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  • Low CPU/Memory/Memory-bandwith Pathfinding (maybe like in Warcraft 1)

    - by Valmond
    Dijkstra and A* are all nice and popular but what kind of algorithm was used in Warcraft 1 for pathfinding? I remember that the enemy could get trapped in bowl-like caverns which means there were (most probably) no full-path calculations from "start to end". If I recall correctly, the algorithm could be something like this: A) Move towards enemy until success or hitting a wall B) If blocked by a wall, follow the wall until you can move towards the enemy without being blocked and then do A) But I'd like to know, if someone knows :-) [edit] As explained to Byte56, I'm searching for a low cpu/mem/mem-bandwidth algo and wanted to know if Warcraft had some special secrets to deliver (never seen that kind of pathfinding elsewhere), I hope that that is more concordant with the stackexchange rules.

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  • Algorithm to simplify building/structural meshes

    - by morpheus
    I am looking for an algorithm to simplify the meshes of buildings or similar structures. EDIT: I had made a comment that Hoppe's algorithm tends to make meshes more and more spherical with simplification. But, I am not sure about it, so am deleting the comment. Buildings in contrast should tend to become more and more rectangular with increasing simplification. The D3DX extensions for D3D in version 9.0 (d3dx9.lib) used to have classes to do progressive mesh simplification. See: http://doc.51windows.net/Directx9_SDK/?url=/directx9_sdk/graphics/reference/d3dx/functions/mesh/d3dxgeneratepmesh.htm http://msdn.microsoft.com/en-us/library/windows/desktop/bb281243(v=vs.85).aspx

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  • booth multiplication algorithm

    - by grassPro
    Is booth algorithm for multiplication only for multiplying 2 negative numbers (-3 * -4) or one positive and one negative number (-3 * 4) ? Whenever i multiply 2 positive numbers using booth algorithm i get a wrong result. example : 5 * 4 A = 101 000 0 // binary of 5 is 101 S = 011 000 0 // 2's complement of 5 is 011 P = 000 100 0 // binary of 4 is 100 x = 3 y = 3 m = 5 -m = 2's complement of m r = 4 After right shift of P by 1 bit 0 000 100 After right shift of P by 1 bit 0 000 010 P+S = 011 001 0 After right shift by 1 bit 0 011 001 Discarding the LSB 001100 But that comes out to be the binary of 12 . It should have been 20(010100)

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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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  • A look at an example of anti-spam algorithm

    - by pragmaticCamel
    What is a good approach to an anti-spam algorithm for a website similar to reddit? Their anti-spam algorithm seems awfully broken (banning on words in the title and doing a horrible job for that matter). Considering a post spam because it has the word 'spam' in the title is really not a wise choice. Anyway, how can one approach such problem ? Are there any tools that help in such cases? Also, what are the /technical/ reasons behind reddit's choice not using reCAPTCHA on every post submission? It seems like a much better solution than what they have right now. Since reddit is basically a community-driven website why not give such power to the communities' trusted members?

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  • Application of LGPL license on a simple algorithm

    - by georgesl
    The "scope" of the GNU license is troubling me : I know it has been answered many times ( here, here, ... ) but shouldn't we take into consideration the complexity and originality of a code before using GPL license ? I explain : I'm working on a pet project using the DTW algorithm that I have written in C using the pseudo-code given on the wikipedia page . At one point I decided to change it for a C++ implementation ( just for hone my c++ skill ) . After doing so, I've looked for an existing implementation on the web, to compare the "cleanliness" of it, and I found this one : Vectored DTW implementation, which is part of limproved, a C++ library licensed under GPL v3 . Personnally, I don't mind the GNU license because it is a personnal project, which will never led to any kind of commercial purpose, but I wonder if this implementation can abide a company using it to open their code ( and other FOSS permissions ). Theoretically, I think it can ( I may be wrong :p ), but the algorithm in question is so simple (and old) that it should not.

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  • Any great books of algorithm puzzles to practice whiteboard coding with?

