following solution, but didnt quite understand what it was doing. public String findLongestSubstring(String s1, String s2) { List<Integer> occurs = new ArrayList<>(); for (int i = 0; i < s1.length(); i++) { if (s1.charAt(i) == s2.charAt(s2.length()-1)) { occurs.add(i); } } Collections.reverse(occurs); for(int index : occurs) { boolean equals = true; for(int i = index; i >= 0; i--) { if (s1.charAt(index-i) != s2.charAt(s2.length() - i - 1)) { equals = false; break; } } if(equals) { return s1.substring(0,index+1); } } return null; }

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• Approach to Authenticate Clients to TCP Server

  - by dab

  I'm writing a Server/Client application where clients will connect to the server. What I want to do, is make sure that the client connecting to the server is actually using my protocol and I can "trust" the data being sent from the client to the server. What I thought about doing is creating a sort of hash on the client's machine that follows a particular algorithm. What I did in a previous version was took their IP address, the client version, and a few other attributes of the client and sent it as a calculated hash to the server, who then took their IP, and the version of the protocol the client claimed to be using, and calculated that number to see if they matched. This works ok until you get clients that connect from within a router environment where their internal IP is different from their external IP. My fix for this was to pass the client's internal IP used to calculate this hash with the authentication protocol. My fear is this approach is not secure enough. Since I'm passing the data used to create the "auth hash". Here's an example of what I'm talking about: Client IP: 192.168.1.10, Version: 2.4.5.2 hash = 2*4*5*1 * (1+9+2) * (1+6+8) * (1) * (1+0) Client Connects to Server client sends: auth hash ip version Server calculates that info, and accepts or denies the hash. Before I go and come up with another algorithm to prove a client can provide data a server (or use this existing algorithm), I was wondering if there are any existing, proven, and secure systems out there for generating a hash that both sides can generate with general knowledge. The server won't know about the client until the very first connection is established. The protocol's intent is to manage a network of clients who will be contributing data to the server periodically. New clients will be added simply by connecting the client to the server and "registering" with the server. So a client connects to the server for the first time, and registers their info (mac address or some other kind of unique computer identifier), then when they connect again, the server will recognize that client as a previous person and associate them with their data in the database.

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• Writing a spell checker similar to "did you mean"

  - by user888734

  I'm hoping to write a spellchecker for search queries in a web application - not unlike Google's "Did you mean?" The algorithm will be loosely based on this: http://catalog.ldc.upenn.edu/LDC2006T13 In short, it generates correction candidates and scores them on how often they appear (along with adjacent words in the search query) in an enormous dataset of known n-grams - Google Web 1T - which contains well over 1 billion 5-grams. I'm not using the Web 1T dataset, but building my n-gram sets from my own documents - about 200k docs, and I'm estimating tens or hundreds of millions of n-grams will be generated. This kind of process is pushing the limits of my understanding of basic computing performance - can I simply load my n-grams into memory in a hashtable or dictionary when the app starts? Is the only limiting factor the amount of memory on the machine? Or am I barking up the wrong tree? Perhaps putting all my n-grams in a graph database with some sort of tree query optimisation? Could that ever be fast enough?

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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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• An algorithm for finding subset matching criteria?

  - by Macin

  I recently came up with a problem which I would like to share some thoughts about with someone on this forum. This relates to finding a subset. In reality it is more complicated, but I tried to present it here using some simpler concepts. To make things easier, I created this conceptual DB model: Let's assume this is a DB for storing recipes. Recipe can have many instructions steps and many ingredients. Ingredients are stored in a cupboard and we know how much of each ingredient we have. Now, when we create a recipe, we have to define how much of each ingredient we need. When we want to use a recipe, we would just check if required amount is less than available amount for each product and then decide if we can cook a dinner - if amount required for at least one ingredient is less than available amount - recipe cannot be cooked. Simple sql query to get the result. This is straightforward, but I'm wondering, how should I work when the problem is stated the other way round, i.e. how to find recipies which can be cooked only from ingredients that are available? I hope my explanation is clear, but if you need any more clarification, please ask.

