How do you use previous pointer in linked list(doubly)

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So if we are creating a doubly linked list how is previous node managed
where does rear points
in this case I am using rear as current pointer

What I have tried:

node *newnode=new node();
    newnode->v=a;
    if(rear!=NULL)
    {
        rear->next=newnode;
        rear->next->prev=front->next;
        newnode->next=NULL;
        newnode->prev=rear;
        rear=newnode;
    }
    else
    {
        front->next=newnode;
        front->prev=NULL;
        newnode->next=NULL;
        newnode->prev=front;
        rear->prev=front;
        rear=newnode;
    }

Posted 29-Oct-17 10:44am

Member 13455005

Updated 30-Oct-17 0:14am

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2 solutions

Solution 1

You have two pointers in the node, next points to the next node in the list, or NULL if there are no more. previous points to the (obviously) previous node in the list, or NULL if it is the first. You manage your list by initialising a pointer with the address of the first node in the list. As you add or remove nodes, you update their links appropriately.

Posted 29-Oct-17 23:13pm

Richard MacCutchan

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CPallini 30-Oct-17 6:10am

5.

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CPallini · Accepted Answer · 2017-10-30T00:14:00

Richard already gave you the answer.
Please note

Quote:
node *newnode=new node();
newnode->v=a;
if(rear!=NULL)
{
rear->next=newnode;
rear->next->prev=front->next;
newnode->next=NULL;
newnode->prev=rear;
rear=newnode;
}
else
{
front->next=newnode;
front->prev=NULL;
newnode->next=NULL;
newnode->prev=front;
rear->prev=front;//<==== BUG here
rear=newnode;
}

There is a bug in the marked line: you are dereferencing a NULL pointer (rear).