    - by jboxer
    I'm looking to get some practice coding solutions to algorithm puzzles on a whiteboard. A friend is going to read puzzles to me (as if he were interviewing me), and I'll solve them on a whiteboard. Does anyone know any great books with algorithm puzzles that would be useful for this? I found a book called Puzzles for Programmers and Pros, but it only has six reviews on Amazon, so I'm not sure how good it really is. If anyone has any recommendations, I'd really appreciate it. Thanks a bunch.

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  • Making change recursively: How do I modify my algorithm to print all combinations?

    - by cb
    I have an algorithm that recursively makes change in the following manner: public static int makeChange(int amount, int currentCoin) { //if amount = zero, we are at the bottom of a successful recursion if (amount == 0){ //return 1 to add this successful solution return 1; //check to see if we went too far }else if(amount < 0){ //don't count this try if we went too far return 0; //if we have exhausted our list of coin values }else if(currentCoin < 0){ return 0; }else{ int firstWay = makeChange(amount, currentCoin-1); int secondWay = makeChange(amount - availableCoins[currentCoin], currentCoin); return firstWay + secondWay; } } However, I'd like to add the capability to store or print each combination as they successfully return. I'm having a bit of a hard time wrapping my head around how to do this. The original algorithm was pretty easy, but now I am frustrated. Any suggestions? CB

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  • Most efficient algorithm for mesh-level, optimal occlusion culling?

    - by Fredriku73
    I am new to culling. On a first glance, it seems that most occlusion culling algorithms are object-level, not examining single meshes, which would be practical for game rendering. What I am looking for is an algorithm that culls all meshes within a single object that are occluded for a given viewpoint, with high accuracy. It needs to be at least O(n log n), a naive mesh-by-mesh comparison (O(n^2)) is too slow. I notice that the Blender GUI identifies the occluded meshes for you in real-time, even if you work with large objects of 10,000+ meshes. What algorithm is used there, pray tell?

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  • Looking for an algorithm in vb.net or c# but I don't know it's name!

    - by Jules
    I'll do my best to explain what the algorithm is supposed to do: There's a class 'Recipe'. Each Recipe can include other Recipes but cannot include itself or any other Recipe that includes it. So, a simple example is we have just two Recipes A & B. If A adds B first, then later on B cannot add A because it will cause a loop. A more complicated example is: A,B,C (1) Recipe C Adds B (2) Recipe B Adds A (3) Recipe A attempts to add C, but can't because of the relationship. C - B - A. I can do this myself, I just wondered if this was a standard named algorithm and I could grab the optimal solution. Thanks

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  • Is there an existing algorithm for this notation translation/conversion?

    - by John
    A system has a notation that would require writing an expression like (A+B)*C as #MUL(#ADD(A,B),C). Is there already an algorithm to do this kind of notation conversion so users can enter in a more conventional way? In other words an algorithm to convert from infix - my notation. First issue is I don't know an exact name for my notation... it's similar to reverse-polish but not quite. Every operator is encoded as a function taking arguments.

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  • Algorithm: Determine shape of two sectors delineated by an arbitrary path, and then fill one.

    - by Arseniy Banayev
    NOTE: This is a challenging problem for anybody who likes logic problems, etc. Consider a rectangular two-dimensional grid of height H and width W. Every space on the grid has a value, either 0 1 or 2. Initially, every space on the grid is a 0, except for the spaces along each of the four edges, which are initially a 2. Then consider an arbitrary path of adjacent (horizontally or vertically) grid spaces. The path begins on a 2 and ends on a different 2. Every space along the path is a 1. The path divides the grid into two "sectors" of 0 spaces. There is an object that rests on an unspecified 0 space. The "sector" that does NOT contain the object must be filled completely with 2. Define an algorithm that determines the spaces that must become 2 from 0, given an array (list) of values (0, 1, or 2) that correspond to the values in the grid, going from top to bottom and then from left to right. In other words, the element at index 0 in the array contains the value of the top-left space in the grid (initially a 2). The element at index 1 contains the value of the space in the grid that is in the left column, second from the top, and so forth. The element at index H contains the value of the space in the grid that is in the top row but second from the left, and so forth. Once the algorithm finishes and the empty "sector" is filled completely with 2s, the SAME algorithm must be sufficient to do the same process again. The second (and on) time, the path is still drawn from a 2 to a different 2, across spaces of 0, but the "grid" is smaller because the 2s that are surrounded by other 2s cannot be touched by the path (since the path is along spaces of 0). I thank whomever is able to figure this out for me, very very much. This does not have to be in a particular programming language; in fact, pseudo-code or just English is sufficient. Thanks again! If you have any questions, just leave a comment and I'll specify what needs to be specified.

