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• Proxy service likes Apache Http

  - by Aptos

  Currently I try to simulate my app as distributed servers, so I let them run on localhost:9000 and localhost:9001, i tried using apache load balancer but it is really hard to config on mac, my idea is the second server localhost:9001 will be kept ideal and the requests only be redirected to them when the first server is downed. Is there any good free program can do that ? (except Apache httpd). Extra functions: my application is written in java and maintain an in-memory object, is there any service that can synchronize that object between 2 servers so they can keep uptodate status of other (the second one takes state of the first one)? Is there any app can support that? Thank you very much.

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• How frequent are network partitions on cloud services?

  - by roja

  Much is made of the CAP trade-off for data storage where conflicts can be introduced if there is a network partition. My question is there any evidence that this is a problem that arises with any significant frequency in modern cloud IAAS services e.g.; EC2, Azure, Rackspace. Is it a problem which, despite being a theoretical roadblock in constructing idealised distributed systems is, in fact, a non-issue for all practical concerns? Has anyone experienced a network partition within one of these systems (within a single data-centre?) If so would you be willing to share any details?

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• PROJECT HELP NEEDED. SOME BASIC CONCEPTS GREAT CONFUSION BECAUSE OF LACK OF PROPER MATERIAL PLEASE H

  - by user287745

  Task ATTENDENCE RECORDER AND MANAGEMENT SYSTEM IN DISTRIBUTED ENVIRONMENT ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Example implementation needed. a main server in each lab where the operator punches in the attendence of the student. =========================================================== scenerio:- a college, 10 departments, all departments have a computer lab with 60-100 computers, the computers within each lab are interconnected and all computers in any department have to dail to a particular number (THE NUMBER GIVEN BY THE COLLEGE INTERNET DEPARTMENT) to get connected to the internet. therefore safe to assume that there is a central location to which all the computers in the college are connected to. there is a 'students attendence portal' which can be accessed using internet explorer, students enter there id and get the particular attendence record regarding to the labs only. a description of the working is like:- 1) the user will select which department, which year has arrived to the lab 2) the selection will give the user a return of all the students name and there roll numbers belonging to that department; 'with a check box to "TICK MARK IF THE STUDENT IS PRESENT" ' 3) A SUBMIT BUTTON when pressed reads the 'id' of the checkbox to determine the "particular count number of the student" from that an id of the student is constructed and that id is inserted with a present. (there is also date and time and much more to normalize the db and to avoid conflicts and keep historic records etc but that you will have to assume) steps taken till this date:- ( please note we are not computer students, we are to select something of some other line as a project!, as you will read in my many post 'i" have designed small websites just out of liking. have never ever done any thing official to implement like this.) * have made the database fully normalized. * have made the website which does the functions required on the database. Testing :- deployed the db and site on a free aspspider server and it worked. tested from several computers. Now the problem please help thank youuuuuuuu a practical demonstration has to be done within the college network. no internet! we have been assigned a lab - 60 computers- to demonstrate. (please dont give replies as 60 computers only! is not a big deal one CPU can manage it. i know that; IT IS A HYPOTHETICAL SITUATION WHERE WE ASSUME THAT 60 IS NOT 60 BUT ITS LIKE 60,000 COMPUTERS) 1a) make a web server, yes iis and put files in www folder and configure server to run aspx files- although a link to a step by step guide will be appreciated)\ ? which version of windows should i ask for xp or win server 2000 something? 2a) make a database server. ( well yes install sql server 2005, okay but then what? just put the database file on a pc share it and append the connection string to the share? ) 3a) make the site accessible from the remaining computers ? http://localhost/sitename ? all users "being operators of the particular lab" have the right to edit, write or delete(in dispute), thereby any "users" who hate our program can make the database inconsistent by accessing te same record and doing different edits and then complaining? so how to prevent this? you know something like when the db table is being written to others can only read but not write.. one big confusion:- IN DISTRIBUTED ENVIRONMENT "how to implement this" where does "distributed environment" come in! meaning :- alright the labs are in different departments but the "database server will be one" the "web server will be one" so whats distributed!?

