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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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  • 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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  • 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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  • Efficient Array Storage for Binary Tree

    - by Sundararajan S
    We have to write the nodes of a binary tree to a file. What is the most space efficient way of writing a binary tree . We can store it in array format with parent in position 'i' and its childs in 2i,2i+1. But this will waste lot of space in case of sparse binary trees.

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  • Removing elements from heap

    - by user193138
    I made a heap. I am curious if there's something subtley wrong with my remove function: int Heap::remove() { if (n == 0) exit(1); int temp = arr[0]; arr[0] = arr[--n]; heapDown(0); arr[n] = 0; return temp; } void Heap::heapDown(int i) { int l = left(i); int r = right(i); // comparing parent to left/right child // each has an inner if to handle if the first swap causes a second swap // ie 1 -> 3 -> 5 // 3 5 1 5 1 3 if (l < n && arr[i] < arr[l]) { swap(arr[i], arr[l]); heapDown(l); if (r < n && arr[i] < arr[r]) { swap(arr[i], arr[r]); heapDown(r); } } else if (r < n && arr[i] < arr[r]) { swap(arr[i], arr[r]); heapDown(r); if (l < n && arr[i] < arr[l]) { swap(arr[i], arr[l]); heapDown(l); } } } Here's my output i1i2i3i4i5i6i7 p Active heap: 7 4 6 1 3 2 5 r Removed 7 r Removed 6 p Active heap: 5 3 4 1 2 Here's my teacher's sample output: p Active heap : 7 4 6 1 3 2 5 r Removed 7 r Removed 6 p Active heap : 5 4 2 1 3 s Heapsorted : 1 2 3 4 5 While our outputs are completely different, I do seem to hold maxheap principle of having everything left oriented and for all nodes parent child(in every case I tried). I try to do algs like this from scratch, so maybe I'm just doing something really weird and wrong (I would only consider it "wrong" if it's O(lg n), as removes are intended to be for heaps). Is there anything in particular "wrong" about my remove? Thanks, http://ideone.com/PPh4eQ

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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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  • PHP Modify Array

    - by Ozzy
    Hi all, I have the following array: array(a, a, a, b, b, c, c, c, c, d, d); When I loop through it and echo it, the result is: a a a b b c c c c d d How ever I want to echo it in such a way that it displays: a b c d a b c d a c c Here is the array in a grid to better explain what im trying to achieve Current a a a b b c c c c d d What im tryin to do a b c d a b c d a c c How would I do this?

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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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  • Count subset of binary pattern ..

    - by mr.bio
    Hi there . I have a A=set of strings and a B=seperate string. I want to count the number of occurences in from B in A. Example : A: 10001 10011 11000 10010 10101 B: 10001 result would be 3.(10001 is a subset of 10001,10011,10101) So i need a function that takes a set and string and returns an int. int myfunc(set<string> , string){ int result; // My Brain is melting return result ; }

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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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  • K-Means Algorithm and java code

    - by Thandar
    Hi all, I need to calculate for grouping objects according to their size. I got k-means algorithms in java which calculate mostly for classifying according to their two or more features and the results are not satisfy for me.I only want to calculate for grouping objects based on one feature.Pseudocode or code would be helpful, too. Thanks u all for helping.

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  • Binary search in rotated sorted list

    - by Algorist
    I am having a sorted list which is rotated and I would like to do a binary search on that list to find the minimum element. Lets suppose initial list is {1,2,3,4,5,6,7,8} rotated list can be like {5,6,7,8,1,2,3,4} Normal binary search doesn't work in this case. Any idea how to do this.

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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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  • Client-server synchronization pattern / algorithm?

    - by tm_lv
    I have a feeling that there must be client-server synchronization patterns out there. But i totally failed to google up one. Situation is quite simple - server is the central node, that multiple clients connect to and manipulate same data. Data can be split in atoms, in case of conflict, whatever is on server, has priority (to avoid getting user into conflict solving). Partial synchronization is preferred due to potentially large amounts of data. Are there any patterns / good practices for such situation, or if you don't know of any - what would be your approach? Below is how i now think to solve it: Parallel to data, a modification journal will be held, having all transactions timestamped. When client connects, it receives all changes since last check, in consolidated form (server goes through lists and removes additions that are followed by deletions, merges updates for each atom, etc.). Et voila, we are up to date. Alternative would be keeping modification date for each record, and instead of performing data deletes, just mark them as deleted. Any thoughts?

