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• Priority queue with dynamic item priorities.

  - by sean

  I need to implement a priority queue where the priority of an item in the queue can change and the queue adjusts itself so that items are always removed in the correct order. I have some ideas of how I could implement this but I'm sure this is quite a common data structure so I'm hoping I can use an implementation by someone smarter than me as a base. Can anyone tell me the name of this type of priority queue so I know what to search for or, even better, point me to an implementation?

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• Make function non-recursive

  - by user69514

  I'm not sure how to make this function non-recursive. Any ideas?: void foo(int a, int b){ while( a < len && arr[a][b] != -1){ if(++a == len){ a = 0; b++; } } if( a == len){ size++; return; } if( a < (len-1)){ arr[a][b] = 1; arr[a][(b+1)] = 1; foo(a, b); arr[a][b] = -1; arr[a][(b+1)] = -1; } if( a < (len-1) && arr[(a+1)][b] == -1){ arr[a][b] = 0; arr[(a+1)][b] = 0; foo(a,b); arr[a][b] = -1; arr[(a+1)][b] = -1; } }

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• Auto scale and rotate images

  - by Dave Jarvis

  Given: two images of the same subject matter; the images have the same resolution, colour depth, and file format; the images differ in size and rotation; and two lists of (x, y) co-ordinates that correlate the images. I would like to know: How do you transform the larger image so that it visually aligns to the second image? (Optional.) What are the minimum number of points needed to get an accurate transformation? (Optional.) How far apart do the points need to be to get an accurate transformation? The transformation would need to rotate, scale, and possibly shear the larger image. Essentially, I want to create (or find) a program that does the following: Input two images (e.g., TIFFs). Click several anchor points on the small image. Click the several corresponding anchor points on the large image. Transform the large image such that it maps to the small image by aligning the anchor points. This would help align pictures of the same stellar object. (For example, a hand-drawn picture from 1855 mapped to a photograph taken by Hubble in 2000.) Many thanks in advance for any algorithms (preferably Java or similar pseudo-code), ideas or links to related open-source software packages.

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• OpenGL ES Highlighting Algorithm for the iPhone

  - by user280556

  Hey Everyone, I am trying to do a highlighting action on the iPhone. I can draw lines an such with the finger but now I want to be able to highlight over that. Any algorithms out there you can point me to that does that? Using OpenGL ES off course. Thanks

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• Data Structures for hashMap, List and Set

  - by harigm

  Can any one please guide me to look in depth about the Data Structures used and how is it implemented in the List, Set and Maps of Util Collection page. In Interviews most of the questions will be on the Algorithms, but I never saw anywhere the implementation details, Can any one please share the information.

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• How much time should it take to find the sum of all prime numbers less than 2 million?

  - by Shahensha

  I was trying to solve this Project Euler Question. I implemented the sieve of euler as a helper class in java. It works pretty well for the small numbers. But when I input 2 million as the limit it doesn't return the answer. I use Netbeans IDE. I waited for a lot many hours once, but it still didn't print the answer. When I stopped running the code, it gave the following result Java Result: 2147483647 BUILD SUCCESSFUL (total time: 2,097 minutes 43 seconds) This answer is incorrect. Even after waiting for so much time, this isn't correct. While the same code returns correct answers for smaller limits. Sieve of euler has a very simple algo given at the botton of this page. My implementation is this: package support; import java.util.ArrayList; import java.util.List; /** * * @author admin */ public class SieveOfEuler { int upperLimit; List<Integer> primeNumbers; public SieveOfEuler(int upperLimit){ this.upperLimit = upperLimit; primeNumbers = new ArrayList<Integer>(); for(int i = 2 ; i <= upperLimit ; i++) primeNumbers.add(i); generatePrimes(); } private void generatePrimes(){ int currentPrimeIndex = 0; int currentPrime = 2; while(currentPrime <= Math.sqrt(upperLimit)){ ArrayList<Integer> toBeRemoved = new ArrayList<Integer>(); for(int i = currentPrimeIndex ; i < primeNumbers.size() ; i++){ int multiplier = primeNumbers.get(i); toBeRemoved.add(currentPrime * multiplier); } for(Integer i : toBeRemoved){ primeNumbers.remove(i); } currentPrimeIndex++; currentPrime = primeNumbers.get(currentPrimeIndex); } } public List getPrimes(){ return primeNumbers; } public void displayPrimes(){ for(double i : primeNumbers) System.out.println(i); } } I am perplexed! My questions is 1) Why is it taking so much time? Is there something wrong in what I am doing? Please suggest ways for improving my coding style, if you find something wrong.