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• Edges on polygon outlines not always correct

  - by user146780

  I'm using the algorithm below to generate quads which are then rendered to make an outline like this http://img810.imageshack.us/img810/8530/uhohz.png The problem as seen on the image, is that sometimes the lines are too thin when they should always be the same width. My algorithm finds the 4 verticies for the first one then the top 2 verticies of the next ones are the bottom 2 of the previous. This creates connected lines, but it seems to not always work. How could I fix this? This is my algorithm: void OGLENGINEFUNCTIONS::GenerateLinePoly(const std::vector<std::vector<GLdouble>> &input, std::vector<GLfloat> &output, int width) { output.clear(); if(input.size() < 2) { return; } int temp; float dirlen; float perplen; POINTFLOAT start; POINTFLOAT end; POINTFLOAT dir; POINTFLOAT ndir; POINTFLOAT perp; POINTFLOAT nperp; POINTFLOAT perpoffset; POINTFLOAT diroffset; POINTFLOAT p0, p1, p2, p3; for(unsigned int i = 0; i < input.size() - 1; ++i) { start.x = static_cast<float>(input[i][0]); start.y = static_cast<float>(input[i][1]); end.x = static_cast<float>(input[i + 1][0]); end.y = static_cast<float>(input[i + 1][1]); dir.x = end.x - start.x; dir.y = end.y - start.y; dirlen = sqrt((dir.x * dir.x) + (dir.y * dir.y)); ndir.x = static_cast<float>(dir.x * 1.0 / dirlen); ndir.y = static_cast<float>(dir.y * 1.0 / dirlen); perp.x = dir.y; perp.y = -dir.x; perplen = sqrt((perp.x * perp.x) + (perp.y * perp.y)); nperp.x = static_cast<float>(perp.x * 1.0 / perplen); nperp.y = static_cast<float>(perp.y * 1.0 / perplen); perpoffset.x = static_cast<float>(nperp.x * width * 0.5); perpoffset.y = static_cast<float>(nperp.y * width * 0.5); diroffset.x = static_cast<float>(ndir.x * 0 * 0.5); diroffset.y = static_cast<float>(ndir.y * 0 * 0.5); // p0 = start + perpoffset - diroffset //p1 = start - perpoffset - diroffset //p2 = end + perpoffset + diroffset // p3 = end - perpoffset + diroffset p0.x = start.x + perpoffset.x - diroffset.x; p0.y = start.y + perpoffset.y - diroffset.y; p1.x = start.x - perpoffset.x - diroffset.x; p1.y = start.y - perpoffset.y - diroffset.y; if(i > 0) { temp = (8 * (i - 1)); p2.x = output[temp + 2]; p2.y = output[temp + 3]; p3.x = output[temp + 4]; p3.y = output[temp + 5]; } else { p2.x = end.x + perpoffset.x + diroffset.x; p2.y = end.y + perpoffset.y + diroffset.y; p3.x = end.x - perpoffset.x + diroffset.x; p3.y = end.y - perpoffset.y + diroffset.y; } output.push_back(p2.x); output.push_back(p2.y); output.push_back(p0.x); output.push_back(p0.y); output.push_back(p1.x); output.push_back(p1.y); output.push_back(p3.x); output.push_back(p3.y); } } Thanks

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• How can I improve my isometric tile-picking algorithm?