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• Structuring Access Control In Hierarchical Object 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. Thoughts 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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• Algorithm for Learning development

  - by user9057

  Hi all, This is a fairly general question. I know a bit of Perl and Python and I am looking to learn programming in more depth so that once I get the hang of it I can start developing applications and then websites. I would like to know of an algorithm (sequence of steps :)) that could describe my approach towards learning programming in general. I have posted small questions on Perl/Python and I have recieved great help from everyone. Note:- I am not in a hurry to learn. I know it takes time and that's fine. Please give any suggestions you think are valid. Also, please don't push me to learn Lisp, Haskell etc - I am a beginner.

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• How to identify a PDF classification problem?

  - by burtonic

  We are crawling and downloading lots of companies' PDFs and trying to pick out the ones that are Annual Reports. Such reports can be downloaded from most companies' investor-relations pages. The PDFs are scanned and the database is populated with, among other things, the: Title Contents (full text) Page count Word count Orientation First line Using this data we are checking for the obvious phrases such as: Annual report Financial statement Quarterly report Interim report Then recording the frequency of these phrases and others. So far we have around 350,000 PDFs to scan and a training set of 4,000 documents that have been manually classified as either a report or not. We are experimenting with a number of different approaches including Bayesian classifiers and weighting the different factors available. We are building the classifier in Ruby. My question is: if you were thinking about this problem, where would you start?

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• Labeling algorithm for points

  - by Qwertie

  I need an algorithm to place horizontal text labels for multiple series of points on the screen (basically I need to show timestamps and other information for a history of moving objects on a map; in general there are multiple data points per object). The text labels should appear close to their points--above, below, or on the right side--but should not overlap other points or text labels. Does anyone know an algorithm/heuristic for this?

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• Photo sharing social platform [closed]

  - by user1696497

  I am working on a photo sharing social platform like Flickr, Photobucket. To start off with I have half a million photos as of now. I want to convert all of these into a single format, compression ratio and use it as an original image. I will be storing original image, re-sized image according to layout and a thumbnail. I have started off with ruby, didn't find supporting libraries. I am considering python as it has a good image processing library and instagram is using it. I want some advise about how the image has to be processed while uploading, efficient way of storage whether database or a file system, image compressions, and precautions to be taken. I would be having profile pictures, do I need store them separately or along with the images? If I want to store the images on a file system, which file system should I use and also should I store the url or should I use any intermediate key value store like redis?

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• Algorithm for Learning development

  - by user9057

  This is a fairly general question. I know a bit of Perl and Python and I am looking to learn programming in more depth so that once I get the hang of it I can start developing applications and then websites. I would like to know of an algorithm (sequence of steps :)) that could describe my approach towards learning programming in general. I have posted small questions on Perl/Python and I have recieved great help from everyone. Note:- I am not in a hurry to learn. I know it takes time and that's fine. Please give any suggestions you think are valid. Also, please don't push me to learn Lisp, Haskell etc - I am a beginner.

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• Resolving equivalence relations

  - by Luca Cerone

  I am writing a function to label the connected component in an image (I know there are several libraries outside, I just wanted to play with the algorithm). To do this I label the connected regions with different labels and create an equivalence table that contain information on the labels belonging to the same connected component. As an example if my equivalence table (vector of vector) looks something like: 1: 1,3 2: 2,3 3: 1,2,3 4: 4 It means that in the image there are 2 different regions, one made of elements that are labelled 1,2,3 and an other made of elements labelled 4. What is an easy and efficient way to resolve the equivalences and end up with something that looks like: 1: 1,2,3 2: 4 that I can use to "merge" the different connected regions belonging to the same connected component? Thanks a lot for the help!

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