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  • Skip Lists -- ever used them?

    - by Head Geek
    I'm wondering whether anyone here has ever used a skip list. It looks to have roughly the same advantages as a balanced binary tree, but is simpler to implement. If you have, did you write your own, or use a pre-written library (and if so, what was its name)?

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  • Huge Graph Structure

    - by Harph
    I'm developing an application in which I need a structure for represent a huge graph (between 1000000 and 6000000 nodes and 100 or 600 edges) in memory. The edges representation will contain some attribute of the relation. I have tried a memory map representation, arrays, dictionaries and string for represent that structure in memory, but this always crash because the memory limit. I would to get an advice of how can I represent this, or something similar. By the way, I'm using python.

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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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  • What's the best way of using a pair (triple, etc) of values as one value in C#?

    - by Yacoder
    That is, I'd like to have a tuple of values. The use case on my mind: Dictionary<Pair<string, int>, object> or Dictionary<Triple<string, int, int>, object> Are there built-in types like Pair or Triple? Or what's the best way of implementing it? Update There are some general-purpose tuples implementations described in the answers, but for tuples used as keys in dictionaries you should additionaly verify correct calculation of the hash code. Some more info on that in another question. Update 2 I guess it is also worth reminding, that when you use some value as a key in dictionary, it should be immutable.

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  • html5 uploader + jquery drag & drop: how to store file data with FormData?

    - by lauthiamkok
    I am making a html5 drag and drop uploader with jquery, below is my code so far, the problem is that I get an empty array without any data. Is this line incorrect to store the file data - fd.append('file', $thisfile);? $('#div').on( 'dragover', function(e) { e.preventDefault(); e.stopPropagation(); } ); $('#div').on( 'dragenter', function(e) { e.preventDefault(); e.stopPropagation(); } ); $('#div').on( 'drop', function(e){ if(e.originalEvent.dataTransfer){ if(e.originalEvent.dataTransfer.files.length) { e.preventDefault(); e.stopPropagation(); // The file list. var fileList = e.originalEvent.dataTransfer.files; //console.log(fileList); // Loop the ajax post. for (var i = 0; i < fileList.length; i++) { var $thisfile = fileList[i]; console.log($thisfile); // HTML5 form data object. var fd = new FormData(); //console.log(fd); fd.append('file', $thisfile); /* var file = {name: fileList[i].name, type: fileList[i].type, size:fileList[i].size}; $.each(file, function(key, value) { fd.append('file['+key+']', value); }) */ $.ajax({ url: "upload.php", type: "POST", data: fd, processData: false, contentType: false, success: function(response) { // .. do something }, error: function(jqXHR, textStatus, errorMessage) { console.log(errorMessage); // Optional } }); } /*UPLOAD FILES HERE*/ upload(e.originalEvent.dataTransfer.files); } } } ); function upload(files){ console.log('Upload '+files.length+' File(s).'); }; then if I use another method is that to make the file data into an array inside the jquery code, var file = {name: fileList[i].name, type: fileList[i].type, size:fileList[i].size}; $.each(file, function(key, value) { fd.append('file['+key+']', value); }); but where is the tmp_name data inside e.originalEvent.dataTransfer.files[i]? php, print_r($_POST); $uploaddir = './uploads/'; $file = $uploaddir . basename($_POST['file']['name']); if (move_uploaded_file($_POST['file']['tmp_name'], $file)) { echo "success"; } else { echo "error"; } as you can see that tmp_name is needed to upload the file via php... html, <div id="div">Drop here</div>

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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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  • [BST] Deletion procedure

    - by Metz
    Hi all. Consider the deletion procedure on a BST, when the node to delete has two children. Let's say i always replace it with the node holding the minimum key in its right subtree. The question is: is this procedure commutative? That is, deleting x and then y has the same result than deleting first y and then x? I think the answer is no, but i can't find a counterexample, nor figure out any valid reasoning. Thank you. EDIT: Maybe i've got to be clearer. Consider the transplant(node x, node y) procedure: it replace x with y (and its subtree). So, if i want to delete a node (say x) which has two children i replace it with the node holding the minimum key in its right subtree: y = minimum(x.right) transplant(y, y.right) // extracts the minimum (it doesn't have left child) y.right = x.right y.left = x.left transplant(x,y) The question was how to prove the procedure above is not commutative.

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  • How are two-dimensional arrays formatted in memory?

