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• Are there any well-known algorithms or computer models that computer scientists use to predict FIFA

  - by Khnle

  Occasionally I read news articles that mention about some computer models that computer scientists use to predict winners of some sporting events or the odds for betting which I think there must be a mathematical model behind it. I never bothered to think twice even though I am a "pseudo computer scientist" myself. With the 2010 FIFA World Cup just underway, and since I am also a "pseudo football/soccer player" myself, I just started to wonder about these calculations algorithms. For example, I know one factor is determining the strength of opponents, so that a win against a strong opponent can count more than a win against a weak opponent. But it now kind of gets in a circular loop, or at least how does one determine the strength of a team in the first place, before that team can be considered strong or weak? If it's based on a historical data then there's no way that could be accurate, because those players of the past are no longer on the fields so their impact is none (except maybe if they become coaches like Maradona) Anyway, long question short, if you're happen to be working in this field or have some knowledge, please shed some lights.

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• Lists Hash function

  - by John Retallack

  I'm trying to make a hash function so I can tell if too lists with same sizes contain the same elements. For exemple this is what I want: f((1 2 3))=f((1 3 2))=f((2 1 3))=f((2 3 1))=f((3 1 2))=f((3 2 1)). Any ideea how can I approch this problem ? I've tried doing the sum of squares of all elements but it turned out that there are collisions,for exemple f((2 2 5))=33=f((1 4 4)) which is wrong as the lists are not the same. I'm looking for a simple approach it there are any.

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• Ruby: Efficiently check if a hash's keys include all elements of an Array.

  - by Jason

  I want to compare the keys in a hash of parameters against an array of elements for a match. For example: params = {"key1", "key2", "key3"} params_to_match = ["key2","key3"] I could do this, but I'm sure there is a much more elegant way to acheive the same result params.each_key{|key| if params_to_match.include?(key.to_s) return end }

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• Is there a Perl implementation of Factor Graphs sum-product scheduling?

  - by Timmy

  Are there good example codes of implementations of factor graph sum-product scheduling? I am new to the concept, and would like to see how it gets implemented.

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• Generate sample XML from composite hierarchical structure

  - by Jevgenij Nekrasov

  Let's say I have composite hierarchical structure. Each object in the structure has child collection of the same objects. Each object has XPath property, which stores the exact xpath to the element inside XML file. Right now I am trying to create an extension, which can generate XML string from that hierarchical structure, but first I want to make some sort of research what is the most efficient way to do that? ant what is the easiest way?

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• Minimum number of swaps needed to change Array 1 to Array 2?

  - by Adam

  For example, input is Array 1 = [2, 3, 4, 5] Array 2 = [3, 2, 5, 4] Minimum number of swaps needed are 2. The swaps need not be with adjacent cells, any two elements can be swapped.

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• How to Implement AutoSize

  - by TheCloudlessSky

  I'm trying to figure out a good way to auto-size a Rectangle that has text drawn inside of it. I basically want the size to have a ratio of width/height and then "grow" according to that ratio to fit the text. I've looked at Graphics.MeasureString but I don't think it does what I'm looking for (maybe it does and I'm just using it wrong). I don't want to specify a specific width of the rectangle to be drawn, instead I want to say find the smallest width/height to fit this text but the found rectangle must have some specific ratio of width and height. This doesn't have to be specific to C#, any idea for solving this problem I'm sure can be mapped to C#. Thanks!

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• There is 1TB data on disk with around 1KB per data record. How to find duplicates using 512MB RAM an

  - by user288609

  There is 1TB data on a disk with around 1KB per data record. How to find duplicates using 512MB RAM and infinite disk space?

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• finding long repeated substrings in a massive string

  - by Will

  I naively imagined that I could build a suffix trie where I keep a visit-count for each node, and then the deepest nodes with counts greater than one are the result set I'm looking for. I have a really really long string (hundreds of megabytes). I have about 1 GB of RAM. This is why building a suffix trie with counting data is too inefficient space-wise to work for me. To quote Wikipedia's Suffix tree: storing a string's suffix tree typically requires significantly more space than storing the string itself. The large amount of information in each edge and node makes the suffix tree very expensive, consuming about ten to twenty times the memory size of the source text in good implementations. The suffix array reduces this requirement to a factor of four, and researchers have continued to find smaller indexing structures. And that was wikipedia's comments on the tree, not trie. How can I find long repeated sequences in such a large amount of data, and in a reasonable amount of time (e.g. less than an hour on a modern desktop machine)? (Some wikipedia links to avoid people posting them as the 'answer': Algorithms on strings and especially Longest repeated substring problem ;-) )

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• How to find patterns (lines, circles,...) from a list of points?

