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  • Simple Python Challenge: Fastest Bitwise XOR on Data Buffers

    - by user213060
    Challenge: Perform a bitwise XOR on two equal sized buffers. The buffers will be required to be the python str type since this is traditionally the type for data buffers in python. Return the resultant value as a str. Do this as fast as possible. The inputs are two 1 megabyte (2**20 byte) strings. The challenge is to substantially beat my inefficient algorithm using python or existing third party python modules (relaxed rules: or create your own module.) Marginal increases are useless. from os import urandom from numpy import frombuffer,bitwise_xor,byte def slow_xor(aa,bb): a=frombuffer(aa,dtype=byte) b=frombuffer(bb,dtype=byte) c=bitwise_xor(a,b) r=c.tostring() return r aa=urandom(2**20) bb=urandom(2**20) def test_it(): for x in xrange(1000): slow_xor(aa,bb)

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  • number of days in a period that fall within another period

    - by thomas
    I have 2 independent but contiguous date ranges. The first range is the start and end date for a project. Lets say start = 3/21/10 and end = 5/16/10. The second range is a month boundary (say 3/1/10 to 3/31/10, 4/1/10 to 4/30/10, etc.) I need to figure out how many days in each month fall into the first range. The answer to my example above is March = 10, April = 30, May = 16. I am trying to figure out an excel formula or VBA function that will give me this value. Any thoughts on an algorithm for this? I feel it should be rather easy but I can't seem to figure it out. I have a formula which will return TRUE/FALSE if ANY part of the month range is within the project start/end but not the number of days. That function is below. return month_start <= project_end And month_end >= project_start

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  • New to AVL tree implementation.

    - by nn
    I am writing a sliding window compression algorithm (LZ77) that searches for phrases in a "moving" dictionary. So far I have written a BST where each node is stored in an array and it's index in the array is also the value of the starting position in the window itself. I am now looking at transforming the BST to an AVL tree. I am a little confused at the sample implementations I have seen. Some only appear to store the balance factors whereas others store the height of each tree. Are there any performance advantage/disadvantages of storing the height and/or balance factor for each node? Apologies if this is a very simple question, but I'm still not visualizing how I want to restructure my BST to implement height balancing. Thanks.

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  • Minimizing the number of boxes that cover a given set of intervals

    - by fortran
    Hi, this is a question for the algorithms gurus out there :-) Let S be a set of intervals of the natural numbers that might overlap and b a box size. Assume that for each interval, the range is strictly less than b. I want to find the minimum set of intervals of size b (let's call it M) so all the intervals in S are contained in the intervals of M. Trivial example: S = {[1..4], [2..7], [3..5], [8..15], [9..13]} b = 10 M = {[1..10], [8..18]} // so ([1..4], [2..7], [3..5]) are inside [1..10] and ([8..15], [9..13]) are inside [8..18] I think a greedy algorithm might not work always, so if anybody knows of a solution of this problem (or a similar one that can be converted into), that would be great. Thanks!

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  • What are some good algorithms for drawing lines between graph nodes?

    - by ApplePieIsGood
    What I'm specifically grappling with is not just the layout of a graph, but when a user selects a graph node and starts to drag it around the screen area, the line has to constantly be redrawn to reflect what it would look like if the user were to release the node. I suppose this is part of the layout algorithm? Also some applications get a bit fancy and don't simply draw the line in a nice curvy way, but also bend the line around the square shaped node in almost right angles. See attached image and keep in mind that as a node is dragged, the line is drawn as marching ants, and re-arranged nicely, while retaining its curved style.