    - by Chris Cooper
    In C, I know I can dynamically allocate a two-dimensional array on the heap using the following code: int** someNumbers = malloc(arrayRows*sizeof(int*)); for (i = 0; i < arrayRows; i++) { someNumbers[i] = malloc(arrayColumns*sizeof(int)); } Clearly, this actually creates a one-dimensional array of pointers to a bunch of separate one-dimensional arrays of integers, and "The System" can figure you what I mean when I ask for: someNumbers[4][2]; But when I statically declare a 2D array, as in the following line...: int someNumbers[ARRAY_ROWS][ARRAY_COLUMNS]; ...does a similar structure get created on the stack, or is it of another form completely? (i.e. is it a 1D array of pointers? If not, what is it, and how do references to it get figured out?) Also, when I said, "The System," what is actually responsible for figuring that out? The kernel? Or does the C compiler sort it out while compiling?

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  • How do I output the preorder traversal of a tree given the inorder and postorder tranversal?

    - by user342580
    Given the code for outputing the postorder traversal of a tree when I have the preorder and the inorder traversal in an interger array. How do I similarily get the preorder with the inorder and postorder array given? void postorder( int preorder[], int prestart, int inorder[], int inostart, int length) { if(length==0) return; //terminating condition int i; for(i=inostart; i<inostart+length; i++) if(preorder[prestart]==inorder[i])//break when found root in inorder array break; postorder(preorder, prestart+1, inorder, inostart, i-inostart); postorder(preorder, prestart+i-inostart+1, inorder, i+1, length-i+inostart-1); cout<<preorder[prestart]<<" "; } Here is the prototype for preorder() void preorder( int inorderorder[], int inostart, int postorder[], int poststart, int length)

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  • Why increase pointer by two while finding loop in linked list, why not 3,4,5?

    - by GG
    I had a look at question already which talk about algorithm to find loop in a linked list. I have read Floyd's cycle-finding algorithm solution, mentioned at lot of places that we have to take two pointers. One pointer( slower/tortoise ) is increased by one and other pointer( faster/hare ) is increased by 2. When they are equal we find the loop and if faster pointer reaches null there is no loop in the linked list. Now my question is why we increase faster pointer by 2. Why not something else? Increasing by 2 is necessary or we can increase it by X to get the result. Is it necessary that we will find a loop if we increment faster pointer by 2 or there can be the case where we need to increment by 3 or 5 or x.

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  • How to find longest common substring using trees?

    - by user384706
    The longest common substring problem according to wiki can be solved using a suffix tree. From wiki: The longest common substrings of a set of strings can be found by building a generalised suffix tree for the strings, and then finding the deepest internal nodes which have leaf nodes from all the strings in the subtree below it I don't get this. Example: if I have: ABCDE and XABCZ then the suffix tree is (some branches from XABCZ omitted due to space): The longest common substring is ABC but it is not I can not see how the description of wiki helps here. ABC is not the deepest internal nodes with leaf nodes. Any help to understand how this works?

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  • about Sorting Algorithms

    - by matin1234
    Hi I want to know that we always use Sorting algorithm like (Insertion Sort or Merge Sort,...) just for lists and arrays?? and we do not use these algorithms for stack or queue ??? thanks

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  • Is there a module that implements an efficient array type in Erlang?

    - by dsmith
    I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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  • algorithm - How to sort a 0/1 array with 2n/3 comparisons?

    - by Jackson Tale
    In Algorithm Design Manual, there is such an excise 4-26 Consider the problem of sorting a sequence of n 0’s and 1’s using comparisons. For each comparison of two values x and y, the algorithm learns which of x < y, x = y, or x y holds. (a) Give an algorithm to sort in n - 1 comparisons in the worst case. Show that your algorithm is optimal. (b) Give an algorithm to sort in 2n/3 comparisons in the average case (assuming each of the n inputs is 0 or 1 with equal probability). Show that your algorithm is optimal. For (a), I think it is fairly easy. I can choose a[n-1] as pivot, then do something like in quicksort partition, scan 0 to n - 2, find the middle point where left side is all 0 and right side is all 1, this take n - 1 comparisons. But for (b), I can't get a clue. It says "each of the n inputs is 0 or 1 with equal probability", so I guess I can assume the numbers of 0 and 1 equal? But how can I get a result which is related to 1/3? divide the whole array into 3 groups? Thanks

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  • Is there any reason why someone would want to create an Core Data model programmatically?

    - by mystify
    I wonder in which cases it would be good to make an NSManagedObjectModel completely programmatically, with NSEntityDescription instances and all this stuff. I'm that kind of person who prefers to code programmatically, rejecting Interface Builder. But when it comes to Core Data, I have a hard time figuring out why I should kill my time NOT using the nice Xcode Data Modeler tool. And since data models are stuck to a given state (except when you want to do some ugly migration operations where thinks probably go wrong and users get mad, really mad), I see no big sense in a data model that's made programmatically for the purpose of changing it all the time. Did I miss something?

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  • How do I remove the leaves of a binary tree?