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  • Algorithm Question.. Linked List..

    - by AGeek
    Hi, Scenario is as follows:- I want to reverse the direction of the singly linked list, In other words, after the reversal all pointers should now point backwards.. Well the algorithm should take linear time. The solution that i have thought of using another datastructure A Stack.. With the help of which the singly linked list would be easily reversed, with all pointers pointing backwards.. But i am in doubt, that whether the following implementation yeild linear time complexity.. Please comment on this.. And if any other efficient algorithm is in place, then please discuss.. Thanks.

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  • Scalable / Parallel Large Graph Analysis Library?

    - by Joel Hoff
    I am looking for good recommendations for scalable and/or parallel large graph analysis libraries in various languages. The problems I am working on involve significant computational analysis of graphs/networks with 1-100 million nodes and 10 million to 1+ billion edges. The largest SMP computer I am using has 256 GB memory, but I also have access to an HPC cluster with 1000 cores, 2 TB aggregate memory, and MPI for communication. I am primarily looking for scalable, high-performance graph libraries that could be used in either single or multi-threaded scenarios, but parallel analysis libraries based on MPI or a similar protocol for communication and/or distributed memory are also of interest for high-end problems. Target programming languages include C++, C, Java, and Python. My research to-date has come up with the following possible solutions for these languages: C++ -- The most viable solutions appear to be the Boost Graph Library and Parallel Boost Graph Library. I have looked briefly at MTGL, but it is currently slanted more toward massively multithreaded hardware architectures like the Cray XMT. C - igraph and SNAP (Small-world Network Analysis and Partitioning); latter uses OpenMP for parallelism on SMP systems. Java - I have found no parallel libraries here yet, but JGraphT and perhaps JUNG are leading contenders in the non-parallel space. Python - igraph and NetworkX look like the most solid options, though neither is parallel. There used to be Python bindings for BGL, but these are now unsupported; last release in 2005 looks stale now. Other topics here on SO that I've looked at have discussed graph libraries in C++, Java, Python, and other languages. However, none of these topics focused significantly on scalability. Does anyone have recommendations they can offer based on experience with any of the above or other library packages when applied to large graph analysis problems? Performance, scalability, and code stability/maturity are my primary concerns. Most of the specialized algorithms will be developed by my team with the exception of any graph-oriented parallel communication or distributed memory frameworks (where the graph state is distributed across a cluster).

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  • An old flaw in X Window System. How does it work?

    - by Legend
    I was going through an article today when it mentioned the following: "We've found many errors over the years. One of the absolute best was the following in the X Window System: if(getuid() != 0 && geteuid == 0) { ErrorF("Only root"); exit(1); } It allowed any local user to get root access. (The tautological check geteuid == 0 was intended to be geteuid() == 0. In its current form, it compress the address of geteuid to 0; given that the function exists, its address is never 0)." The article explained what was wrong with the code but I would like to know what it means to say that "It allowed any local user to get root access". I am not an expert in C but can someone give me an exact context in which this exploit would work? Specifically, what I mean is, lets say I am the local user, how would I get root access if we assume this code to be present somewhere?

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  • Best and easiest algorithm to search for a vertex on a Graph?

