removing duplicates from a linked list

This is a discussion on removing duplicates from a linked list within the C++ Programming forums, part of the General Programming Boards category; I am trying to write a function that removes duplicates from a linked list. Here is the code I have: ...

  1. #1
    Registered User brianptodd's Avatar
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    Oct 2002
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    66

    removing duplicates from a linked list

    I am trying to write a function that removes duplicates from a linked list.

    Here is the code I have:

    Code:
    /*
     * Function remove_dups()
     *
     * This function removes all duplicates from the list. Any node that is
     * removed is also freed.
     *
     */
    
    void linklist::remove_dups()
    {
    	node * current_ptr;
    	node * prev_ptr;
    	node * temp_ptr;
    
    	current_ptr = _first_element;
    	temp_ptr = _first_element->next;
    
    	while (current_ptr != _last_element)
    	{
    		if (occurrences(current_ptr->data) == 1 && current_ptr->next != NULL)
    		{
    			current_ptr = current_ptr->next;
    		}
    
    		while (temp_ptr->data != current_ptr->data && temp_ptr->next != NULL)
    		{
    			temp_ptr = temp_ptr->next;
    
    			if (temp_ptr == NULL)
    			{
    				current_ptr = current_ptr->next;
    				break;
    			}
    
    		}
    
    		if (current_ptr == _last_element)
    			break;
    
    		if (temp_ptr->data == current_ptr->data)
    		{
    			prev_ptr = _first_element;
    
    			while (prev_ptr->next!= temp_ptr)
    			{
    				prev_ptr = prev_ptr->next;
    			}
    			prev_ptr->next = temp_ptr->next;
    			_remove(temp_ptr);
    			temp_ptr = _first_element;
    		}
    
    	}
    
    }
    If my input is 1,2,3,1,2,3 this function will remove the 1 and the 2, but will leave the duplicate 3. So my output will be 1,2,3,3.

    Any ideas why this is happening?

    Brian
    "In theory, there is no difference between theory and practice. But, in practice, there is."
    - Jan L.A. van de Snepscheut

  2. #2
    Disturbed Boy gustavosserra's Avatar
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    Apr 2003
    Posts
    244
    To tell the truth, I didnīt understand your algorithm very well, I would have done different. Anyway, I noticed the condition of your main loop: while (current_ptr != _last_element). But if _last_element really points to the last element, you will never compare him to other elements, but I may have understood really bad your algorithm!
    I would do like this:
    Code:
    void linklist::remove_dups()
    {
       node* current = _first_element;
       node* next_nd;
       node* previous;
    
       while( current != NULL ){
    
          next_nd = current->next;
          previous = current;
    
          while( next_nd != NULL ){
             if( next_nd->data == current->data){
                previous->next = next_nd->next;
                delete next_nd;
                next_nd = previous->next;
             }
             else{
                previous = next_nd;
                next_nd = next_nd->next;
             }
          }
          current = current->next;
    }
    I have made a quick example, just to show that really works :P
    Hope that helped!
    Attached Files Attached Files
    Nothing more to tell about me...
    Happy day =)

  3. #3
    Registered User brianptodd's Avatar
    Join Date
    Oct 2002
    Posts
    66

    thanks

    That helped a lot. I need to use a member function to perform the actual removing, but your algorithm helped me get mine straight.

    Thanks.

    Brian
    "In theory, there is no difference between theory and practice. But, in practice, there is."
    - Jan L.A. van de Snepscheut

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