  - by Cypher

  I've spent the last few days researching isometric tile-picking algorithms (converting screen-coordinates to tile-coordinates), and have obviously found a lot of the math beyond my grasp. I have come fairly close and what I have is workable, but I would like to improve on this algorithm as it's a little off and seems to pick down and to the right of the mouse pointer. I've uploaded a video to help visualize the current implementation: http://youtu.be/EqwWcq1zuaM My isometric rendering algorithm is based on what is found at this stackoverflow question's answer, with the exception that my x and y axis' are inverted (x increased down-right, while y increased up-right). Here is where I am converting from screen to tiles: // these next few lines convert the mouse pointer position from screen // coordinates to tile-grid coordinates. cameraOffset captures the current // mouse location and takes into consideration the camera's position on screen. System.Drawing.Point cameraOffset = new System.Drawing.Point( 0, 0 ); cameraOffset.X = mouseLocation.X + (int)camera.Left; cameraOffset.Y = ( mouseLocation.Y + (int)camera.Top ); // the camera-aware mouse coordinates are then further converted in an attempt // to select only the "tile" portion of the grid tiles, instead of the entire // rectangle. this algorithm gets close, but could use improvement. mouseTileLocation.X = ( cameraOffset.X + 2 * cameraOffset.Y ) / Global.TileWidth; mouseTileLocation.Y = -( ( 2 * cameraOffset.Y - cameraOffset.X ) / Global.TileWidth ); Things to make note of: mouseLocation is a System.Drawing.Point that represents the screen coordinates of the mouse pointer. cameraOffset is the screen position of the mouse pointer that includes the position of the game camera. mouseTileLocation is a System.Drawing.Point that is supposed to represent the tile coordinates of the mouse pointer. If you check out the above link to youtube, you'll notice that the picking algorithm is off a bit. How can I improve on this?

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• Determining the maximum stack depth

  - by Joa Ebert

  Imagine I have a stack-based toy language that comes with the operations Push, Pop, Jump and If. I have a program and its input is the toy language. For instance I get the sequence Push 1 Push 1 Pop Pop In that case the maximum stack would be 2. A more complicated example would use branches. Push 1 Push true If .success Pop Jump .continue .success: Push 1 Push 1 Pop Pop Pop .continue: In this case the maximum stack would be 3. However it is not possible to get the maximum stack by walking top to bottom as shown in this case since it would result in a stack-underflow error actually. CFGs to the rescue you can build a graph and walk every possible path of the basic blocks you have. However since the number of paths can grow quickly for n vertices you get (n-1)! possible paths. My current approach is to simplify the graph as much as possible and to have less possible paths. This works but I would consider it ugly. Is there a better (read: faster) way to attack this problem? I am fine if the algorithm produces a stack depth that is not optimal. If the correct stack size is m then my only constraint is that the result n is n = m. Is there maybe a greedy algorithm available that would produce a good result here?

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• Sorting tasks to assign

  - by Diego

  I've got a problem that I don't know where to start. I'd realy appreciate some help. The problem: I have several T task that must be done in D days by just 1 employee (let's forget using several resources right now). Each task can be done in some times (not all tasks can be done all time). e.g.: If my employee starts working at 8 o'clock and one task is "call a client". Maybe the client office opens at 9 o'clock. Also each task has a duration (really estimated). It is supposed that the D days are enough to do all task. I've to sort the tasks to the employee. e.g.: at monday 8:00 do task 7, then at 9:30 starts with task 2. In the example task 7 duration would be 1 and a half hour. Thanks for the help! Diego PD: If someone has a way to make this and it is not an algorithm never minds, please answer and I'll manage to think the algorithm. I just don't know how to face the problem. Edit Would Project be usefull? Edit 2 Tasks / Jobs dependency is NOT required

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• Programmatically creating vector arrows in KML

  - by mettadore

  Does anyone have any practical examples of programmatically drawing icons as vectors in KML? Specifically, I have data with a magnitude and an azimuth at given coordinates, and I would like to have icons (or another graphical element) generated based on these values. Some thoughts on how I might approach it: Image directory (a brute force way): Make an image director of 360 different image files (probably batch rotate a single image) each pointing in a cooresponding azimuth. I've seen things like "Excel to KML," but am looking for code that I can use within a program, rather than a web utility. Issue: Arrow does not contain magnitude context, so that would have to be a label. I'd rather dynamically lengthen the arrow. Line creation in KML: Perhaps create a formula that creates a line with the origin at the coordinate points, with the length of the line proportional to the magnitute, and angled according to azimuth. There would then be two more lines, perhaps 30 degrees or so extending from the end of the previous line to make the arrow head. Issues: Not a separate image icon, so not sure how it would work in KML. Also not sure how easy it would be to generate this algorithm. Separate image generation: Perhaps create a PHP file that uses imagemagick or something similar to dynamically generate a .png file in a similar method to the above, and then link to the icon using the URI "domain.tld/imagegen.php?magnitude=magvalue&azimuth=azmvalue". Issue: Still have the problem of actually writing the algorithm for image generation. So, the question: has anyone else come up with solutions for programmatic vector (rather than merely arrow) generation?

