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  • K-nearest neighbour with closed-loop dimensions

    - by Tomas
    Hi, I've got a K-nearest neighbour problem where some of the dimensions are closed loops. For example one is 'time of day' and I'm matching for similarity so 'very early morning' is close to 'late evening', you can't just make it a linear scale from 'very early morning' at one end to 'late evening' at the other. How can I represent this in the data model? Is there an established way to handle this or a way to work around it?

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  • How can I declare a pointer structure?

    - by Y_Y
    This probably is one of the easiest questions ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head?

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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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  • Reading a C/C++ data structure in C# from a byte array

    - by Chris Miller
    What would be the best way to fill a C# struct from a byte[] array where the data was from a C/C++ struct? The C struct would look something like this (my C is very rusty): typedef OldStuff { CHAR Name[8]; UInt32 User; CHAR Location[8]; UInt32 TimeStamp; UInt32 Sequence; CHAR Tracking[16]; CHAR Filler[12];} And would fill something like this: [StructLayout(LayoutKind.Explicit, Size = 56, Pack = 1)]public struct NewStuff{ [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)] [FieldOffset(0)] public string Name; [MarshalAs(UnmanagedType.U4)] [FieldOffset(8)] public uint User; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)] [FieldOffset(12)] public string Location; [MarshalAs(UnmanagedType.U4)] [FieldOffset(20)] public uint TimeStamp; [MarshalAs(UnmanagedType.U4)] [FieldOffset(24)] public uint Sequence; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)] [FieldOffset(28)] public string Tracking;} What is best way to copy OldStuff to NewStuff, if OldStuff was passed as byte[] array? I'm currently doing something like the following, but it feels kind of clunky. GCHandle handle;NewStuff MyStuff;int BufferSize = Marshal.SizeOf(typeof(NewStuff));byte[] buff = new byte[BufferSize];Array.Copy(SomeByteArray, 0, buff, 0, BufferSize);handle = GCHandle.Alloc(buff, GCHandleType.Pinned);MyStuff = (NewStuff)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(NewStuff));handle.Free(); Is there better way to accomplish this?

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  • Java data structure suggestion.

    - by techoverflow
    Hi folks, I am a newbie in this field so please excuse my silly mistakes :) So the issue I am facing is: On my webpage, I am displaying a table. For now my issue is concerned with three columns of the table. First is : Area Code Second is : Zone Code Third is: Value The relationship between these three is: 1 Area Code has 6 different Zone code's and all those 6 Zone codes have corresponding "Value" I need a data structer that would give me the flexibility to get a "Value" for a Zone code, which falls under a particular Area code. I have the same zone codes for all the Area codes: Zone codes are: 111, 222, 333, 444, 555, 666 After surfing your stackoverflow, I thought I can go with this structure: Map<Integer, Map<Integer, Double>> retailPrices = new HashMap<Integer, Map<Integer, Double>>(); Map<Integer, Double> codes = new HashMap<Integer, Double>(); where reatailPrices would hold an Area Code and a Map of Zone code as Key and "Value" as Value. but when I am trying to populate this through a SQL resultset, I am getting the following error: The method put(Integer, Map<Integer,Double>) in the type Map is not applicable for the arguments (Integer, Double) on line: `while(oResult.next()) retailPrices.put((new Integer(oResult.getString("AREA"))), (pegPlPrices.put(new Integer(oResult.getString("ZONE_CODE")), new Double(oResult.getString("VALUE"))))); }` please help me figure out this problem. Am I following the right approach?

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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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  • Good ways to map a 2D side shooter (somewhat like liero, or soldat)

    - by Blaze
    I'm wondering what way would be best to render a 2D map for a shooter (these will be static maps) similar to Soldat. Multiple options I've considered are a tile based map (stored in txt files), or just creating different classes for the different terrains I plan to use and creating a data structure to read/store them in a file. (I want to also be able to include things like jumping/running on walls, sliding down walls/slopes ect) I feel like there must be a better way than either of these, but haven't been able to find definitive information :/ Thanks :)

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  • Chess board position numbers in 6-rooted-binary tree?

    - by HH
    The maximum number of adjacent vertices is 6 that corresponds to the number of roots. By the term root, I mean the number of children for each node. If adjacent square is empty, fill it with Z-node. So every square will have 6 nodes. How can you formulate it with binary tree? Is the structure just 6-rooted-binary tree? What is the structure called if nodes change their positions? Suppose partially ordered list where its units store a large randomly expanding board. I want a self-adjusting data structure, where it is easy to calculate distances between nodes. What is its name?