  - by Burkhard

  I have a list of points. Each point being an x and y coordinate (both of which are integers). Now I'm trying to find known patterns, such as lines, arcs or circles, knowing that the points are not perfectly on the pattern. What's the best way to do it? I don't have many clues to get started. Edit: the points are ordered. The user is drawing something and the program should detect the best patterns. For instance, if a triangle is drawn, it should detect three lines.

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• Stuck on solving the Minimal Spanning Tree problem.

  - by kunjaan

  I have reduced my problem to finding the minimal spanning tree in the graph. But I want to have one more constraint which is that the total degree for each vertex shouldnt exceed a certain constant factor. How do I model my problem? Is MST the wrong path? Do you know any algorithms that will help me? One more problem: My graph has duplicate edge weights so is there a way to count the number of unique MSTs? Are there algorithms that do this? Thank You. Edit: By degree, I mean the total number of edges connecting the vertex. By duplicate edge weight I mean that two edges have the same weight.

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• How to find kth minimal element in the union of two sorted arrays?

  - by Michael

  This is a homework question. They say it takes O(logN + logM) where N and M are the arrays lengths. Let's name the arrays a and b. Obviously we can ignore all a[i] and b[i] where i k. First let's compare a[k/2] and b[k/2]. Let b[k/2] a[k/2]. Therefore we can discard also all b[i], where i k/2. Now we have all a[i], where i < k and all b[i], where i < k/2 to find the answer. What is the next step?

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• What is the best book for learning about Algorithms?

  - by sheats

  I know what algorithms are, but I have never consciously used or created one for any of the programming that I have done. So I'd like to get a book about the subject - I'd prefer if it was in python but that's not a strict requirement. What book about algorithms helped you most to understand, use, and create algorithms? One book per answer so they can be voted on...

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• What are the core mathematical concepts a good developer should know?

  - by Jose B.

  Since Graduating from a very small school in 2006 with a badly shaped & outdated program (I'm a foreigner & didn't know any better school at the time) I've come to realize that I missed a lot of basic concepts from a mathematical & software perspective that are mostly the foundations of other higher concepts. I.e. I tried to listen/watch the open courseware from MIT on Introduction to Algorithms but quickly realized I was missing several mathematical concepts to better understand the course. So what are the core mathematical concepts a good software engineer should know? And what are the possible books/sites you will recommend me?

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• Optimality of Binary Search

  - by templatetypedef

  Hello all- This may be a silly question, but does anyone know of a proof that binary search is asymptotically optimal? That is, if we are given a sorted list of elements where the only permitted operation on those objects is a comparison, how do you prove that the search can't be done in o(lg n)? (That's little-o of lg n, by the way.) Note that I'm restricting this to elements where the only operation permitted operation is a comparison, since there are well-known algorithms that can beat O(lg n) on expectation if you're allowed to do more complex operations on the data (see, for example, interpolation search). Thanks so much! This has really been bugging me since it seems like it should be simple but has managed to resist all my best efforts. :-)

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• Using MySQL as a job queue

  - by user237815

  I'd like to use MySQL as a job queue. Multiple machines will be producing and consuming jobs. Jobs need to be scheduled; some may run every hour, some every day, etc. It seems fairly straightforward: for each job, have a "nextFireTime" column, and have worker machines search for the job with the nextFireTime, change the status of the record to "inProcess", and then update the nextFireTime when the job ends. The problem comes in when a worker dies silently. It won't be able to update the nextFireTime or set the status back to "idle". Unfortunately, jobs can be long-running, so a reaper thread that looks for jobs that have been inProcess too long isn't an option. There's no timeout value that would work. Can anyone suggest a design pattern that would properly handle unreliable worker machines?

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• How do I find the next multiple of 10 of any integer?

  - by Tommy

  Dynamic integer will be any number from 0 to 150. i.e. - number returns 41, need to return 50. If number is 10 need to return 10. Number is 1 need to return 10. Was thinking I could use the ceiling function if I modify the integer as a decimal...? then use ceiling function, and put back to decimal? Only thing is would also have to know if the number is 1, 2 or 3 digits (i.e. - 7 vs 94 vs 136) Is there a better way to achieve this? Thank You,

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• Interview question : What is the fastest way to generate prime number recursively ?