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  • How to calculate order (big O) for more complex algorithms (ie quicksort)

    - by bangoker
    I know there are quite a bunch of questions about big O notation, I have already checked Plain english explanation of Big O , Big O, how do you calculate/approximate it?, and Big O Notation Homework--Code Fragment Algorithm Analysis?, to name a few. I know by "intuition" how to calculate it for n, n^2, n! and so, however I am completely lost on how to calculate it for algorithms that are log n , n log n, n log log n and so. What I mean is, I know that Quick Sort is n log n (on average).. but, why? Same thing for merge/comb, etc. Could anybody explain me in a not to math-y way how do you calculate this? The main reason is that Im about to have a big interview and I'm pretty sure they'll ask for this kind of stuff. I have researched for a few days now, and everybody seem to have either an explanation of why bubble sort is n^2 or the (for me) unreadable explanation a la wikipedia Thanks!

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  • count of distinct acyclic paths from A[a,b] to A[c,d]?

    - by Sorush Rabiee
    I'm writing a sokoban solver for fun and practice, it uses a simple algorithm (something like BFS with a bit of difference). now i want to estimate its running time ( O and omega). but need to know how to calculate count of acyclic paths from a vertex to another in a network. actually I want an expression that calculates count of valid paths, between two vertices of a m*n matrix of vertices. a valid path: visits each vertex 0 or one times. have no circuits for example this is a valid path: but this is not: What is needed is a method to find count of all acyclic paths between the two vertices a and b. comments on solving methods and tricks are welcomed.

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  • How to create a random string of characters in C#?

    - by Keltex
    I'm trying to create random strings of characters. I'm wondering if there might be a more efficient way. Here's my algorithm: string RANDOM = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#@$^*()"; StringBuilder sb = new StringBuilder(); int length = rand.Next(10) + 1; for (int idx = 0; idx < length; ++idx) { sb.Append(RANDOM[rand.Next(RANDOM.Length)]); } string RandomString = sb.ToString(); I'm wondering if the StringBuilder is the best choice. Also if selecting a random character from my RANDOM string is the best way.

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  • Finding backedges in a graph, with special conditions.

    - by Morteza M.
    There is a vertex v, such that from the subtree rooted at v, there are at least two backedges to proper ancestors of v. The problem is finding whether such backedges exist or not ( finding v is not important at all). I run DFS algorithm, I can find backedges and save them in an array. I know which backedges in this array belong to a common tree. but I have problem on matching this condition in O(E) time. can anyone help me with that?

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  • Matlab postpones disp calls when doing demanding calculations why is that?

    - by Reed Richards
    I am implementing an algorithm in Matlab. Among other things it calculates shortest paths etc. so its quite demanding for my old computer. I've put out disp calls through out the program to see what's happening all the time. However when starting on a particulary heavy for loop the disp seemes not to be called until the loop is over even though it comes before the loop. Why is that? I though that Matlab was really linear or am I just choking it with to many calculations and the disp calls get the lowest priority?

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  • Algorithms to find longest common prefix in a sliding window.

    - by nn
    Hi, I have written a Lempel Ziv compressor and decompressor. I am seeking to improve the time to search the dictionary for a phrase. I have considered K-M-P and Boyer-Moore, but I think an algorithm that adapts to changes in the dictionary would be faster. I've been reading that binary search trees (AVL or with splays) improve the performance of compression time considerably. What I fail to understand is how to bootstrap the binary search tree and insert/remove data. I'm not actually quite sure the significance of each node in the binary search. I am searching for phrases so will each character be considered a node? Also how and what is inserted/removed from the search tree as new data enters the dictionary and old data is removed? The binary search tree sounds like a good payoff since it can adapt to the dictionary, but I'm just not quite sure of how it's used.

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  • Algorithm for Source Control System?

    - by Michael Stum
    I need to write a simple source control system and wonder what algorithm I would use for file differences? I don't want to look into existing source code due to license concerns. I need to have it licensed under MPL so I can't look at any of the existing systems like CVS or Mercurial as they are all GPL licensed. Just to give some background, I just need some really simple functions - binary files in a folder. no subfolders and every file behaves like it's own repository. No Metadata except for some permissions. Overall really simple stuff, my single concern really is how to store only the differences of a file from revision to revision without wasting too much space but also without being too inefficient (Maybe store a full version every X changes, a bit like Keyframes in Videos?)