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• method for specialized pathfinding?

  - by rlbond

  I am working on a roguelike in my (very little) free time. Each level will basically be a few rectangular rooms connected together by paths. I want the paths between rooms to be natural-looking and windy, however. For example, I would not consider the following natural-looking: B X X X XX XX XX AXX I really want something more like this: B X XXXX X X X X AXXXXXXXX These paths must satisfy a few properties: I must be able to specify an area inside which they are bounded, I must be able to parameterize how windy and lengthy they are, The lines should not look like they started at one path and ended at the other. For example, the first example above looks as if it started at A and ended at B, because it basically changed directions repeatedly until it lined up with B and then just went straight there. I was hoping to use A*, but honestly I have no idea what my heuristic would be. I have also considered using a genetic algorithm, but I don't know how practical that method might end up. My question is, what is a good way to get the results I want? Please do not just specify a method like "A*" or "Dijkstra's algorithm," because I also need help with a good heuristic.

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• Compression algorithm for IEEE-754 data

  - by David Taylor

  Anyone have a recommendation on a good compression algorithm that works well with double precision floating point values? We have found that the binary representation of floating point values results in very poor compression rates with common compression programs (e.g. Zip, RAR, 7-Zip etc). The data we need to compress is a one dimensional array of 8-byte values sorted in monotonically increasing order. The values represent temperatures in Kelvin with a span typically under of 100 degrees. The number of values ranges from a few hundred to at most 64K. Clarifications All values in the array are distinct, though repetition does exist at the byte level due to the way floating point values are represented. A lossless algorithm is desired since this is scientific data. Conversion to a fixed point representation with sufficient precision (~5 decimals) might be acceptable provided there is a significant improvement in storage efficiency. Update Found an interesting article on this subject. Not sure how applicable the approach is to my requirements. http://users.ices.utexas.edu/~burtscher/papers/dcc06.pdf

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• 3x3 Sobel operator and gradient features

  - by pithyless

  Reading a paper, I'm having difficulty understanding the algorithm described: Given a black and white digital image of a handwriting sample, cut out a single character to analyze. Since this can be any size, the algorithm needs to take this into account (if it will be easier, we can assume the size is 2^n x 2^m). Now, the description states given this image we will convert it to a 512-bit feature (a 512-bit hash) as follows: (192 bits) computes the gradient of the image by convolving it with a 3x3 Sobel operator. The direction of the gradient at every edge is quantized to 12 directions. (192 bits) The structural feature generator takes the gradient map and looks in a neighborhood for certain combinations of gradient values. (used to compute 8 distinct features that represent lines and corners in the image) (128 bits) Concavity generator uses an 8-point star operator to find coarse concavities in 4 directions, holes, and lagrge-scale strokes. The image feature maps are normalized with a 4x4 grid. I'm for now struggling with how to take an arbitrary image, split into 16 sections, and using a 3x3 Sobel operator to come up with 12 bits for each section. (But if you have some insight into the other parts, feel free to comment :)

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• Bitwise Interval Arithmetic