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  • basic json > struct question

    - by danwoods
    I'm working with twitter's api, trying to get the json data from http://search.twitter.com/trends/current.json which looks like: {"as_of":1268069036,"trends":{"2010-03-08 17:23:56":[{"name":"Happy Women's Day","query":"\"Happy Women's Day\" OR \"Women's Day\""},{"name":"#MusicMonday","query":"#MusicMonday"},{"name":"#MM","query":"#MM"},{"name":"Oscars","query":"Oscars OR #oscars"},{"name":"#nooffense","query":"#nooffense"},{"name":"Hurt Locker","query":"\"Hurt Locker\""},{"name":"Justin Bieber","query":"\"Justin Bieber\""},{"name":"Cmon","query":"Cmon"},{"name":"My World 2","query":"\"My World 2\""},{"name":"Sandra Bullock","query":"\"Sandra Bullock\""}]}} My structs look like: type trend struct { name string query string } type trends struct { id string arr_of_trends []trend } type Trending struct { as_of string trends_obj trends } and then I parse the JSON into a variable of type Trending. I'm very new to JSON so my main concern is making sure I've have the data structure correctly setup to hold the returned json data. I'm writing this in 'Go' for a project for school. (This is not part of a particular assignment, just something I'm demo-ing for a presentation on the language)

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  • Result of Long Positive Integers & Search and element in array..

    - by AGeek
    Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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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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  • 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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  • 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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  • Better data-structure design

    - by Tempname
    Currently in my application I have a single table that is giving me a bit of trouble. The issue at hand is I have a value object that is mapped to this table. When the data is returned to me as an array of value objects, I have to then loop through this array and begin my recursion by matching the ParentID to parent ObjectID's. The column ParentID is either null (acts a parent) or it holds the value of an ObjectID. I know there has to be a better way to create this data structure so that I do not have to do recursive loops to match ParentID's with their ObjectID's. Any help with this is greatly appreciated. Here is the table in describe form: +----------------+------------------+------+-----+---------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------+------------------+------+-----+---------------------+-----------------------------+ | ObjectID | int(11) unsigned | NO | PRI | NULL | auto_increment | | ObjectHeight | decimal(6,2) | NO | | NULL | | | ObjectWidth | decimal(6,2) | NO | | NULL | | | ObjectX | decimal(6,2) | NO | | NULL | | | ObjectY | decimal(6,2) | NO | | NULL | | | ObjectLabel | varchar(255) | NO | | NULL | | | TemplateID | int(11) unsigned | NO | MUL | NULL | | | ObjectTypeID | int(11) unsigned | NO | MUL | NULL | | | ParentID | int(11) unsigned | YES | MUL | NULL | | | CreationDate | datetime | YES | | 0000-00-00 00:00:00 | | | LastModifyDate | timestamp | YES | | NULL | on update CURRENT_TIMESTAMP | +----------------+------------------+------+-----+---------------------+-----------------------------+e

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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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  • python dictionary with constant value-type

    - by s.kap
    hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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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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  • Multidimensional data structure?

    - by Austin Truong
    I need a multidimensional data structure with a row and a column. Must be able to insert elements any location in the data structure. Example: {A , B} I want to insert C in between A and B. {A, C, B}. Dynamic: I do not know the size of the data structure. Another example: I know the [row][col] of where I want to insert the element. EX. insert("A", 1, 5), where A is the element to be inserted, 1 is the row, 5 is the column. EDIT I want to be able to insert like this. static void Main(string[] args) { Program p = new Program(); List<string> list = new List<string>(); list.Insert(1, "HELLO"); list.Insert(5, "RAWR"); for (int i = 0; i < list.Count; i++) { Console.WriteLine(list[i]); } Console.ReadKey(); } And of course this crashes with an out of bounds error. So in a sense I will have a user who will choose which ROW and COL to insert the element to.

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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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  • Item in multiple lists

    - by Evan Teran
    So I have some legacy code which I would love to use more modern techniques. But I fear that given the way that things are designed, it is a non-option. The core issue is that often a node is in more than one list at a time. Something like this: struct T { T *next_1; T *prev_1; T *next_2; T *prev_2; int value; }; this allows the core have a single object of type T be allocated and inserted into 2 doubly linked lists, nice and efficient. Obviously I could just have 2 std::list<T*>'s and just insert the object into both...but there is one thing which would be way less efficient...removal. Often the code needs to "destroy" an object of type T and this includes removing the element from all lists. This is nice because given a T* the code can remove that object from all lists it exists in. With something like a std::list I would need to search for the object to get an iterator, then remove that (I can't just pass around an iterator because it is in several lists). Is there a nice c++-ish solution to this, or is the manually rolled way the best way? I have a feeling the manually rolled way is the answer, but I figured I'd ask.

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  • implementation of a queue using a circular array

    - by matin1234
    Hi I have found these algorithms in the internet but I can not understand that why in the enqueue method we compare size with N-1??? please help me thanks!! Algorithm size(): return (N-f+r)mod N Algorithm enqueue(e): if size()=N-1 then throw a FullQueueException Q[r]<---e r<----(r+1)mod N

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