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  • Explanation needed for sum of prime below n numbers

    - by Bala Krishnan
    Today I solved a problem given in Project Euler its problem no 10 and it took 7 hrs for my python program to show the result. But in that forum itself a person named lassevk posted solution for this and it took only 4 sec. And its not possible for me to post this question in that forum because its not discussion forum. So, think about this if you want to mark this question as non-constructive. marked = [0] * 2000000 value = 3 s = 2 while value < 2000000: if marked[value] == 0: s += value i = value while i < 2000000: marked[i] = 1 i += value value += 2 print s If any one understand this code please explain it simple as possible. Link to the Problem 10 question.

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  • Load balancing and shedulling algorithms .NET

    - 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 approx. each job will take to be caclulated. Also I have priorities. My question is how to keep all machines loaded 99-100% and shedule the jobs in the best way. Each machine can do several calculations at the time. Jobs are pushed to the machine. Central machine knows current load of each machine. Also I would like to to assign some king of machine learning here, because I will know statistics of each job (started, finished, cpu load etc.). How to distribute jobs(calculations) in the best possible way, also keep in mind priority. Any suggestions ? Ideas ? Algorithms ?

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  • Reverse regular expressions to generate data

    - by Anton Gogolev
    In one of the StackOverflow Podcasts (the one where guys were discussing data generation for testing DBs -- either #11 or #12), Jeff mentioned something like "reverse regular expressions", which are used exactly for that purpose: given a regex, produce a string which will eventually match said regex. What is the correct term for this whole concept? Is this a well-known concept?

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  • Is there a good radixsort-implementation for floats in C#

    - by CommuSoft
    I have a datastructure with a field of the float-type. A collection of these structures needs to be sorted by the value of the float. Is there a radix-sort implementation for this. If there isn't, is there a fast way to access the exponent, the sign and the mantissa. Because if you sort the floats first on mantissa, exponent, and on exponent the last time. You sort floats in O(n).

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  • C++ priority queue structure used ?

    - by John Retallack
    While searching for some functions in C++ STL documentation I read that push and pop for priority queues needs constant time. "Constant (in the priority_queue). Although notice that push_heap operates in logarithmic time." My question is what kind of data structure is used to mantain a priority queue with O(1) for push and pop ?

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  • Given an even number of vertices, how to find an optimum set of pairs based on proximity?

    - by Alex Z
    The problem: We have a set of n vertices in 3D euclidean space, and there is an even number of these vertices. We want to pair them up based on their proximity. In other words, we'd like to be able to find a set of vertex pairs, where the vertices in each pair are as close as possible together. We want to minimise sacrificing the proximity between the vertices of any other pairs as much as possible in doing this. I am not looking for the most optimal solution (if it even strictly exists/can be done), just a reasonable one that can be computed relatively quickly. A relatively awful brute force approach involves choosing a vertex and looping through the rest to find its nearest neighbor and then repeating until there are none left. Of course as we near the end of the list the closest vertex could be very far away, but it is the only choice, therefore this can fail badly on the third point above.

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  • Find common nodes from two linked lists using recursion

    - by Dan
    I have to write a method that returns a linked list with all the nodes that are common to two linked lists using recursion, without loops. For example, first list is 2 - 5 - 7 - 10 second list is 2 - 4 - 8 - 10 the list that would be returned is 2 - 10 I am getting nowhere with this.. What I have been think of was to check each value of the first list with each value of the second list recursively but the second list would then be cut by one node everytime and I cannot compare the next value in the first list with the the second list. I hope this makes sense... Can anyone help?

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  • Are there Adaptive Replacement Cache patent-free alternatives?

    - by aleccolocco
    An open source high-performance project I'm working on needs to keep a cache of parsed/compiled files. A plain LRU or a plain LFU wouldn't fit. Plain LRU wouldn't work as there will be remote batch/spider processes hitting the service regularly. Plain LFU wouldn't work because content will age. ARC seems like the perfect solution but since IBM holds patents to it at least one open source project dropped it. Are there any (good enough) alternatives? EDIT: I'm not looking for exactly the same thing, just something that could handle those two situations. Perhaps some simple strategy with timestamps and sources. There have to be many programmers who faced this situation before. That's why the "good enough" bit.

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  • Whats the best data-structure for storing 2-tuple (a, b) which support adding, deleting tuples and c

    - by bhups
    Hi So here is my problem. I want to store 2-tuple (key, val) and want to perform following operations: - keys are strings and values are Integers - multiple keys can have same value - adding new tuples - updating any key with new value (any new value or updated value is greater than the previous one, like timestamps) - fetching all the keys with values less than or greater than given value - deleting tuples. Hash seems to be the obvious choice for updating the key's value but then lookups via values will be going to take longer (O(n)). The other option is balanced binary search tree with key and value switched. So now lookups via values will be fast (O(lg(n))) but updating a key will take (O(n)). So is there any data-structure which can be used to address these issues? Thanks.

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  • Effecient data structure design

    - by Sway
    Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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  • Simple/Basic steganography algorithms and methods

    - by tomp
    What are the basic and simpliest steganography algorithms and methods? I mean the steganography applied to images. How does simple program that hides data to images work? How does the program recognize the encrypted message in image without the source image? What are the main techniques used?

