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  • Meaning of NEXT in Linked List creation in perl

    - by seleniumnewbie
    So I am trying to learn Linked Lists using Perl. I am reading "Mastering Algorithms with Perl" by Job Orwant. In the book he explains how to create a linked list I understand most of it, but I just simply fail to understand the command/index/key NEXT in the second last line of the code snippet. $list=undef; $tail=\$list; foreach (1..5){ my $node = [undef, $_ * $_]; $$tail = $node; $tail = \${$node->[NEXT]}; # The NEXT on this line? } What is he trying to do there? Isn $node a scalar, which stores the address of the unnamed array. Also even if we are de-referencing $node, should we not refer to the individual elements by an index number example (0,1). If we do use "NEXT" as a key, is $node a reference to a hash? I am very confused. Something in plain English will be highly appreciated.

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  • Java How to find a value in a linked list iteratively and recursively

    - by Roxy
    Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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  • How to implement a Linked List in Java?

    - by nbarraille
    Hello! I am trying to implement a simple HashTable in Java that uses a Linked List for collision resolution, which is pretty easy to do in C, but I don't know how to do it in Java, as you can't use pointers... First, I know that those structures are already implemented in Java, I'm not planning on using it, just training here... So I created an element, which is a string and a pointer to the next Element: public class Element{ private String s; private Element next; public Element(String s){ this.s = s; this.next = null; } public void setNext(Element e){ this.next = e; } public String getString(){ return this.s; } public Element getNext(){ return this.next; } @Override public String toString() { return "[" + s + "] => "; } } Of course, my HashTable has an array of Element to stock the data: public class CustomHashTable { private Element[] data; Here is my problem: For example I want to implement a method that adds an element AT THE END of the linked List (I know it would have been simpler and more efficient to insert the element at the beginning of the list, but again, this is only for training purposes). How do I do that without pointer? Here is my code (which could work if e was a pointer...): public void add(String s){ int index = hash(s) % data.length; System.out.println("Adding at index: " + index); Element e = this.data[index]; while(e != null){ e = e.getNext(); } e = new Element(s); } Thanks!

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  • Having trouble deleting a node from a linked list

    - by Requiem
    I've been working on this code for my shell that I'm creating and for some reason it isn't working. I'm implementing a watchuser function that watch's a user when an argument is given (args[1]). However, when a second argument (args[2]) of "off" is given, the user should be deleted from the linked list and should no longer be watched. struct userList * goList; goList = userInventory; do{ if (strcmp(userInventory->username, args[1]) == 0){ printf("%s\n", args[1]); printf("%s\n",userInventory->username); struct userList * temp2; temp2 = userInventory->next; if (userInventory->next != NULL){ userInventory->next = temp2->next; userInventory->next->prev = userInventory; } free(temp2); } goList = goList->next; }while (goList != userInventory); My global struct is also as follows: struct userList{ char * username; struct userList * prev; struct userList * next; } For reason, this code won't delete the user node from my linked list. The adding works, but this remove function won't and I'm not sure why. The print statements are there just to make sure it's executing the condition, which it is. If anyone could help me find the reasoning behind my error, I'd greatly appreciate it. Till then, I'll be trying to debug this. Thanks.

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  • Handwritten linked list is segfaulting and I don't understand why

    - by Born2Smile
    Hi I was working on a bit of fun, making an interface to run gnuplot from within c++, and for some reason the my linked list implementation fails. The code below fails on the line plots-append(&plot). Stepping through the code I discovered that for some reason the destructor ~John() is called immediately after the constructor John(), and I cannot seem to figure out why. The code included below is a stripped down version operating only on Plot*. Originally I made the linked list as a template class. And it worked fine as ll<int and ll<char* but for some reason it fails as ll<Plot*. Could youp please help me figure out why it fails? and perhaps help me understand how to make it work? In advance: Thanks a heap! //B2S #include <string.h class Plot{ char title[80]; public: Plot(){ } }; class Link{ Plot* element; Link* next; Link* prev; friend class ll; }; class ll{ Link* head; Link* tail; public: ll(){ head = tail = new Link(); head-prev = tail-prev = head-next = tail-next = head; } ~ll(){ while (head!=tail){ tail = tail-prev; delete tail-next; } delete head; } void append(Plot* element){ tail-element = element; tail-next = new Link(); tail-next-prev = tail; tail-next = tail; } }; class John{ ll* plots; public: John(){ plots= new ll(); } ~John(){ delete plots; } John(Plot* plot){ John(); plots-append(plot); } }; int main(){ Plot p; John k(&p); }

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  • Using triggers to update linked server table

    - by tabouakl
    Can I use triggers to insert or update tables in a linked server? I tried it and got the following error: Unable to start a nested transaction for OLE DB provider 'SQLOLEDB'. A nested transaction was required because the XACT_ABORT option was set to OFF. [OLE/DB provider returned message: Cannot start more transactions on this session.] OLE DB error trace [OLE/DB Provider 'SQLOLEDB' ITransactionLocal::StartTransaction returned 0x8004d013: ISOLEVEL=4096].