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• Sort months ( with strings ) algorithm

  - by Oscar Reyes

  I have this months array: ["January", "March", "December" , "October" ] And I want to have it sorted like this: ["January", "March", "October", "December" ] I'm currently thinking in a "if/else" horrible cascade but I wonder if there is some other way to do this. The bad part is that I need to do this only with "string" ( that is, without using Date object or anything like that ) What would be a good approach?

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• C - How to implement Set data structure?

  - by psihodelia

  Is there any tricky way to implement a set data structure (a collection of unique values) in C? All elements in a set will be of the same type and there is a huge RAM memory. As I know, for integers it can be done really fast'N'easy using value-indexed arrays. But I'd like to have a very general Set data type. And it would be nice if a set could include itself.

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• Load balancing and scheduling algorithms.

  - by Lukas Šalkauskas

  Hello there, so here is my problem: I have several different configuarion servers. I have different calculations (jobs); I can predict how long approximately each job will take to be caclulated. Also, I have priorities. My question is how to keep all machines loaded 99-100% and schedule the jobs in the best way. Each machine can do several calculations at a time. Jobs are pushed to the machine. The central machine knows the current load of each machine. Also, I would like to to assign some kind of machine learning here, because I will know statistics of each job (started, finished, cpu load etc.). How can I distribute jobs (calculations) in the best possible way, keeping in mind the priorities? Any suggestions, ideas, or algorithms ? FYI: My platform .NET.

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• assignment vs std::swap and merging and keeping duplicates in seperate object

  - by rubenvb

  Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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• Quick way to do data lookup in PHP

  - by Ghostrider

  I have a data table with 600,000 records that is around 25 megabytes large. It is indexed by a 4 byte key. Is there a way to find a row in such dataset quickly with PHP without resorting to MySQL? The website in question is mostly static with minor PHP code and no database dependencies and therefore fast. I would like to add this data without having to use MySQL if possible. In C++ I would memory map the file and do a binary search in it. Is there a way to do something similar in PHP?

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• Is there "good" PRNG generating values without hidden state?

  - by actual

  I need some good pseudo random number generator that can be computed like a pure function from its previous output without any state hiding. Under "good" I mean: I must be able to parametrize generator in such way that running it for 2^n iterations with any parameters should cover all or almost all values between 0 and 2^n - 1, where n is the number of bits in output value. Combined generator output of n + p bits must cover all or almost all values between 0 and 2^(n + p) - 1 if I run it for 2^n iterations for every possible combination of its parameters, where p is the number of bits in parameters. For example, LCG can be computed like a pure function and it can meet first condition, but it can not meet second one. Say, we have 32-bit generator, m = 2^32 and it is constant, our p = 64 (two 32-bit parameters a and c), n + p = 96, so we must peek data by three ints from output to meet second condition. Unfortunately, condition can not be meet because of strictly alternating sequence of odd and even ints in output. To overcome this, hidden state must be introduced, but that makes function not pure and breaks first condition (period become much longer). Am I wanting too much?

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• How does the Amazon Recommendation feature work?

  - by Rachel

  What technology goes in behind the screens of Amazon recommendation technology? I believe that Amazon recommendation is currently the best in the market, but how do they provide us with such relevant recommendations? Recently, we have been involved with similar recommendation kind of project, but would surely like to know about the in and outs of the Amazon recommendation technology from a technical standpoint. Any inputs would be highly appreciated. Update: This patent explains how personalized recommendations are done but it is not very technical, and so it would be really nice if some insights could be provided. From the comments of Dave, Affinity Analysis forms the basis for such kind of Recommendation Engines. Also here are some good reads on the Topic Demystifying Market Basket Analysis Market Basket Analysis Affinity Analysis Suggested Reading: Data Mining: Concepts and Technique

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• CRC function without order dependancy

  - by Pirks

  I need CRC mechanism allow to calculate CRC of number of strings string A,B crc(A) + crc(B) == crc(A+B) P.S. XOR too weak.

