Deleting duplicates in a linked list

This is a discussion on Deleting duplicates in a linked list within the C++ Programming forums, part of the General Programming Boards category; I need to create a function that deletes the duplicates from a linked list this , I think looks right ...

  1. #1
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    Deleting duplicates in a linked list

    I need to create a function that deletes the duplicates from a linked list this , I think looks right but it causes an application error saying the memory at a certain location could not be read

    void delrep (node *&head)
    { node *previous = head;

    for (node *head2 = head ; head2->link != NULL;head2=head2->link)
    {

    for (node *compare =head->link;compare ->link !=NULL; compare=compare ->link)
    {

    if ( compare ->data == head2->data)
    {

    previous->link = compare->link;

    delete compare;

    if(compare->link == NULL)

    break;

    }

    previous = compare;

    }

    }

    }
    Any ideas whats wrong with it?

  2. #2
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    first guess--look at the lines below as copied from posted code:

    delete compare;

    if(compare->link == NULL)

    break;

    }

    previous = compare;


    Now ask yourself what is the value of compare->link and compare after compare is deleted?????

  3. #3
    Banned Troll_King's Avatar
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    Is this an ordered list? You might have an easier time getting rid of duplicates in a sorting algorithm.

  4. #4
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    Is it possible to stp the pointer at the node before the one I want to delete like loop until the pointer ->link-> data, sort of.I need to create a pointer pointing at the node before the one I want to remove. How?

  5. #5
    zen
    zen is offline
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    I'm not sure what you mean, but if you want to traverse the list backwards then you can either make your list doubly linked, or use a further copy(iterator) of the head node to traverse your list until iterator->next is equal to the node that you require the previous node. Something like -

    node* iterator = head;
    node* prevnode;

    while(iterator->next!=compare)
    iterator=iterator->next;

    prevnode=iterator;
    zen

  6. #6
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    is this any closer

    void delrep (node *&head)
    { node *remove = head;

    for (node *head2 = head ; head2->link != NULL;head2=head2->link)
    {
    int i =1;
    for (node *compare =head->link;compare ->link !=NULL; compare=compare ->link)
    { i++;

    if ( compare ->data == head2->data)
    { node *bridge = head ;
    for( int x =1 ;x < i-1; x++)
    {
    bridge = bridge ->link;
    }

    remove->link = compare->link;
    bridge ->link = compare ->link ;

    delete remove;

    //if(compare->link == NULL)

    //break;

    }

    //previous = compare;

    }

    }

    }

  7. #7
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    Zen,
    I tried adding your code , I get some error message when I run it

    did I add it right?

    void delrep (node *head)
    { node *remove = head;

    node *head2;
    head2 = head;
    while (head2->link!=NULL)
    {

    for (node *compare =head;compare ->link !=NULL; compare=compare ->link)
    {


    if ( compare ->data == head2->data)
    {
    node* iterator = head;
    node* prevnode;
    prevnode = new node;

    if (iterator != NULL)
    {
    while(iterator->link!=compare)
    iterator=iterator->link;
    };

    prevnode=iterator;

    compare->link= remove ;
    prevnode ->link = compare ->link ;

    delete remove;
    remove = NULL;


    }

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