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  • C++ classes & linked list: adding & counting items

    - by user342289
    I need to make a linked list with classes. Each list will store two values: a URI and IP. After doing all the adding, I need to be able count the total number of items in the linked list. I have tried the following code but it doesn't compile. Any suggestions please? #include <iostream> #include <cstdlib> #include <string> using namespace std; class ip_uri_store { protected: string ip; string uri; ip_uri_store *next; public: ip_uri_store(string huri, string hip); void additem(string auri, string aip); void deleteitem(string duri); void findbyuri(string furi); void findbyip(string fip); int totalitems(); }; ip_uri_store *head = NULL; ip_uri_store *curr = NULL; void ip_uri_store::additem(string auri, string aip) { curr = head; while (curr->next != NULL) { curr = curr->next; } curr->uri = auri; curr->next = new ip_uri_store; curr->ip = aip; curr->next = new ip_uri_store; curr = curr->next; curr = head; } int ip_uri_store::totalitems() { int i = 0; curr = head; while (curr->next != NULL) { i += 1; curr = curr->next; } return i; } int main(int argc, char *argv[]) { if (argc == 1) { cout << "123456, [email protected], Gordon Brown" << endl; return (0); } head = new ip_uri_store; curr = head; int i; for (i = 1; i < argc; i++) { if (argv[i][0] == 'A') //add item { ip_uri_store.additem(argv[i + 1], argv[i + 2]); i += 2; } else if (argv[i][0] == 'N') //print total tiems { cout << ip_uri_store.totalitems() << endl; } else { cout << "command error\n"; return 0; } } return (0); }

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  • Declaring an array of linked list in C#

    - by xarzu
    I got the compile error message "Array size cannot be specified in a variable declaration (try initializing with a 'new' expression)" when I tried to declare an array of linked lists. public LinkedList[2] ExistingXMLList; Also, if I wanted to create a small array of strings, isn't this the way: string [2] inputdata;

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  • linked list elements gone?

    - by Hristo
    I create a linked list dynamically and initialize the first node in main(), and I add to the list every time I spawn a worker process. Before the worker process exits, I print the list. Also, I print the list inside my sigchld signal handler. in main(): head = NULL; tail = NULL; // linked list to keep track of worker process dll_node_t *node; node = (dll_node_t *) malloc(sizeof(dll_node_t)); // initialize list, allocate memory append_node(node); node->pid = mainPID; // the first node is the MAIN process node->type = MAIN; in a fork()'d process: // add to list dll_node_t *node; node = (dll_node_t *) malloc(sizeof(dll_node_t)); append_node(node); node->pid = mmapFileWorkerStats->childPID; node->workerFileName = mmapFileWorkerStats->workerFileName; node->type = WORK; functions: void append_node(dll_node_t *nodeToAppend) { /* * append param node to end of list */ // if the list is empty if (head == NULL) { // create the first/head node head = nodeToAppend; nodeToAppend->prev = NULL; } else { tail->next = nodeToAppend; nodeToAppend->prev = tail; } // fix the tail to point to the new node tail = nodeToAppend; nodeToAppend->next = NULL; } finally... the signal handler: void chld_signalHandler() { dll_node_t *temp1 = head; while (temp1 != NULL) { printf("2. node's pid: %d\n", temp1->pid); temp1 = temp1->next; } int termChildPID = waitpid(-1, NULL, WNOHANG); dll_node_t *temp = head; while (temp != NULL) { if (temp->pid == termChildPID) { printf("found process: %d\n", temp->pid); } temp = temp->next; } return; } Is it true that upon the worker process exiting, the SIGCHLD signal handler is triggered? If so, that would mean that after I print the tree before exiting, the next thing I do is in the signal handler which is print the tree... which would mean i would print the tree twice? But the tree isn't the same. The node I add in the worker process doesn't exist when I print in the signal handler or at the very end of main(). Any idea why? Thanks, Hristo

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  • sorting a doubly linked list with merge sort.