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  • Evaluating a function at a particular value in parallel

    - by Gaurav Kalra
    Hi. The question may seem vague, but let me explain it. Suppose we have a function f(x,y,z ....) and we need to find its value at the point (x1,y1,z1 .....). The most trivial approach is to just replace (x,y,z ...) with (x1,y1,z1 .....). Now suppose that the function is taking a lot of time in evaluation and I want to parallelize the algorithm to evaluate it. Obviously it will depend on the nature of function, too. So my question is: what are the constraints that I have to look for while "thinking" to parallelize f(x,y,z...)? If possible, please share links to study.

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  • Counting problem: possible sudoko tables?

    - by Sorush Rabiee
    Hi, I'm working on a sudoko solver. my method is using a game tree and explore possible permutations for each set of digits by DFS Algorithm. in order to analyzing problem, i want to know what is the count of possible valid and invalid sudoko tables? - a 9*9 table that have 9 one, 9 two, ... , 9 nine. (this isn't exact duplicate by this question) my solution is: 1- First select 9 cells for 1s: (*) 2- and like (1) for other digits (each time, 9 cells will be deleted from remaining available cells): C(81-9,9) , C(81-9*2,9) .... = 3- finally multiply the result by 9! (permutation of 123456789 in (*)) this is not equal to accepted answer of this question but problems are equivalent. what did i do wrong?

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  • How to improve performance

    - by Ram
    Hi, In one of mine applications I am dealing with graphics objects. I am using open source GPC library to clip/merge two shapes. To improve accuracy I am sampling (adding multiple points between two edges) existing shapes. But before displaying back the merged shape I need to remove all the points between two edges. But I am not able to find an efficient algorithm that will remove all points between two edges which has same slope with minimum CPU utilization. Currently all points are of type PointF Any pointer on this will be a great help.

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  • Finding recurrence relations of an algorithm

    - by Roarke
    I'm reading my algorithms text book, and I'm reading about recurrence relations and finding the algorithms big O complexity. I run across this line "In the case of the merge-sort algorithm, we get the recurrence equation: t(n) = b if n < 2 = 2t(n/2) +bn if n >= 2 for b > 0 my response was "how the heck did we know that?!?!" So i'm wondering if there is a systematic approach, or just a logical way of getting these recurrence relations from the algorithms can some one explain where the b and the two 2's come from?

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  • Algorithm for Search page

    - by Geetha
    Hi All, I am creating a search page where we can find the product by entering the text. ex: Brings on the night. My query bring the records which contain atleast word from this. Needs: 1. First row should contains the record with the given sentence. 2. Second most matching....etc How to achieve this. Is there any algorithm for this. It will be more helpful if anyone share your idea. Geetha

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  • List of generic algorithms and data structures

    - by Jake Petroules
    As part of a library project, I want to include a plethora of generic algorithms and data structures. This includes algorithms for searching and sorting, data structures like linked lists and binary trees, path-finding algorithms like A*... the works. Basically, any generic algorithm or data structure you can think of that you think might be useful in such a library, please post or add it to the list. Thanks! (NOTE: Because there is no single right answer I've of course placed this in community wiki... and also, please don't suggest algorithms which are too specialized to be provided by a generic library) The List: Data structures AVL tree B-tree B*-tree B+-tree Binary tree Binary heap Binary search tree Linked lists Singly linked list Doubly linked list Stack Queue Sorting algorithms Binary tree sort Bubble sort Heapsort Insertion sort Merge sort Quicksort Selection sort Searching algorithms

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  • Task management algorithm in C#

    - by silverwizz
    Hi guys, i am looking for efficient task management fo C# what i mean by task management is executing pre-defined interval time of task. Example: task a needs to be run every 1 mins task b needs to be run every 3 mins task c needs to be run every 5 mins these tasks can be added and removed in arbitary time... And the task that i mentioned can be 100000 or more... The task will bw executed forever until it is removed... Do u guys familiar with this kind of algorithm? I am thinking to implement in either c# or php.... Thanks