    - by Nazgulled
    Hi, After implementing most of the common and needed functions for my Graph implementation, I realized that a couple of functions (remove vertex, search vertex and get vertex) don't have the "best" implementation. I'm using adjacency lists with linked lists for my Graph implementation and I was searching one vertex after the other until it finds the one I want. Like I said, I realized I was not using the "best" implementation. I can have 10000 vertices and need to search for the last one, but that vertex could have a link to the first one, which would speed up things considerably. But that's just an hypothetical case, it may or may not happen. So, what algorithm do you recommend for search lookup? Our teachers talked about Breadth-first and Depth-first mostly (and Dikjstra' algorithm, but that's a completely different subject). Between those two, which one do you recommend? It would be perfect if I could implement both but I don't have time for that, I need to pick up one and implement it has the first phase deadline is approaching... My guess, is to go with Depth-first, seems easier to implement and looking at the way they work, it seems a best bet. But that really depends on the input. But what do you guys suggest?

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  • How is this algorithm, for finding maximum path on a Directed Acyclical Graph, called?

    - by Martín Fixman
    Since some time, I'm using an algorithm that runs in complexity O(V + E) for finding maximum path on a Directed Acyclical Graph from point A to point B, that consists on doing a flood fill to find what nodes are accessible from note A, and how many "parents" (edges that come from other nodes) each node has. Then, I do a BFS but only "activating" a node when I already had used all its "parents". queue <int> a int paths[] ; //Number of paths that go to note i int edge[][] ; //Edges of a int mpath[] ; //max path from 0 to i (without counting the weight of i) int weight[] ; //weight of each node mpath[0] = 0 a.push(0) while not empty(a) for i in edge[a] paths[i] += 1 a.push(i) while not empty(a) for i in children[a] mpath[i] = max(mpath[i], mpath[a] + weight[a]) ; paths[i] -= 1 ; if path[i] = 0 a.push(i) ; Is there any special name for this algorithm? I told it to an Informatics professor, he just called it "Maximum Path on a DAG", but it doesn't sound good when you say "I solved the first problem with a Fenwick Tree, the second with Dijkstra, and the third with Maximum Path".

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  • What algorithm should i follow to retrieve data in the prescribed format?

    - by Prateek
    I have to retrieve data from a database in which tables are consisting of fields like "ttc, rm, atc and lta" namely. Actually these values are stored on daily basis with a 15 min interval like From_time to_time ttc rm atc lta 00:00 00:15 45 10 35 25, 00:15 00:30 35 10 25 25 and so on .. These values are stored for every day of every month and i want it to be previewed in the prescribed format then what algorithm should i follow. I am confused about how to do comparisons for a format like below mentioned. The format is at this link https://drive.google.com/a/itbhu.ac.in/file/d/0B_J0Ljq64i4Za2J1V0lvbDZ4eGc/edit?usp=sharing To be specific once again, my question is, I have to prepare a report from the retrieved data which is being stored in the databases as explained above. But the report which is going to be prepared will be of entire month. So, to say the least, there may be cases that for two particular days the value of "ttc" would be same for some time so i want it to be listed together (as shown in format). And the confusing part is any of the values "ttc", "rm", "atc", "lta" can be same for any particular interval. So what algorithm should i follow for such comparisons. And if still any query with question, u can ask your doubt. Thanks

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  • 2D vector value replacement using classes; genetic algorithm mutation

    - by gcolumbus
    I have a 2D vector as defined by the classes below. Note that I've used classes because I'm trying to program a genetic algorithm such that many, many 2D vectors will be created and they will all be different. class Quad: public std::vector<int> { public: Quad() : std::vector<int>(4,0) {} }; class QuadVec : public std::vector<Quad> { }; An important part of my algorithm, however, is that I need to be able to "mutate" (randomly change) particular values in a certain number of randomly chosen 2D vectors. This has me stumped. I can easily write code to randomly select the value within the 2D vector that will be selected for "mutation" but how do I actually enact that change using classes? I understand how this would be done with one 2D vector that has already been initialized but how do I do this if it hasn't? Please let me know if I haven't provided enough info or am not clear as I tend to do that. Thanks for your time and help!

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