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• What is the optimum way to select the most dissimilar individuals from a population?

  - by Aaron D

  I have tried to use k-means clustering to select the most diverse markers in my population, for example, if we want to select 100 lines I cluster the whole population to 100 clusters then select the closest marker to the centroid from each cluster. The problem with my solution is it takes too much time (probably my function needs optimization), especially when the number of markers exceeds 100000. So, I will appreciate it so much if anyone can show me a new way to select markers that maximize diversity in my population and/or help me optimize my function to make it work faster. Thank you # example: library(BLR) data(wheat) dim(X) mdf<-mostdiff(t(X), 100,1,nstart=1000) Here is the mostdiff function that i used: mostdiff <- function(markers, nClust, nMrkPerClust, nstart=1000) { transposedMarkers <- as.array(markers) mrkClust <- kmeans(transposedMarkers, nClust, nstart=nstart) save(mrkClust, file="markerCluster.Rdata") # within clusters, pick the markers that are closest to the cluster centroid # turn the vector of which markers belong to which clusters into a list nClust long # each element of the list is a vector of the markers in that cluster clustersToList <- function(nClust, clusters) { vecOfCluster <- function(whichClust, clusters) { return(which(whichClust == clusters)) } return(apply(as.array(1:nClust), 1, vecOfCluster, clusters)) } pickCloseToCenter <- function(vecOfCluster, whichClust, transposedMarkers, centers, pickHowMany) { clustSize <- length(vecOfCluster) # if there are fewer than three markers, the center is equally distant from all so don't bother if (clustSize < 3) return(vecOfCluster[1:min(pickHowMany, clustSize)]) # figure out the distance (squared) between each marker in the cluster and the cluster center distToCenter <- function(marker, center){ diff <- center - marker return(sum(diff*diff)) } dists <- apply(transposedMarkers[vecOfCluster,], 1, distToCenter, center=centers[whichClust,]) return(vecOfCluster[order(dists)[1:min(pickHowMany, clustSize)]]) } }

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• Another Nim's Game Variant

  - by Terry Smith

  Given N binary sequence Example : given one sequence 101001 means player 0 can only choose a position with 0 element and cut the sequence from that position {1,101,1010} player 1 can only choose a position with 1 element ans cut the sequence from that position {null,10,101000} now player 0 and player 1 take turn cutting the sequence, on each turn they can cut any one non-null sequence, if a player k can't make a move because there's no more k element on any sequence, he lose. Assume both player play optimally, who will win ? I tried to solve this problem with grundy but i'm unable to reduce the sequence to a grundy number because it both player don't have the same option to move. Can anyone give me a hint to solve this problem ?

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• Google Jam 2009. C. Welcome to Code Jam. Can't understand Dynamic programming

  - by vibneiro

  The original link of the problem is here: https://code.google.com/codejam/contest/90101/dashboard#s=p2&a=2 In simple words we need to find how many times the string S="welcome to code jam" appears as a sub-sequence of given string S, e.g. S="welcome to code jam" T="wweellccoommee to code qps jam" I know the theory but not good at DP in practice. Would you please explain step-by-step process to solve this DP problem on example and why it works?

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• Efficient algorithm to distribute work?

