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  • hi question about mathematics

    - by davit-datuashvili
    hi i have one question i know site mathoverflow.com and have posted question but unfortunately no one give me answer if i post here can anybody help me? it is not homework because i know somebody will say it is homework what u have tried but this is not so i dont know how solve please if it is possible i will post here ok?

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  • Fast way to manually mod a number

    - by Nikolai Mushegian
    I need to be able to calculate (a^b) % c for very large values of a and b (which individually are pushing limit and which cause overflow errors when you try to calculate a^b). For small enough numbers, using the identity (a^b)%c = (a%c)^b%c works, but if c is too large this doesn't really help. I wrote a loop to do the mod operation manually, one a at a time: private static long no_Overflow_Mod(ulong num_base, ulong num_exponent, ulong mod) { long answer = 1; for (int x = 0; x < num_exponent; x++) { answer = (answer * num_base) % mod; } return answer; } but this takes a very long time. Is there any simple and fast way to do this operation without actually having to take a to the power of b AND without using time-consuming loops? If all else fails, I can make a bool array to represent a huge data type and figure out how to do this with bitwise operators, but there has to be a better way.

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  • How to find largest common sub-tree in the given two binary search trees?

    - by Bhushan
    Two BSTs (Binary Search Trees) are given. How to find largest common sub-tree in the given two binary trees? EDIT 1: Here is what I have thought: Let, r1 = current node of 1st tree r2 = current node of 2nd tree There are some of the cases I think we need to consider: Case 1 : r1.data < r2.data 2 subproblems to solve: first, check r1 and r2.left second, check r1.right and r2 Case 2 : r1.data > r2.data 2 subproblems to solve: - first, check r1.left and r2 - second, check r1 and r2.right Case 3 : r1.data == r2.data Again, 2 cases to consider here: (a) current node is part of largest common BST compute common subtree size rooted at r1 and r2 (b)current node is NOT part of largest common BST 2 subproblems to solve: first, solve r1.left and r2.left second, solve r1.right and r2.right I can think of the cases we need to check, but I am not able to code it, as of now. And it is NOT a homework problem. Does it look like?

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  • Find a repeated numbers out of 3 boxes

    - by james1
    I have 3 boxes, each box contain 10 piece of numbered paper (1 - 10) but there is a number the same in all 3 boxes eg: box1 has number 4 and box2 has number 4 and box3 also has number 4. How to find that repeated number in java with an efficient/fastest way possible?

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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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  • Display relative time in hour, day, month and year

    - by JohnJohnGa
    I wrote a function toBeautyString(epoch) : String which given a epoch, return a string which will display the relative time from now in hour and minute For instance: // epoch: 1346140800 -> Tue, 28 Aug 2012 05:00:00 GMT // and now: 1346313600 -> Thu, 30 Aug 2012 08:00:00 GMT toBeautyString(1346140800) -> "2 days and 3 hours ago" I want now to extend this function to month and year, so it will be able to print: 2 years, 1 month, 3 days and 1 hour ago Only with epoch without any external libraries. The purpose of this function is to give to the user a better way to visualize the time in the past. I found this: Calculating relative time but the granularity is not enough.

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  • Way to store a large dictionary with low memory footprint + fast lookups (on Android)

    - by BobbyJim
    I'm developing an android word game app that needs a large (~250,000 word dictionary) available. I need: reasonably fast look ups e.g. constant time preferable, need to do maybe 200 lookups a second on occasion to solve a word puzzle and maybe 20 lookups within 0.2 second more often to check words the user just spelled. EDIT: Lookups are typically asking "Is in the dictionary?". I'd like to support up to two wildcards in the word as well, but this is easy enough by just generating all possible letters the wildcards could have been and checking the generated words (i.e. 26 * 26 lookups for a word with two wildcards). as it's a mobile app, using as little memory as possible and requiring only a small initial download for the dictionary data is top priority. My first naive attempts used Java's HashMap class, which caused an out of memory exception. I've looked into using the SQL lite databases available on android, but this seems like overkill. What's a good way to do what I need?

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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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  • What's the "Hello World!" of genetic algorithms good for?

    - by JohnIdol
    I found this very cool C++ sample , literally the "Hello World!" of genetic algorithms. I so decided to re-code the whole thing in C# and this is the result. Now I am asking myself: is there any practical application along the lines of generating a target string starting from a population of random strings? EDIT: my buddy on twitter just tweeted that "is useful for transcription type things such as translation. Does not have to be Monkey's". I wish I had a clue.

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  • Latex: vertical line in lstlistings

    - by Helltone
    I want to have a vertical line for indentation in the lstlisting environment, similar to what one can get in algorithm2e. I tried doing something like the code below, but the the |'s are not contiguous and the result is ugly. \lstset{ ... showtabs=true, tabsize=3, tab=\hfill$|$\hfill, ... }

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  • Reverse engineering a bezier curve

    - by Martin
    Given a few sample points on a bézier curve, is it possible to work out the set of possible parameters of the curve? In my specific application there is a limited set of endpoints the curve may have, so I want to generate the set of possible curves, enumerate all of them and pick out all the ones which may end on a valid end point.

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  • Could I do this blind relative to absolute path conversion (for perforce depot paths) better?

