C ++链表将新节点添加到列表的开头

Question

I'm struggling with how to link the new node I am creating to the rest of my linked list.

template <class T>
void LinkedList<T>::addBeg(T value)
{
      ListNode *nodePtr = head;
      head = nodePtr->next;
      head = nodePtr;
      nodePtr = new ListNode(value);
}

I know what I did wrong here: the new value is not associated the linked list at all.

I think I know what I need to do. I'm pretty sure what I need to do is create the new value, insert into the beginning of the existing list, and then redefine head to be the newly created value.

The problem I'm having, is I don't know how to do this.

So, what I think I need to do (at least logically), is set

*nodePtr = new Listnode(value);

Then set

nodePtr = head; 

then set

head = nodePtr-> next; 

and then set the

new ListNode(value) = head;

Am I on the right track? I can't shake the nagging feeling that I'm not correctly linking the new ListNode to the existing list and I can't figure out if I am making the wrong steps or if I'm missing a step.

Answer 1

To create a new node to the head of a list, follow these steps

1. Create a temporary node holding your value
2. Set the temporary node's next to point to the head
3. Set the head to temporary

Answer 2

You first have to create a new Node, then link it to the current head. Then you switch the reference from your previous head to the newly created node.

ListNode *newHead = new ListNode;
newHead->next = head;
head = newHead;

Answer 3

If you say nodePtr = head; then you're just overwriting the pointer you just made. You want to change nodePtr->next = head; head = nodePtr; nodePtr->next = head; head = nodePtr;

Answer 4

Think carefully about what you have and what you need to do:

• You have two nodes that you care about: the current head and your new nodePtr .
• You want nodePtr->next to point to your current head, and update head to point to nodePtr so that this is the first node in the list.

The order in which you do things is important: if you assign the new value of head before making nodePtr->next point to the previous value, you will lose your whole list! Therefore:

1. Create your new node nodePtr .
2. Make nodePtr->next point to head.
3. Make head point to nodePtr

Answer 5

You are on the wrong way. The solution is create the new node, link the next node to head, and after refer the head to new node:

template <class T>
void LinkedList<T>::addBeg(T value)
{
    ListNode *nodePtr = new ListNode(value);
    nodePtr->next = head;
    head = nodePtr;
}