  - by Zwei Steinen

  It's a bit complicated to explain but here we go. We have problems like this (code is pseudo-code, and is only for illustrating the problem. Sorry it's in java. If you don't understand, I'd be glad to explain.). class Problem { final Set<Integer> allSectionIds = { 1,2,4,6,7,8,10 }; final Data data = //Some data } And a subproblem is: class SubProblem { final Set<Integer> targetedSectionIds; final Data data; SubProblem(Set<Integer> targetedSectionsIds, Data data){ this.targetedSectionIds = targetedSectionIds; this.data = data; } } Work will look like this, then. class Work implements Runnable { final Set<Section> subSections; final Data data; final Result result; Work(Set<Section> subSections, Data data) { this.sections = SubSections; this.data = data; } @Override public void run(){ for(Section section : subSections){ result.addUp(compute(data, section)); } } } Now we have instances of 'Worker', that have their own state sections I have. class Worker implements ExecutorService { final Map<Integer,Section> sectionsIHave; { sectionsIHave = {1:section1, 5:section5, 8:section8 }; } final ExecutorService executor = //some executor. @Override public void execute(SubProblem problem){ Set<Section> sectionsNeeded = fetchSections(problem.targetedSectionIds); super.execute(new Work(sectionsNeeded, problem.data); } } phew. So, we have a lot of Problems and Workers are constantly asking for more SubProblems. My task is to break up Problems into SubProblem and give it to them. The difficulty is however, that I have to later collect all the results for the SubProblems and merge (reduce) them into a Result for the whole Problem. This is however, costly, so I want to give the workers "chunks" that are as big as possible (has as many targetedSections as possible). It doesn't have to be perfect (mathematically as efficient as possible or something). I mean, I guess that it is impossible to have a perfect solution, because you can't predict how long each computation will take, etc.. But is there a good heuristic solution for this? Or maybe some resources I can read up before I go into designing? Any advice is highly appreciated!

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• Parsing a comma-separated list

  - by alex

  I have a comma-separated list of values, for example: strins s = "param1=true;param2=4;param3=2.0f;param4=sometext;"; I need a functions: public bool ExtractBool(string parameterName, string @params); public int ExtractInt(string parameterName, string @params); public float ExtractFloat(string parameterName, string @params); public string ExtractString(string parameterName, string @params); Is there a special functions in .net that can help me with csl ? PS: parameter names are equal within a list.

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• Finding cities close to one another using longitude and latitude

  - by Jamie

  Each user in my db is associated to a city (with it's longitude and latitude) How would I go about finding out which cities are close to one another? i.e. in England, Cambridge is fairly close to London. So If I have a user who lives in Cambridge. Users close to them would be users living in close surrounding cities, such as London, Hertford etc. Any ideas how I could go about this? And also, how would I define what is close? i.e. in the UK close would be much closer than if it were in the US as the US is far more spread out. Ideas and suggestions. Also, do you know any services that provide this sort of functionality? Thanks

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• How do I remove the leaves of a binary tree?

  - by flopex

  I'm trying to remove all of the leaves. I know that leaves have no children, this is what I have so far. public void removeLeaves(BinaryTree n){ if (n.left == null && n.right == null){ n = null; } if (n.left != null) removeLeaves(n.left); if (n.right != null) removeLeaves(n.right); }

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• .NET Performance: Deep Recursion vs Queue

  - by JeffN825

  I'm writing a component that needs to walk large object graphs, sometimes 20-30 levels deep. What is the most performant way of walking the graph? A. Enqueueing "steps" so as to avoid deep recursion or B. A DFS (depth first search) which may step many levels deep and have a "deep" stack trace at times. I guess the question I'm asking is: Is there a performance hit in .NET for doing a DFS that causes a "deep" stack trace? If so, what is the hit? And would I better better off with some BFS by means of queueing up steps that would have been handled recursively in a DFS? Sorry if I'm being unclear. Thanks.

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• Find the set of largest contiguous rectangles to cover multiple areas