  - by KennyTM

  I've recently read an interesting thread on the D newsgroup, which basically asks, Given two signed integers a ∈ [amin, amax], b ∈ [bmin, bmax], what is the tightest interval of a | b? I'm think if interval arithmetics can be applied on general bitwise operators (assuming infinite bits). The bitwise-NOT and shifts are trivial since they just corresponds to -1 − x and 2n x. But bitwise-AND/OR are a lot trickier, due to the mix of bitwise and arithmetic properties. Is there a polynomial-time algorithm to compute the intervals of bitwise-AND/OR? Note: Assume all bitwise operations run in linear time (of number of bits), and test/set a bit is constant time. The brute-force algorithm runs in exponential time. Because ~(a | b) = ~a & ~b and a ^ b = (a | b) & ~(a & b), solving the bitwise-AND and -NOT problem implies bitwise-OR and -XOR are done. Although the content of that thread suggests min{a | b} = max(amin, bmin), it is not the tightest bound. Just consider [2, 3] | [8, 9] = [10, 11].)

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• C++ design question on traversing binary trees

  - by user231536

  I have a binary tree T which I would like to copy to another tree. Suppose I have a visit method that gets evaluated at every node: struct visit { virtual void operator() (node* n)=0; }; and I have a visitor algorithm void visitor(node* t, visit& v) { //do a preorder traversal using stack or recursion if (!t) return; v(t); visitor(t->left, v); visitor(t->right, v); } I have 2 questions: I settled on using the functor based approach because I see that boost graph does this (vertex visitors). Also I tend to repeat the same code to traverse the tree and do different things at each node. Is this a good design to get rid of duplicated code? What other alternative designs are there? How do I use this to create a new binary tree from an existing one? I can keep a stack on the visit functor if I want, but it gets tied to the algorithm in visitor. How would I incorporate postorder traversals here ? Another functor class?

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• Bubble Breaker Game Solver better than greedy?

  - by Gregory

  For a mental exercise I decided to try and solve the bubble breaker game found on many cell phones as well as an example here:Bubble Break Game The random (N,M,C) board consists N rows x M columns with C colors The goal is to get the highest score by picking the sequence of bubble groups that ultimately leads to the highest score A bubble group is 2 or more bubbles of the same color that are adjacent to each other in either x or y direction. Diagonals do not count When a group is picked, the bubbles disappear, any holes are filled with bubbles from above first, ie shift down, then any holes are filled by shifting right A bubble group score = n * (n - 1) where n is the number of bubbles in the bubble group The first algorithm is a simple exhaustive recursive algorithm which explores going through the board row by row and column by column picking bubble groups. Once the bubble group is picked, we create a new board and try to solve that board, recursively descending down Some of the ideas I am using include normalized memoization. Once a board is solved we store the board and the best score in a memoization table. I create a prototype in python which shows a (2,15,5) board takes 8859 boards to solve in about 3 seconds. A (3,15,5) board takes 12,384,726 boards in 50 minutes on a server. The solver rate is ~3k-4k boards/sec and gradually decreases as the memoization search takes longer. Memoization table grows to 5,692,482 boards, and hits 6,713,566 times. What other approaches could yield high scores besides the exhaustive search? I don't seen any obvious way to divide and conquer. But trending towards larger and larger bubbles groups seems to be one approach Thanks to David Locke for posting the paper link which talks above a window solver which uses a constant-depth lookahead heuristic.

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• intelligent path truncation/ellipsis for display

  - by peterchen

  I am looking for an existign path truncation algorithm (similar to what the Win32 static control does with SS_PATHELLIPSIS) for a set of paths that should focus on the distinct elements. For example, if my paths are like this: Unit with X/Test 3V/ Unit with X/Test 4V/ Unit with X/Test 5V/ Unit without X/Test 3V/ Unit without X/Test 6V/ Unit without X/2nd Test 6V/ When not enough display space is available, they should be truncated to something like this: ...with X/...3V/ ...with X/...4V/ ...with X/...5V/ ...without X/...3V/ ...without X/...6V/ ...without X/2nd ...6V/ (Assuming that an ellipsis generally is shorter than three letters). This is just an example of a rather simple, ideal case (e.g. they'd all end up at different lengths now, and I wouldn't know how to create a good suggestion when a path "Thingie/Long Test/" is added to the pool). There is no given structure of the path elements, they are assigned by the user, but often items will have similar segments. It should work for proportional fonts, so the algorithm should take a measure function (and not call it to heavily) or generate a suggestion list. Data-wise, a typical use case would contain 2..4 path segments anf 20 elements per segment. I am looking for previous attempts into that direction, and if that's solvable wiht sensible amount of code or dependencies.