    - by user329820
    Hi I have found this code in the internet and it was for arrays ,I want to change it for doubly linked list(instead of index we should use pointer) would you please help me that how can i change merge method(I have changed sort method by myself) also this is not my home work ,I love working with linked list!! public class MergeSort { private DoublyLinkedList LocalDoublyLinkedList; public MergeSort(DoublyLinkedList list) { LocalDoublyLinkedList = list; } public void sort() { if (LocalDoublyLinkedList.size() <= 1) { return; } DoublyLinkedList listOne = new DoublyLinkedList(); DoublyLinkedList listTwo = new DoublyLinkedList(); for (int x = 0; x < (LocalDoublyLinkedList.size() / 2); x++) { listOne.add(x, LocalDoublyLinkedList.getValue(x)); } for (int x = (LocalDoublyLinkedList.size() / 2) + 1; x < LocalDoublyLinkedList.size`(); x++) {` listTwo.add(x, LocalDoublyLinkedList.getValue(x)); } //Split the DoublyLinkedList again MergeSort sort1 = new MergeSort(listOne); MergeSort sort2 = new MergeSort(listTwo); sort1.sort(); sort2.sort(); merge(listOne, listTwo); } private void merge(DoublyLinkedList a, DoublyLinkedList b) { int x = 0; int y = 0; int z = 0; while (x < first.length && y < second.length) { if (first[x] < second[y]) { a[z] = first[x]; x++; } else { a[z] = second[y]; y++; } z++; } //copy remaining elements to the tail of a[]; for (int i = x; i < first.length; i++) { a[z] = first[i]; z++; } for (int i = y; i < second.length; i++) { a[z] = second[i]; z++; } } }

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  • Generic linked list in c++

    - by itsaboy
    I have been struggling for too long a time now with a rather simple question about how to create a generic linked list in c++. The list should be able contain several types of structs, but each list will only contain one type of struct. The problem arises when I want to implement the getNode() function [see below], because then I have to specify which of the structs it should return. I have tried to substitute the structs with classes, where the getNode function returns a base class that is inherited by all the other classes, but it still does not do the trick, since the compiler does not allow the getNode function to return anything but the base class then. So here is some code snippet: typedef struct struct1 { int param1; (...) } struct1; typedef struct struct2 { double param1; (...) } struct2; typedef struct node { struct1 data; node* link; } node; class LinkedList { public: node *first; int nbrOfNodes; LinkedList(); void addNode(struct1); struct1 getNode(); bool isEmpty(); }; LinkedList::LinkedList() { first = NULL; nbrOfNodes = 0; } void LinkedList::addNode(struct1 newData) { if (nbrOfNodes == 0) { first = new node; first->data = newData; } else { node *it = first; for (int i = 0; i < nbrOfNodes; i++) { it = it->link; } node *newNode = new node; newNode->data = newData; it->link = newNode; } nbrOfNodes++; } bool LinkedList::isEmpty() { return !nbrOfNodes; } struct1 LinkedList::getNode() { param1 returnData = first->data; node* deleteNode = first; nbrOfNodes--; if (nbrOfNodes) first = deleteNode->link; delete deleteNode; return returnData; } So the question, put in one sentence, is as follows: How do I adjust the above linked list class so that it can also be used for struct2, without having to create a new almost identical list class for struct2 objects? As I said above, each instance of LinkedList will only deal with either struct1 or struct2. Grateful for hints or help

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  • reverse a linked list?

    - by sil3nt
    Hi there, Im trying to reverse the order of the following linked list, I've done so, But the reversed list does not seem to print out. Where have I gone wrong? //reverse the linked list #include <iostream> using namespace std; struct node{ int number; node *next; }; node *A; void addNode(node *&listpointer, int num){ node *temp; temp = new node; temp->number = num; temp->next = listpointer; listpointer = temp; } void reverseNode(node *&listpointer){ node *temp,*current; current = listpointer; temp = new node; while (true){ if (current == NULL){ temp = NULL; break; } temp->number = current->number; current = current->next; temp = temp->next; } listpointer = temp; } int main(){ A = NULL; addNode(A,1); addNode(A,2); addNode(A,3); while (true){ if (A == NULL){break;} cout<< A->number << endl; A = A->next; } cout<< "****" << endl; reverseNode(A); while (true){ if (A == NULL){break;} cout<< A->number << endl; A = A->next; } cout<< "****"<< endl; return 0; }

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  • C++ stl collections or linked lists

    - by Lucas
    I'm developing a OpenGL based simulation in C++. I'm optmizing my code now and i see throughout the code the frequently use of std:list and std:vector. What is the more performatic: to continue using C++ stl data structs or a pointer based linked list? The main operation that involve std::list and std::vector is open a iterator and loop through all items in the data structs and apply some processing

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  • Programmatically creating linked tables in access

    - by newtoaccess
    Hi all, We need to find a way to programatically *link all the tables* in a SQL Server database to an access db. We will be invoking this access database from a program that uses .net/SQL Server 2008. While invoking the application we would like to add the linked tables so that the users can just run the reports/modules from access without having to worry about linking the tables. Is there a way we can do this? Thanks!