  - by joelpt

  I'm working on a tool called Quickfort for the game Dwarf Fortress. Quickfort turns spreadsheets in csv/xls format into a series of commands for Dwarf Fortress to carry out in order to plot a "blueprint" within the game. I am currently trying to optimally solve an area-plotting problem for the 2.0 release of this tool. Consider the following "blueprint" which defines plotting commands for a 2-dimensional grid. Each cell in the grid should either be dug out ("d"), channeled ("c"), or left unplotted ("."). Any number of distinct plotting commands might be present in actual usage. . d . d c c d d d d c c . d d d . c d d d d d c . d . d d c To minimize the number of instructions that need to be sent to Dwarf Fortress, I would like to find the set of largest contiguous rectangles that can be formed to completely cover, or "plot", all of the plottable cells. To be valid, all of a given rectangle's cells must contain the same command. This is a faster approach than Quickfort 1.0 took: plotting every cell individually as a 1x1 rectangle. This video shows the performance difference between the two versions. For the above blueprint, the solution looks like this: . 9 . 0 3 2 8 1 1 1 3 2 . 1 1 1 . 2 7 1 1 1 4 2 . 6 . 5 4 2 Each same-numbered rectangle above denotes a contiguous rectangle. The largest rectangles take precedence over smaller rectangles that could also be formed in their areas. The order of the numbering/rectangles is unimportant. My current approach is iterative. In each iteration, I build a list of the largest rectangles that could be formed from each of the grid's plottable cells by extending in all 4 directions from the cell. After sorting the list largest first, I begin with the largest rectangle found, mark its underlying cells as "plotted", and record the rectangle in a list. Before plotting each rectangle, its underlying cells are checked to ensure they are not yet plotted (overlapping a previous plot). We then start again, finding the largest remaining rectangles that can be formed and plotting them until all cells have been plotted as part of some rectangle. I consider this approach slightly more optimized than a dumb brute-force search, but I am wasting a lot of cycles (re)calculating cells' largest rectangles and checking underlying cells' states. Currently, this rectangle-discovery routine takes the lion's share of the total runtime of the tool, especially for large blueprints. I have sacrificed some accuracy for the sake of speed by only considering rectangles from cells which appear to form a rectangle's corner (determined using some neighboring-cell heuristics which aren't always correct). As a result of this 'optimization', my current code doesn't actually generate the above solution correctly, but it's close enough. More broadly, I consider the goal of largest-rectangles-first to be a "good enough" approach for this application. However I observe that if the goal is instead to find the minimum set (fewest number) of rectangles to completely cover multiple areas, the solution would look like this instead: . 3 . 5 6 8 1 3 4 5 6 8 . 3 4 5 . 8 2 3 4 5 7 8 . 3 . 5 7 8 This second goal actually represents a more optimal solution to the problem, as fewer rectangles usually means fewer commands sent to Dwarf Fortress. However, this approach strikes me as closer to NP-Hard, based on my limited math knowledge. Watch the video if you'd like to better understand the overall strategy; I have not addressed other aspects of Quickfort's process, such as finding the shortest cursor-path that plots all rectangles. Possibly there is a solution to this problem that coherently combines these multiple strategies. Help of any form would be appreciated.

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• How can I solve the Log Pile wooden puzzle with a computer program?

  - by craig1410

  Can anyone suggest how to solve the Log Pile wooden puzzle using a computer program? See here to visualise the puzzle: http://www.puzzlethis.co.uk/products/madcow/the_log_pile.htm The picture only shows some of the pieces. The full set of 10 pieces are configured as follows with 1 representing a peg, -1 representing a hole and 0 representing neither a peg nor a hole. -1,1,0,-1,0 1,0,1,0,0 1,-1,1,0,0 -1,-1,0,0,-1 -1,1,0,1,0 0,1,0,0,1 1,0,-1,0,-1 0,-1,0,1,0 0,0,-1,1,-1 1,0,-1,0,0 The pieces can be interlocked in two layers of 5 pieces each with the top layer at 90 degrees to the bottom layer as shown in the above link. I have already created a solution to this problem myself using Java but I feel that it was a clumsy solution and I am interested to see some more sophisticated solutions. Feel free to either suggest a general approach or to provide a working program in the language of your choice. My approach was to use the numeric notation above to create an array of "Logs". I then used a combination/permutation generator to try all possible arrangements of the Logs until a solution was found where all the intersections equated to zero (ie. Peg to Hole, Hole to Peg or Blank to Blank). I used some speed-ups to detect the first failed intersection for a given permutation and move on to the next permutation. I hope you find this as interesting as I have. Thanks, Craig.

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• How does the Ableton warp algorithm work exactly?

  - by pepperdreamteam

  I'm looking for any documentation or definitive information on Ableton's warp feature. I understand that it has something to do with finding transients, aligning them with an even rhythm and shifting audio samples accordingly. I'm hoping to find ways to approximate warping with more basic audio editing tools. I understand that this is ableton's unique device, really any information about how it works would be helpful. So...does anyone have any 411?

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