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  • list or container O(1)-ish insertion/deletion performance, with array semantics

    - by Chris Kaminski
    I'm looking for a collection that offers list semantics, but also allows array semantics. Say I have a list with the following items: apple orange carrot pear then my container array would: container[0] == apple container[1] == orangle container[2] == carrot Then say I delete the orange element: container[0] == apple container[1] == carrot I don't particularly care if sort order is maintained, I'd just like the array values to function as accelerators to the list items, and I want to collapse gaps in the array without having to do an explicit resizing.

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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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  • Need sorted dictionary designed to find values with keys less or greater than search value

    - by Captain Comic
    Hi I need to have objects sorted by price (decimal) value for fast access. I need to be able to find all objects with price more then A or less than B. I was thinkg about SortedList, but it does not provide a way to find ascending or descending enumerator starting from given key value (say give me all objects with price less than $120). Think of a system that accepts items for sell from users and stores them into that collection. Another users want to find items cheaper than $120. Basically what i need is tree-based collection and functionality to find node that is smaller\greater\equal to provided key. Please advice.

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  • Is there a way to define a List<> of two elements string array?

    - by Alexander Prokofyev
    I want to build two-dimentional array of strings where length of one dimention is 2. Similar to this string[,] array = new string[,] { {"a", "b"}, {"c", "d"}, {"e", "f"}, {"g", "h"} } Doing List<string[]> list = new List<string[]>(); list.Add(new string[2] {"a", "b"}); list.Add(new string[2] {"c", "d"}); list.Add(new string[2] {"e", "f"}); list.Add(new string[2] {"g", "h"}); list.ToArray(); gives me string[][] but not string[,] array. Just curious, is there some trick to build dynamically string[,] array somehow?

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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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  • 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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  • How to store a scaleable sized extensible event log?

    - by firoso
    Hello everyone! I've been contemplating writing a simple "event log" that takes a paramater list and stores event messages in a log file, trouble is, I forsee this file growing to be rather large (assume 1M entries or more) the question is, how can I implement this system without pulling teeth, I know that SQL would be a possible way to go. XML would be ideal but not really practical for scaleability if i'm not going nuts. Example Log Entry -----Time Date-------- ---------Sender----------------------- ---------Tags---------- --Message---------- 12/24/2008 24:00:00 $DOMAIN\SYSTEM\Application$ :Trivial: :Notification: It's Christmas in 1s

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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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  • 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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  • Best datastructure for frequently queried list of objects

    - by panzerschreck
    Hello, I have a list of objects say, List. The Entity class has an equals method,on few attributes ( business rule ) to differentiate one Entity object from the other. The task that we usually carry out on this list is to remove all the duplicates something like this : List<Entity> noDuplicates = new ArrayList<Entity>(); for(Entity entity: lstEntities) { int indexOf = noDuplicates.indexOf(entity); if(indexOf >= 0 ) { noDuplicates.get(indexOf).merge(entity); } else { noDuplicates.add(entity); } } Now, the problem that I have been observing is that this part of the code, is slowing down considerably as soon as the list has objects more than 10000.I understand arraylist is doing a o(N) search. Is there a faster alternative, using HashMap is not an option, because the entity's uniqueness is built upon 4 of its attributes together, it would be tedious to put in the key itself into the map ? will sorted set help in faster querying ? Thanks

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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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  • 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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  • Why use hashing to create pathnames for large collections of files?

    - by Stephen
    Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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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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  • two HashMap iteration

    - by user431276
    I have two HashMaps and I can iterate both hashmaps with following code Iterator it = mp.entrySet().iterator(); while (it.hasNext()) { Map.Entry pairs = (Map.Entry)it.next(); String firstVal = pairs.getValue(); } Iterator it2 = mp2.entrySet().iterator(); while (it2.hasNext()) { Map.Entry pairs2 = (Map.Entry)it.next(); String SecondVal = pairs2.getValue(); } myFunction(firstVal, SecondVal) Is there anyway to iterate two hashmaps at the same time without using two loops? Currently, I have a method that accepts two parameters and each parameter value is stored in first and second hashmap. I have to iterate first hash then second to get values. I think there must be a good way to do it but I don't know :( P.S: there could be some errors in above code as this is just an example to explain my problem. Each iterator is a method in original program and accept one parameter. I couldn't copy past real time functions as they are HUGE !

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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 to optimize this Python code?

    - by RandomVector
    def maxVote(nLabels): count = {} maxList = [] maxCount = 0 for nLabel in nLabels: if nLabel in count: count[nLabel] += 1 else: count[nLabel] = 1 #Check if the count is max if count[nLabel] > maxCount: maxCount = count[nLabel] maxList = [nLabel,] elif count[nLabel]==maxCount: maxList.append(nLabel) return random.choice(maxList) nLabels contains a list of integers. The above function returns the integer with highest frequency, if more than one have same frequency then a randomly selected integer from them is returned. E.g. maxVote([1,3,4,5,5,5,3,12,11]) is 5

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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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  • 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 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 does dynamic array always double by a factor of 2?

    - by Phoenix
    I was wondering how does one decide the resizing factor by which dynamic array resizes ? On wikipedia and else where I have always seen the number of elements being increased by a factor of 2? Why 2? Why not 3? how does one decide this factor ? IF it is language dependent I would like to know this for Java.

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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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