  - by hilal

  Generation of prime number is simple but what is the fastest way to find it and generate( prime numbers) it recursively ? Here is my solution. However, it is not the best way. I think it is O(N*sqrt(N)). Please correct me, if I am wrong. public static boolean isPrime(int n) { if (n < 2) { return false; } else if (n % 2 == 0 & n != 2) { return false; } else { return isPrime(n, (int) Math.sqrt(n)); } } private static boolean isPrime(int n, int i) { if (i < 2) { return true; } else if (n % i == 0) { return false; } else { return isPrime(n, --i); } } public static void generatePrimes(int n){ if(n < 2) { return ; } else if(isPrime(n)) { System.out.println(n); } generatePrimes(--n); } public static void main(String[] args) { generatePrimes(200); }

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• Fast ceiling of an integer division in C / C++

  - by andand

  Given integer values x and y, C and C++ returns as the quotient q = x/y the floor of the floating point valued equivalent. I'm interestd in a method of returning the ceiling instead? For example, ceil(10/5) = 2 and ceil(11/5) = 3. The obvious approach involves something like: q = x / y; if (q * y < x) ++q; This requires an extra comparison and multiplication; and other methods I've seen (used in fact) involve casting as a float or double. Is there a more direct method that avoids the additional multiplication (or a second division) and branch, and that also avoids casting as a floating point number?

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• Adapting pseudocode to java implementation for finding the longest word in a trie

  - by user1766888

  Referring to this question I asked: How to find the longest word in a trie? I'm having trouble implementing the pseudocode given in the answer. findLongest(trie): //first do a BFS and find the "last node" queue <- [] queue.add(trie.root) last <- nil map <- empty map while (not queue.empty()): curr <- queue.pop() for each son of curr: queue.add(son) map.put(son,curr) //marking curr as the parent of son last <- curr //in here, last indicate the leaf of the longest word //Now, go up the trie and find the actual path/string curr <- last str = "" while (curr != nil): str = curr + str //we go from end to start curr = map.get(curr) return str This is what I have for my method public static String longestWord (DTN d) { Queue<DTN> holding = new ArrayQueue<DTN>(); holding.add(d); DTN last = null; Map<DTN,DTN> test = new ArrayMap<DTN,DTN>(); DTN curr; while (!holding.isEmpty()) { curr = holding.remove(); for (Map.Entry<String, DTN> e : curr.children.entries()) { holding.add(curr.children.get(e)); test.put(curr.children.get(e), curr); } last = curr; } curr = last; String str = ""; while (curr != null) { str = curr + str; curr = test.get(curr); } return str; } I'm getting a NullPointerException at: for (Map.Entry<String, DTN> e : curr.children.entries()) How can I find and fix the cause of the NullPointerException of the method so that it returns the longest word in a trie?

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• How to reduce duplicate web pages when rolling my own search engine?

  - by user198729

  One articles can be posted on many sites the same article on a specific website can be visited by several different urls. How do I reduce duplicated stuff in the above occasions?

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• 3-clique counting in a graph

  - by Legend

  I am operating on a (not so) large graph having about 380K edges. I wrote a program to count the number of 3-cliques in the graph. A quick example: List of edges: A - B B - C C - A C - D List of cliques: A - B - C A 3-clique is nothing but a triangle in a graph. Currently, I am doing this using PHP+MySQL. As expected, it is not fast enough. Is there a way to do this in pure MySQL? (perhaps a way to insert all 3-cliques into a table?)

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• What's a good way to add a large number of small floats together?

  - by splicer

  Say you have 100000000 32-bit floating point values in an array, and each of these floats has a value between 0.0 and 1.0. If you tried to sum them all up like this result = 0.0; for (i = 0; i < 100000000; i++) { result += array[i]; } you'd run into problems as result gets much larger than 1.0. So what are some of the ways to more accurately perform the summation?

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• Automatic images translation to 3d model

  - by farrakhov-bulat

  I'm quite interested in automatic images translation to 3d models. Not really for commercial product, but from the point of possible academic research and implementation. What I'd like to achieve is almost transparent for user process of transformation series of images (fewer is better) to 3d model which might be shown in flash/silverlight/javafx or similar. Consider online furniture store with 3d models of all items in stock. Kinda cool to have ability to see the product in 3d before purchasing it. I managed to find a few pieces of software, like insight3d, but it couldn't be used in my case I guess. So, are there any similar projects or tips for me? If it would require to write that piece of software - I'd really love to dig into research on this field.

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• Finding number of different paths

  - by peiska

  I have a game that one player X wants to pass a ball to player Y, but he can be playing with more than one player and the others players can pass the ball to Y. I want to know how many different paths can the ball take from X to Y? for example if he is playing with 3 players there are 5 different paths, 4 players 16 paths, if he is playing with 20 players there are 330665665962404000 paths, and 40 players 55447192200369381342665835466328897344361743780 that the ball can take. the number max. of players that he can play with is 500. I was thinking in using Catalan Numbers? do you think is a correct approach to solve this? Can you give me some tips.

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