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• reconstructing a tree from its preorder and postorder lists.

  - by NomeN

  Consider the situation where you have two lists of nodes of which all you know is that one is a representation of a preorder traversal of some tree and the other a representation of a postorder traversal of the same tree. I believe it is possible to reconstruct the tree exactly from these two lists, and I think I have an algorithm to do it, but have not proven it. As this will be a part of a masters project I need to be absolutely certain that it is possible and correct (Mathematically proven). However it will not be the focus of the project, so I was wondering if there is a source out there (i.e. paper or book) I could quote for the proof. (Maybe in TAOCP? anybody know the section possibly?) In short, I need a proven algorithm in a quotable resource that reconstructs a tree from its pre and post order traversals. Note: The tree in question will probably not be binary, or balanced, or anything that would make it too easy. Note2: Using only the preorder or the postorder list would be even better, but I do not think it is possible. Note3: A node can have any amount of children. Note4: I only care about the order of siblings. Left or right does not matter when there is only one child.

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• looking for a license key algorithm.

  - by giulio

  There are alot of questions relating to license keys asked on stackoverflow. But they don't answer this question. Can anyone provide a simple license key algorithm that is technology independent and doesn't required a diploma in mathematics to understand ? The license key algorithm is similar to public key encryption. I just need something simple that can be implemented in any platform .Net/Java and uses simple data like characters. Written as Pseudo code is perfect. So if a person presents a string, a complementary string can be generated that is the authorisation code. Below is a common scenario that it would be used for. Customer downloads s/w which generates a unique key upon initial startup/installation. S/w runs during trial period. At end of trial period an authorisation key is required. Customer goes to designated web-site, enters their code and get authorisation code to enable s/w, after paying :) Don't be afraid to describe your answer as though you're talking to a 5 yr old as I am not a mathemtician.

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• Small-o(n^2) implementation of Polynomial Multiplication

  - by AlanTuring

  I'm having a little trouble with this problem that is listed at the back of my book, i'm currently in the middle of test prep but i can't seem to locate anything regarding this in the book. Anyone got an idea? A real polynomial of degree n is a function of the form f(x)=a(n)x^n+?+a1x+a0, where an,…,a1,a0 are real numbers. In computational situations, such a polynomial is represented by a sequence of its coefficients (a0,a1,…,an). Assuming that any two real numbers can be added/multiplied in O(1) time, design an o(n^2)-time algorithm to compute, given two real polynomials f(x) and g(x) both of degree n, the product h(x)=f(x)g(x). Your algorithm should **not** be based on the Fast Fourier Transform (FFT) technique. Please note it needs to be small-o(n^2), which means it complexity must be sub-quadratic. The obvious solution that i have been finding is indeed the FFT, but of course i can't use that. There is another method that i have found called convolution, where if you take polynomial A to be a signal and polynomial B to be a filter. A passed through B yields a shifted signal that has been "smoothed" by A and the resultant is A*B. This is supposed to work in O(n log n) time. Of course i am completely unsure of implementation. If anyone has any ideas of how to achieve a small-o(n^2) implementation please do share, thanks.

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• Intelligent web features, algorithms (people you may follow, similar to you ...)