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  • linked-list interview question

    - by giri
    Hi This was the question asked in interview.Can anybody help me out it in implementing in java Given 2 linked lists(which need not have unique elements) find intersection point in the form of Y.(it can be anywhere--middle or tail)

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  • Display problem after deletion in linked list in C

    - by LuckySlevin
    Hi, actually this was another problem but it changed so I decided to open a new question. My code is typedef struct inner_list { int count; char word[100]; inner_list*next; } inner_list; typedef struct outer_list { char word [100]; inner_list * head; int count; outer_list * next; } outer_list; void delnode(outer_list **head,char num[100])//thanks to both Nir Levy and Jeremy P. { outer_list *temp, *m; m=temp=*head; /*FIX #1*/ while(temp!=NULL) { if(strcmp(temp->word,num)==0) { if(temp==*head) { delinner(temp->head); /* FIX#2 */ *head=temp->next; free(temp); return; } else { delinner(temp->head); /* FIX#2 */ m->next=temp->next; free(temp); return; } } else { m=temp; temp= temp->next; } } printf(" ELEMENT %s NOT FOUND ", num); } void delinner(inner_list *head) { /* FIX#2 */ inner_list *temp; temp=head; while(temp!=NULL) { head=temp->next; free(temp); temp=head; } } void delnode2(outer_list *up,inner_list **head,char num[100]) { inner_list *temp2,*temp, *m; outer_list *p; p = up; while(p!=NULL){m=temp=temp2=p->head; while(temp!=NULL) { if(strcmp(temp->word,num)==0) { if(temp==(*head)) { *head=temp->next; free(temp); return; } else { m->next=temp->next; free(temp); return; } } else { m=temp; temp= temp->next; } } p=p->next; } printf(" ELEMENT %s NOT FOUND ", num); } void print_node(outer_list *parent_node) { while(parent_node!=NULL){ printf("%s\t%d\t", parent_node->word, parent_node->count); inner_list *child_node = parent_node->head; printf("list: "); if(child_node ==NULL){printf("BUARADA");} while (child_node != NULL) { printf("%s-%d", child_node->word,child_node->count); child_node = child_node->next; if (child_node != NULL) { printf("->"); } } printf("\n"); parent_node = parent_node->next; } } While deleting an element from outer list I am also trying the delete the same element from inner_list too. For example: - Let's say aaa is an element of outer_list linked list and let's point it with outer_list *p - This aaa can also be in an inner_list linked list too. (it can be in p-head or another innerlist.) Now, the tricky part again. I tried to apply the same rules with outer_list deletion but whenever i delete the head element of inner_list it gives an error. Where is the wrong thing in print_node or delnode2?

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  • Counting number of times an item occurs in a linked list