    - by flopex
    I'm trying to remove all of the leaves. I know that leaves have no children, this is what I have so far. public void removeLeaves(BinaryTree n){ if (n.left == null && n.right == null){ n = null; } if (n.left != null) removeLeaves(n.left); if (n.right != null) removeLeaves(n.right); }

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  • In-order tree traversal

    - by Chris S
    I have the following text from an academic course I took a while ago about in-order traversal (they also call it pancaking) of a binary tree (not BST): In-order tree traversal Draw a line around the outside of the tree. Start to the left of the root, and go around the outside of the tree, to end up to the right of the root. Stay as close to the tree as possible, but do not cross the tree. (Think of the tree — its branches and nodes — as a solid barrier.) The order of the nodes is the order in which this line passes underneath them. If you are unsure as to when you go “underneath” a node, remember that a node “to the left” always comes first. Here's the example used (slightly different tree from below) However when I do a search on google, I get a conflicting definition. For example the wikipedia example: Inorder traversal sequence: A, B, C, D, E, F, G, H, I (leftchild,rootnode,right node) But according to (my understanding of) definition #1, this should be A, B, D, C, E, F, G, I, H Can anyone clarify which definition is correct? They might be both describing different traversal methods, but happen to be using the same name. I'm having trouble believing the peer-reviewed academic text is wrong, but can't be certain.

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  • MySQL Cluster data nodes - slow SELECTs

    - by Boyan Georgiev
    Hi to all. First off, I'm new to MySQL Cluster. This is my pain: I've managed to setup a MySQL Cluster with two data nodes, two SQL nodes and one management server. Everything works pretty well, except the following: my data nodes are spread across an intranet link which incurs latency into communications between the data nodes. Apparently, due to MySQL Cluster's internal partitioning schemes, when my PHP application pulls data from the cluster via SELECT queries, parts of the data are pulled from both data nodes. This makes the page appear onscreen REALLY slowly. If I bring one data node offline, the data can only be pulled from that single remaining data node, and thus, the final result (HTML output) appears on the screen in a very timely fashion. So, my question is this: can the data nodes/cluster be told to pull data from partitions stored only on a particular data node?

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  • How to structure a Visual Studio project for the data access layer

    - by Akk
    I currently have a project that uses various DB access technologies mainly for showcasing or for demos. Currently we have: Namespace App.Data (App.Data.dll) Folder NHibernate Folder EntityFramework Folder LinqToSql The above structure is ok as we only use Sql Server as the DB. But going forward we will be including Oracle, MySql etc. So what would be a better structure with this in mind? I thought about: Namespace App.Data.SqlServer (App.Data.SqlServer.dll) Folder NHibernate Folder EntityFramework Folder LinqToSql Or would it just be better to have separate assemblies for each database and access technology?: Namespace App.Data.SqlServer.NHibernate (App.Data.SqlServer.NHibernate.dll) Namespace App.Data.SqlServer.EntityFramework(App.Data.SqlServer.EntityFramework.dll) Namespace App.Data.Oracle.NHibernate (App.Data.Oracle.NHibernate.dll) Namespace App.Data.MySql.NHibernate (App.Data.MySql.Oracle.dll)

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  • Fast exchange of data between unmanaged code and managed code

    - by vizcaynot
    Hello: Without using p/invoke, from a C++/CLI I have succeeded in integrating various methods of a DLL library from a third party built in C. One of these methods retrieves information from a database and stores it in different structures. The C++/CLI program I wrote reads those structures and stores them in a List<, which is then returned to the corresponding reading and use of an application programmed completely in C#. I understand that the double handling of data (first, filling in several structures and then, filling all of these structures into a list<) may generate an unnecessary overload, at which point I wish C++/CLI had the keyword "yield". Depending on the above scenario, do you have recommendations to avoid or reduce this overload? Thanks.

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  • Time Complexities of recursive algorithms

    - by Peter
    Whenever I see a recursive solution, or I write recursive code for a problem, it is really difficult for me to figure out the time complexity, in most of the cases I just say its exponential? How is it exponential actually? How people say it is 2^n, when it is n!, when it is n^n or n^k. I have some questions in mind, let say find all permutations of a string (O(n!)) find all sequences which sum up to k in an array (exponential, how exactly do I calculate). Find all subsets of size k whose sum is 0 (will k come somewhere in complexity , it should come right?). Can any1 help me how to calculate the exact complexity of such questions, I am able to wrote code for them , but its hard understanding the exact time complexity.

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  • When does it make sense to use a map?

    - by kiwicptn
    I am trying to round up cases when it makes sense to use a map (set of key-value entries). So far I have two categories (see below). Assuming more exist, what are they? Please limit each answer to one unique category and put up an example. Property values (like a bean) age -> 30 sex -> male loc -> calgary Presence, with O(1) performance peter -> 1 john -> 1 paul -> 1

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