  - by hilal

  I have 3 main questions about the algorithms in intelligent web (web 2.0) Here the book I'm reading http://www.amazon.com/Algorithms-Intelligent-Web-Haralambos-Marmanis/dp/1933988665 and I want to learn the algorithms in deeper 1. People You may follow (Twitter) How can one determine the nearest result to my requests ? Data mining? which algorithms? 2. How you’re connected feature (Linkedin) Simply algorithm works like that. It draws the path between two nodes let say between Me and the other person is C. Me - A, B - A connections - C . It is not any brute force algorithms or any other like graph algorithms :) 3. Similar to you (Twitter, Facebook) This algorithms is similar to 1. Does it simply work the max(count) friend in common (facebook) or the max(count) follower in Twitter? or any other algorithms they implement? I think the second part is true because running the loop dict{count, person} for person in contacts: dict.add(count(common(person))) return dict(max) is a silly act in every refreshing page. 4. Did you mean (Google) I know that they may implement it with phonetic algorithm http://en.wikipedia.org/wiki/Phonetic_algorithm simply soundex http://en.wikipedia.org/wiki/Soundex and here is the Google VP of Engineering and CIO Douglas Merrill speak http://www.youtube.com/watch?v=syKY8CrHkck#t=22m03s What about first 3 questions? Any ideas are welcome ! Thanks

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• Calculate total batch upload transfer percent with limited information

  - by GONeale

  Hi there, I have a system which uploads to a server file by file and displays a progress bar on file upload progress, then underneath a second progress bar which I want to indicate percentage of batch complete across all files queued to upload. Information and algorithms I can work out are: Bytes Sent / Total Bytes To Send = First progress bar (eg. 512KB of 1024KB (50%)) That works fine. However supposing I have two other files left to upload, but both file sizes are unknown (as this is only known once the file is about to commence upload, at which point it is compressed and file size is determined) how would I go about making my third progress bar? I didn't think this would be possible as I would need "Total Bytes Sent" / "Total Bytes To Send", to replicate the logic of my first progress bar on a larger scale, however I did get a version working: "Current file number we are on" / "total number of files to send" returning the percentage through the batch, however obviously will not incrementally update and it's pretty crude. So on further thinking I thought if I could incorporate the current file % with this algorithm I could perhaps get the correct progress percentage of my batch's current point. I tried this algorithm, but alas to no such avail (sorry to any math heads, it's probably quite apparent why it won't work) ("Current file number we are on" / "total number of files to send") * ("Bytes Sent" / "Total Bytes To Send") For example I thought I was on the right track when testing with this example: 2/3 (2nd of 3rd file) = 66% (this is right so far) but then when I added * 0.20 (for indicating only 20% of 2nd file has uploaded) we went back to 13%. What I need is only a little over 33%! I did try the inverse at 0.80 and a (2/3 * (2/3 * 0.2)) Can this be done without knowing entire bytes in batch to upload? Please help! Thank you!

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• Spaced repetition (SRS) for learning

  - by Fredrik Johansson

  A client has asked me to add a simple spaced repeition algorithm (SRS) for an onlinebased learning site. But before throwing my self into it, I'd like to discuss it with the community. Basically the site asks the user a bunch of questions (by automatically selecting say 10 out of 100 total questions from a database), and the user gives either a correct or incorrect answer. The users result are then stored in a database, for instance: userid questionid correctlyanswered dateanswered 1 123 0 (no) 2010-01-01 10:00 1 124 1 (yes) 2010-01-01 11:00 1 125 1 (yes) 2010-01-01 12:00 Now, to maximize a users ability to learn all answers, I should be able to apply an SRS algorithm so that a user, next time he takes the quiz, receives questions incorrectly answered more often; than questions answered correctly. Also, questions that are previously answered incorrectly, but recently often answered correctly should occur less often. Have anyone implemented something like this before? Any tips or suggestions? Theese are the best links I've found: http://en.wikipedia.org/wiki/Spaced_repetition http://www.mnemosyne-proj.org/principles.php http://www.supermemo.com/english/ol/sm2.htm

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• Code golf: combining multiple sorted lists into a single sorted list