    - by HanaCHaN92
    Here is the assignment: Here's the assignment: Implement a method countValue() that counts the number of times an item occurs in a linked list. Remember to use the STL list. int countValue(list front, const int item); Generate 20 random numbers in the range of 0 to 4, and insert each number in the linked list. Output the list by using a method which you would call writeLinkedList which you would add to the ListP.cpp. In a loop, call the method countValue() , and display the number of occurrences of each value from 0 to 4 in the list. Remember that all the above is to be included in the file ListP.ccp Run: 2 3 4 0 1 0 2 4 2 3 3 4 3 3 3 0 0 2 0 2 0 : 5, 1 : 1, 2 : 5, 3 : 6, 4 : 3 and here is what I have so far: #include<iostream> #include<list> #include<tchar.h> int countValue(list<int> front, const int item); using namespace std; int _tmain(int argc, _TCHAR* argv[]){ list<int> front; int listCount; cout << "Enter the size of the list: "; cin >> listCount; for (int i = 1; i <= listCount; i++) front.insert(rand()%5); cout << "Original List of Values: " << endl; //writeLinkedList(front, " "); cout << endl; for(int j=0;j<5;++j) cout << countValue (front,j) << endl; cout << endl; return 0; } int countValue(list<int> front, const int item) { int count0; int count1; int count2; int count3; int count4; list<int> *List; for(list<int>::iterator i = front.begin(); i != front.end(); i++) { if(List->item == 0) { count0++; } if(List->item == 1) { count1++; } if(List->item == 2) { count2++; } if(List->item == 3) { count2++; }if(List->item == 4) { count4++; } } } And here are the errors: error C2065: 'list' : undeclared identifier line 5 error C2062: type 'int' unexpected line 5 error C2661: 'std::list<_Ty>::insert' : no overloaded function takes 1 arguments line 16 error C3861: 'countValue': identifier not found line 21 IntelliSense: no instance of overloaded function "std::list<_Ty, _Ax>::insert [with _Ty=int, _Ax=std::allocator<int>]" matches the argument list line 16 IntelliSense: too few arguments in function call line 16 error C2039: 'item': is not a member of 'std::list<_Ty>' lines 34, 38, 42, 46, 49 IntelliSense: declaration is incompatible with "int countValue" (declared at line 5) line 25 IntelliSense: class "std::list<int, std:: allocator<int>>" has no member "item" lines 34, 38, 42, 46, 49 I just want to know what I've done wrong and how to fix it and also if someone could help me figure out if I'm doing the countValue function wrong or not based on the instructions I would really appreciate it. I've read the chapter in our textbook several times, looked up tutorials on youtube and on Dream in Code, and still I can not figure this out. All helpful information is appreciated!

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  • Algorithm to create a linked list from a set of nodes

    - by user320587
    Hi, I am looking for an algorithm to create a linked list from a set of nodes. For example, let's assume a node is an airline ticket from a source point to destination. (e.g., Chicago to Detroit) and there are several airline tickets. Assuming all these airline tickets are jumbled, what is the best way to determine the entire journey path. If there are 5 airline tickets like Chicago-Detroit, Denver-Chicago, Detroit-DC, DC-New York, San Jose-Denver, the algorithm should be able to come up with the correct start to end path. San Jose - Denver - Chicago - Detroit - DC - New York

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  • Search algorithm for a sorted double linked list

    - by SalamiArmi
    As a learning excercise, I've just had an attempt at implementing my own 'merge sort' algorithm. I did this on an std::list, which apparently already had the functions sort() and merge() built in. However, I'm planning on moving this over to a linked list of my own making, so the implementation is not particuarly important. The problem lies with the fact that a std::list doesnt have facilities for accessing random nodes, only accessing the front/back and stepping through. I was originally planning on somehow performing a simple binary search through this list, and finding my answer in a few steps. The fact that there are already built in functions in an std::list for performing these kinds of ordering leads me to believe that there is an equally easy way to access the list in the way I want. Anyway, thanks for your help in advance!

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  • n elements in singly linked list

    - by Codenotguru
    The following function is trying to find the nth to last element of a singly linked list. for ex: if the elements are 8-10-5-7-2-1-5-4-10-10 then the result is 7th to last node is 7. Can anybody help me on how this code is working or is there a better and simpler approach? LinkedListNode nthToLast(LinkedListNode head, int n) { if (head == null || n < 1) { return null; } LinkedListNode p1 = head; LinkedListNode p2 = head; for (int j = 0; j < n - 1; ++j) { // skip n-1 steps ahead if (p2 == null) { return null; // not found since list size < n } p2 = p2.next; } while (p2.next != null) { p1 = p1.next; p2 = p2.next; } return p1; }

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  • Problems with Linked List in C

    - by seePhor
    Hey everyone, I am new to C and I am working on an XOR linked list for a project. I have most of the code done, but I can't seem to get the delete function of the list to work properly. It seems able to delete some numbers, but not any number you pass into the function. Could anyone experienced with C take a look and possibly point out where I went wrong? I have been working on this for a while now and have not had much luck and I have started over 3 times :( Any help is much appreciated. Thank you. You can see my first attempt of code here. I can only post one link, so if you would like to see my second attempt, just tell me so and I can email it to you or something. Thank you for your time.

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  • TStringList, Dynamic Array or Linked List in Delphi?

    - by lkessler
    I have a choice. I have an array of ordered strings that I need to store and access. It looks like I can choose between using: A TStringList A Dynamic Array of strings, and A Linked List of strings In what circumstances is each of these better than the others? Which is best for small lists (under 10 items)? Which is best for large lists (over 1000 items)? Which is best for huge lists (over 1,000,000 items)? Which is best tor minimize memory use? Which is best to minimize loading and/or access time? For reference, I am using Delphi 2009.

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