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  • Javascript Number Random Scrambler

    - by stjowa
    Hi, I need a Javascript random number scrambler for my website. Seems simple, but I can not figure out how to do it. Can anyone help me out? I have the following array of numbers: 1 2 3 4 5 6 7 8 9 I would like to be able to have these numbers scrambled randomly. Like the following: 3 6 4 2 9 5 1 8 7 or 4 1 7 3 5 9 2 6 8 So, specifically, I would like a function that takes in an array of numbers (1 - n) and then returns that same array of numbers - scrambled randomly with different calls to the function. Maybe a noob function, but can't seem to figure it out. Thanks!

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  • Facebook Hacker Cup: Power Overwhelming

    - by marcog
    A lot of people at Facebook like to play Starcraft II™. Some of them have made a custom game using the Starcraft II™ map editor. In this game, you play as the noble Protoss defending your adopted homeworld of Shakuras from a massive Zerg army. You must do as much damage to the Zerg as possible before getting overwhelmed. You can only build two types of units, shield generators and warriors. Shield generators do no damage, but your army survives for one second per shield generator that you build. Warriors do one damage every second. Your army is instantly overrun after your shield generators expire. How many shield generators and how many warriors should you build to inflict the maximum amount of damage on the Zerg before your army is overrun? Because the Protoss value bravery, if there is more than one solution you should return the one that uses the most warriors. Constraints 1 = G (cost for one shield generator) = 100 1 = W (cost for one warrior) = 100 G + W = M (available funds) = 1000000000000 (1012)

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  • BFS algorithm problem

    - by Gorkamorka
    The problem is as follows: A wanderer begins on the grid coordinates (x,y) and wants to reach the coordinates (0,0). From every gridpoint, the wanderer can go 8 steps north OR 3 steps south OR 5 steps east OR 6 steps west (8N/3S/5E/6W). How can I find the shortest route from (X,Y) to (0,0) using breadth-first search? Clarifications: Unlimited grid Negative coordinates are allowed A queue (linked list or array) must be used No obstacles present

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  • How to compute palindrome from a stream of characters in sub-linear space/time?

    - by wrick
    I don't even know if a solution exists or not. Here is the problem in detail. You are a program that is accepting an infinitely long stream of characters (for simplicity you can assume characters are either 1 or 0). At any point, I can stop the stream (let's say after N characters were passed through) and ask you if the string received so far is a palindrome or not. How can you do this using less sub-linear space and/or time.

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  • Why can't RB-Tree be a list?

    - by Alex
    Hey everyone. I have a problem with the rb-trees. according to wikipedia, rb-tree needs to follow the following: A node is either red or black. The root is black. (This rule is used in some definitions and not others. Since the root can always be changed from red to black but not necessarily vice-versa this rule has little effect on analysis.) All leaves are black. Both children of every red node are black. Every simple path from a given node to any of its descendant leaves contains the same number of black nodes. As we know, an rb-tree needs to be balanced and has the height of O(log(n)). But, if we insert an increasing series of numbers (1,2,3,4,5...) and theoretically we will get a tree that will look like a list and will have the height of O(n) with all its nodes black, which doesn't contradict the rb-tree properties mentioned above. So, where am I wrong?? thanks.

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  • Count Occurence of Needle String in Haystack String, most optimally?

    - by Taranfx
    The Problem is simple Find "ABC" in "ABCDSGDABCSAGAABCCCCAAABAABC" Here is the solution I propose, I'm looking for any solutions that might be better than this one. public static void main(String[] args) { String haystack = "ABCDSGDABCSAGAABCCCCAAABAABC"; String needle = "ABC"; char [] needl = needle.toCharArray(); int needleLen = needle.length(); int found=0; char hay[] = haystack.toCharArray(); int index =0; int chMatched =0; for (int i=0; i<hay.length; i++){ if (index >= needleLen || chMatched==0) index=0; System.out.print("\nchar-->"+hay[i] + ", with->"+needl[index]); if(hay[i] == needl[index]){ chMatched++; System.out.println(", matched"); }else { chMatched=0; index=0; if(hay[i] == needl[index]){ chMatched++; System.out.print("\nchar->"+hay[i] + ", with->"+needl[index]); System.out.print(", matched"); }else continue; } if(chMatched == needleLen){ found++; System.out.println("found. Total ->"+found); } index++; } System.out.println("Result Found-->"+found); } It took me a while creating this one. Can someone suggest a better solution (if any) P.S. Drop the sysouts if they look messy to you.

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  • Python - Compress Ascii String

    - by n0idea
    I'm looking for a way to compress an ascii-based string, any help? I need also need to decompress it. I tried zlib but with no help. What can I do to compress the string into lesser length? code: def compress(request): if request.POST: data = request.POST.get('input') if is_ascii(data): result = zlib.compress(data) return render_to_response('index.html', {'result': result, 'input':data}, context_instance = RequestContext(request)) else: result = "Error, the string is not ascii-based" return render_to_response('index.html', {'result':result}, context_instance = RequestContext(request)) else: return render_to_response('index.html', {}, context_instance = RequestContext(request))

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