  - by Alabaster Codify

  Implement an algorithm to merge an arbitrary number of sorted lists into one sorted list. The aim is to create the smallest working programme, in whatever language you like. For example: input: ((1, 4, 7), (2, 5, 8), (3, 6, 9)) output: (1, 2, 3, 4, 5, 6, 7, 8, 9) input: ((1, 10), (), (2, 5, 6, 7)) output: (1, 2, 5, 6, 7, 10) Note: solutions which concatenate the input lists then use a language-provided sort function are not in-keeping with the spirit of golf, and will not be accepted: sorted(sum(lists,[])) # cheating: out of bounds! Apart from anything else, your algorithm should be (but doesn't have to be) a lot faster! Clearly state the language, any foibles and the character count. Only include meaningful characters in the count, but feel free to add whitespace to the code for artistic / readability purposes. To keep things tidy, suggest improvement in comments or by editing answers where appropriate, rather than creating a new answer for each "revision". EDIT: if I was submitting this question again, I would expand on the "no language provided sort" rule to be "don't concatenate all the lists then sort the result". Existing entries which do concatenate-then-sort are actually very interesting and compact, so I won't retro-actively introduce a rule they break, but feel free to work to the more restrictive spec in new submissions. Inspired by http://stackoverflow.com/questions/464342/combining-two-sorted-lists-in-python

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• Using generics to make an algorithm work on lists of "something" instead of only String's

  - by Binary255

  Hi, I have a small algorithm which replaces the position of characters in a String: class Program { static void Main(string[] args) { String pairSwitchedStr = pairSwitch("some short sentence"); Console.WriteLine(pairSwitchedStr); Console.ReadKey(); } private static String pairSwitch(String str) { StringBuilder pairSwitchedStringBuilder = new StringBuilder(); for (int position = 0; position + 1 < str.Length; position += 2) { pairSwitchedStringBuilder.Append((char)str[position + 1]); pairSwitchedStringBuilder.Append((char)str[position]); } return pairSwitchedStringBuilder.ToString(); } } I would like to make it as generic as possible, possibly using Generics. What I'd like to have is something which works with: Anything that is built up using a list of instances. Including strings, arrays, linked lists I suspect that the solution must use generics as the algorithm is working on a list of instances of T (there T is ... something). Version of C# isn't of interest, I guess the solution will be nicer if features from C# version 2.0 is used.

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• categorize a set of phrases into a set of similar phrases

  - by Dingo

  I have a few apps that generate textual tracing information (logs) to log files. The tracing information is the typical printf() style - i.e. there are a lot of log entries that are similar (same format argument to printf), but differ where the format string had parameters. What would be an algorithm (url, books, articles, ...) that will allow me to analyze the log entries and categorize them into several bins/containers, where each bin has one associated format? Essentially, what I would like is to transform the raw log entries into (formatA, arg0 ... argN) instances, where formatA is shared among many log entries. The formatA does not have to be the exact format used to generate the entry (even more so if this makes the algo simpler). Most of the literature and web-info I found deals with exact matching, a max substring matching, or a k-difference (with k known/fixed ahead of time). Also, it focuses on matching a pair of (long) strings, or a single bin output (one match among all input). My case is somewhat different, since I have to discover what represents a (good-enough) match (generally a sequence of discontinuous strings), and then categorize each input entries to one of the discovered matches. Lastly, I'm not looking for a perfect algorithm, but something simple/easy to maintain. Thanks!

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• What does O(log n) mean exactly?

  - by Andreas Grech

  I am currently learning about Big O Notation running times and amortized times. I understand the notion of O(n) linear time, meaning that the size of the input affects the growth of the algorithm proportionally...and the same goes for, for example, quadratic time O(n2) etc..even algorithms, such as permutation generators, with O(n!) times, that grow by factorials. For example, the following function is O(n) because the algorithm grows in proportion to its input n: f(int n) { int i; for (i = 0; i < n; ++i) printf("%d", i); } Similarly, if there was a nested loop, the time would be O(n2). But what exactly is O(log n)? For example, what does it mean to say that the height of a complete binary tree is O(log n)? I do know (maybe not in great detail) what Logarithm is, in the sense that: log10 100 = 2, but I cannot understand how to identify a function with a logarithmic time.

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