Delete Last node of Linked List in Java when the head is not given

Question

I was solving the problem to delete the middle node of a LinkedList. Say given a linked list a->b->c->d->e you would want to delete b/c/d and the head of the LinkedList is not given.

    public boolean deletemiddle(LinkedListNode node) {
        if(node==null)
            return false;
        LinkedListNode n=node;
        node.data=n.next.data;
        node.next=n.next.next;
        return true;
    }

This works. But what if I want to delete the last node e? I know we can do this in c/c++ by manually freeing the space allocated but is it possible to do it in Java? I did try allocating a null to the value but that does not seem to work

if(node.next==null) {
        LinkedListNode dummynode=null;
        node=dummynode;
        return true;
    }

trincot · Accepted Answer · 2022-02-27 07:43:18Z

1

No, this is not possible. You really need a reference to the preceding node so you can update its next reference. A doubly linked list provides such a back reference, but when you are speaking of a singly linked list, the function must get a reference to the preceding node in some other way.

I know we can do this in c/c++ by manually freeing the space allocated

That would not be enough. In C/C++ you also need to set the previous node's next pointer to NULL/nullptr, or else you'll get undefined behaviour. The only thing you can do more in C++ is to pass the previous node's next pointer by reference.

But no matter how you do it, the function must be able to access the next pointer/reference of the preceding node, or it will not be possible.

edited Feb 27, 2022 at 7:43

answered Feb 18, 2022 at 9:25

trincot

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1 Comment

Chaithra Rai Over a year ago

Okay, that explains a lot. Thanks🙂

niklbird · Accepted Answer · 2022-02-17 13:40:38Z

1

If I understand your question correct, you can delete the last node by setting the .next attribute of the previous node to null. If your nodes contain the attribute .previous, you can use that. So

if(node.next==null) {
        node.previous.next = null;
        return true;
}

If you don't have a previous attribute, you need to check for each node if the next node will be the end node. So

if(node.next != null && node.next.next == null){
       node.next = null;
       return true;
}

I hope that answers your question.

answered Feb 17, 2022 at 13:40

niklbird

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