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  • longest common subsequence

    - by davit-datuashvili
    i have following code public class LCS1 { public static String lcs(String a,String b) { String x; String y; int alen=a.length(); int blen=b.length(); if (alen==0 || blen==0) { return ""; } else if (a.charAt(alen-1)==b.charAt(blen-1)) { return lcs(a.substring(0,alen-1),b.substring(0,blen-1)); } else { x=lcs(a,b.substring(0,blen-1)); y=lcs(a.substring(0,alen-1),b); } return (x.length()>y.length()) ? x : y; } public static void main(String[]args){ String a="computer"; String b="houseboat"; System.out.println(lcs(a,b)); } } it should return "out" but returns nothing what is problem?

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  • Echo mysql results in a loop?

    - by Roy D. Porter
    I am using turn.js to make a book. Every div within the 'deathnote' div becomes a new page. <div id="deathnote"> //starts book <div style="background-image:url(images/coverpage.jpg);"></div> //creates new page <div style="background-image:url(images/paper.jpg);"></div> //creates new page <div style="background-image:url(images/paper.jpg);"></div> //creates new page </div> //ends book What I am doing is trying to get 3 'content' (content being a name and cause of death) divs onto 1 page, and then generate a new page. So here is what i want: <div id="deathnote"> //starts book <div style="background-image:url(images/coverpage.jpg);"></div> //creates new page <div style="background-image:url(images/paper.jpg);"></div> //creates new page <div style="background-image:url(images/paper.jpg);"> //creates new page but leaves it open <div> CONTENT </div> <div> CONTENT </div> <div> CONTENT </div> </div> //ends the page </div> //ends book Seems simple enough, however the content is data from a MySQL DB, so i have to echo it in using PHP. Here is what i have so far <div id="deathnote"> <div style="background-image:url(images/coverpage.jpg);"></div> <div style="background-image:url(images/paper.jpg);"></div> <div style="background-image:url(images/paper.jpg);"></div> <div style="background-image:url(images/paper.jpg);"></div> <div style="background-image:url(images/paper.jpg);"></div> <div style="background-image:url(images/paper.jpg);"></div> <?php $pagecount = 0; $db = new mysqli('localhost', 'username', 'passw', 'DB'); if($db->connect_errno > 0){ die('Unable to connect to database [' . $db->connect_error . ']'); } $sql = <<<SQL SELECT * FROM `TABLE` SQL; if(!$result = $db->query($sql)){ die('There was an error running the query [' . $db->error . ']'); } //IGNORE ALL OF THE GARBAGE ABOVE. IT IS SIMPLE CONNECTING SCRIPT THAT I KNOW WORKS //THE METHOD I AM HAVING TROUBLE WITH IS BELOW $pagecount = 0; while($row = $result->fetch_assoc()){ //GETS THE VALUE (and makes sure it isn't nothing echo '<div style="background-image:url(images/paper.jpg);">'; //THIS OPENS A NEW PAGE while ($pagecount !== 3) { //KEEPS COUNT OF HOW MUCH CONTENT DIVS IS ON THE PAGE while($row = $result->fetch_assoc()){ //START A CONTENT DIV echo '<div class="content"><div class="name">' . $row['victim'] . '</div><div class="cod">' . $row['cod'] . '</div></div>'; //END A CONTENT DIV $pagecount++; //UP THE PAGE COUNT } } $pagecount=0; //PUT IT BACK TO 0 echo '</div>'; //END PAGE } $db->close(); ?> <div style="background-image:url(images/backpage.jpg);"></div> //BACK PAGE </div> At the moment i seem to be causing and infinite loop so the page won't load. The problem resides within the while loops. Any help is greatly appreciated. Thanks in advance guys. :)

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  • Avoiding dog-piling or thundering herd in a memcached expiration scenario

    - by Quintin Par
    I have the result of a query that is very expensive. It is the join of several tables and a map reduce job. This is cached in memcached for 15 minutes. Once the cache expires the queries are obviously run and the cache warmed again. But at the point of expiration the thundering herd problem issue can happen. One way to fix this problem, that I do right now is to run a scheduled task that kicks in the 14th minute. But somehow this looks very sub optimal to me. Another approach I like is nginx’s proxy_cache_use_stale updating; mechanism. The webserver/machine continues to deliver stale cache while a thread kicks in the moment expiration happens and updates the cache. Has someone applied this to memcached scenario though I understand this is a client side strategy? If it benefits, I use Django.

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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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  • 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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  • 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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