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  • The sieve of Eratosthenes in F#

    - by IVlad
    I am interested in an implementation of the sieve of eratosthenes in purely functional F#. I am interested in an implementation of the actual sieve, not the naive functional implementation that isn't really the sieve, so not something like this: let rec PseudoSieve list = match list with | hd::tl -> hd :: (PseudoSieve <| List.filter (fun x -> x % hd <> 0) tl) | [] -> [] The second link above briefly describes an algorithm that would require the use of a multimap, which isn't available in F# as far as I know. The Haskell implementation given uses a map that supports an insertWith method, which I haven't seen available in the F# functional map. Does anyone know a way to translate the given Haskell map code to F#, or perhaps knows of alternative implementation methods or sieving algorithms that are as efficient and better suited for a functional implementation or F#?

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  • Scale image to completely fill bounding box

    - by Larsenal
    For instance, if I need to fill a bounding box that is 100px wide by 50px tall, the following input images would have the following behavior: 200w x 200h gets scaled down 50% and 25% gets chopped off the top and bottom. 200w x 100h gets scaled down 50% with no cropping. 100w x 200h gets is not scaled, but 75px get chopped off top and bottom. This seems like it'd be a common resizing function, but I haven't been able to track down an example of the algorithm. Will accept answer in any language including pseudo code. A link to a page with the answer is great too!

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  • Rerversing AND Bitwise.

    - by Benjamin
    Hey all, Here's the following algorithm: int encryption(int a, int b) { short int c, c2; uint8_t d; c = a ^ b; c2 = c; d = 0; while(c) { c &= c - 1; d++; } return d; } How can I find which variable a and b I should send in that function to decide of the output value of d? In other words, how can I reverse the algoritm to let's say if I want d=11?

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  • I need to stop execution during recursive algorithm

    - by Shaza
    Hey, I have a problem in choosing the right method to accomplish my goal. I'm working on Algorithms teaching system, I'm using C#. I need to divide my algorithm into steps, each step will contain a recursion. I have to stop execution after each step, user can then move to the next step(next recursion) using a button in my GUI. After searching, threads was the right choice, but I found several methods: (Thread.sleep/interrupt): didn't work, my GUI freezed !! (Suspend/Resume): I've read that it's a bad idea to use. (Waithandles): still reading about them. (Monitor wait/resume). I don't have much time to try and read all previous methods, please help me in choosing the best method that fits my system.Any suggestions are extremal welcomed.

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  • Factorial Algorithms in different languages

    - by Brad Gilbert
    I want to see all the different ways you can come up with, for a factorial subroutine, or program. The hope is that anyone can come here and see if they might want to learn a new language. Ideas: Procedural Functional Object Oriented One liners Obfuscated Oddball Bad Code Polyglot Basically I want to see an example, of different ways of writing an algorithm, and what they would look like in different languages. Please limit it to one example per entry. I will allow you to have more than one example per answer, if you are trying to highlight a specific style, language, or just a well thought out idea that lends itself to being in one post. The only real requirement is it must find the factorial of a given argument, in all languages represented. Be Creative! Recommended Guideline: # Language Name: Optional Style type - Optional bullet points Code Goes Here Other informational text goes here I will ocasionally go along and edit any answer that does not have decent formatting.

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  • JQuery/JavaScript div tag "containment" approach/algorithm?

    - by Pete Alvin
    Background: I've created an online circuit design application where div tags are containers that contain smaller div containers and so forth. Question: For any particular div tag I need to quickly identify if it contains other div tags (that may in turn contain other div tags). I've searched JQuery and I don't see any built-in routine for this. Does anyone know of an algorithm that's quicker than O(n^2)? Seems like I have to walk the list of div tags in an outer loop (n) and have an inner loop (another n) to compare against all other div tags and do a "containment test" (position, width, height), building a list of contained div tags. That's n-squared. Then I have to build a list of all nested div tags by concatenating contained lists. So the total would be O(n^2)+n. There must be a better way?

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