    - by wonderfulthunk
    I need to "blindly" (i.e. without access to the filesystem, in this case the source control server) convert some relative paths to absolute paths. So I'm playing with dotdots and indices. For those that are curious I have a log file produced by someone else's tool that sometimes outputs relative paths, and for performance reasons I don't want to access the source control server where the paths are located to check if they're valid and more easily convert them to their absolute path equivalents. I've gone through a number of (probably foolish) iterations trying to get it to work - mostly a few variations of iterating over the array of folders and trying delete_at(index) and delete_at(index-1) but my index kept incrementing while I was deleting elements of the array out from under myself, which didn't work for cases with multiple dotdots. Any tips on improving it in general or specifically the lack of non-consecutive dotdot support would be welcome. Currently this is working with my limited examples, but I think it could be improved. It can't handle non-consecutive '..' directories, and I am probably doing a lot of wasteful (and error-prone) things that I probably don't need to do because I'm a bit of a hack. I've found a lot of examples of converting other types of relative paths using other languages, but none of them seemed to fit my situation. These are my example paths that I need to convert, from: //depot/foo/../bar/single.c //depot/foo/docs/../../other/double.c //depot/foo/usr/bin/../../../else/more/triple.c to: //depot/bar/single.c //depot/other/double.c //depot/else/more/triple.c And my script: begin paths = File.open(ARGV[0]).readlines puts(paths) new_paths = Array.new paths.each { |path| folders = path.split('/') if ( folders.include?('..') ) num_dotdots = 0 first_dotdot = folders.index('..') last_dotdot = folders.rindex('..') folders.each { |item| if ( item == '..' ) num_dotdots += 1 end } if ( first_dotdot and ( num_dotdots > 0 ) ) # this might be redundant? folders.slice!(first_dotdot - num_dotdots..last_dotdot) # dependent on consecutive dotdots only end end folders.map! { |elem| if ( elem !~ /\n/ ) elem = elem + '/' else elem = elem end } new_paths << folders.to_s } puts(new_paths) end

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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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  • How to find out top links in a website?

    - by Anil
    I want to know what are the best links in a site are? It may be pagerank wise or popularity wise. For example http://www.pragprog.com is a site. I want to find out what are the most relevant links this site has. The links should not be external pointing links. It should be of the same site. Do google or any similar site can tell such information?

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  • Five unique, random numbers from a subset

    - by tau
    I know similar questions come up a lot and there's probably no definitive answer, but I want to generate five unique random numbers from a subset of numbers that is potentially infinite (maybe 0-20, or 0-1,000,000). The only catch is that I don't want to have to run while loops or fill an array. My current method is to simply generate five random numbers from a subset minus the last five numbers. If any of the numbers match each other, then they go to their respective place at the end of the subset. So if the fourth number matches any other number, it will bet set to the 4th from the last number. Does anyone have a method that is "random enough" and doesn't involve costly loops or arrays? Please keep in mind this a curiosity, not some mission-critical problem. I would appreciate it if everyone didn't post "why are you having this problem?" answers. I am just looking for ideas. Thanks a lot!

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  • Constructing colours for maximum contrast

    - by Martin
    I want to draw some items on screen, each item is in one of N sets. The number of sets changes all the time, so I need to calculate N different colours which are as different as possible (to make it easy to identify what is in which set). So, for example with N = 2 my results would be black and white. With three I guess I would get all red, all green, all blue. For all four, it's less obvious what the correct answer is, and this is where I'm having trouble.

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  • question about LSD radix sort

    - by davit-datuashvili
    hello i have following code public class LSD{ public static int R=1<<8; public static int bytesword=4; public static void radixLSD(int a[],int l,int r){ int aux[]=new int[a.length]; for (int d=bytesword-1;d>=0;d--){ int i, j; int count[]=new int[R+1]; for ( j=0;j<R;j++) count[j]=0; for (i=l;i<=r;i++) count[digit(a[i],d)+1]++; for (j=1;j<R;j++) count[j]+=count[j-1]; for (i=l;i<=r;i++) aux[count[digit(a[i],d)]++]=a[i]; for (i=l;i<=r;i++) a[i]=aux[i-1]; } } public static void main(String[]args){ int a[]=new int[]{3,6,5,7,4,8,9}; radixLSD(a,0,a.length-1); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static int digit(int n,int d){ return (n>>d)&1; } } but it show me mistake java.lang.ArrayIndexOutOfBoundsException: -1 at LSD.radixLSD(LSD.java:19) at LSD.main(LSD.java:29) please help me

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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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  • 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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  • A balanced binary search tree which is also a heap

    - by saeedn
    I'm looking for a data structure where each element in it has two keys. With one of them the structure is a BST and looking at the other one, data structure is a heap. With a little search, I found a structure called Treap. It uses the heap property with a random distribution on heap keys to make the BST balanced! What I want is a Balanced BST, which can be also a heap. The BST in Treap could be unbalanced if I insert elements with heap Key in the order of my choice. Is there such a data structure?

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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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  • Fast dot product for a very special case

    - by psihodelia
    Given a vector X of size L, where every scalar element of X is from a binary set {0,1}, it is to find a dot product z=dot(X,Y) if vector Y of size L consists of the integer-valued elements. I suggest, there must exist a very fast way to do it. Let's say we have L=4; X[L]={1, 0, 0, 1}; Y[L]={-4, 2, 1, 0} and we have to find z=X[0]*Y[0] + X[1]*Y[1] + X[2]*Y[2] + X[3]*Y[3] (which in this case will give us -4). It is obvious that X can be represented using binary digits, e.g. an integer type int32 for L=32. Then, all what we have to do is to find a dot product of this integer with an array of 32 integers. Do you have any idea or suggestions how to do it very fast?

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