CODEWITHSUNDEEP
javaloopslinked-listnodes
user2124140
user2124140

Reputation:

How do you remove the first Node in a Linked List?

Sup guys so I'm going over a few of my methods in my Linked List class and I'm getting a logical error when removing a node from a linked list. I was working on my removeFirst() method when I then encountered a error in my removeLast() method as well. The problem is that both remove the last item in the list. not sure why but here is my code.

Remove First Node

public T removeFirst() throws EmptyCollectionException
{
 // Checking to see if the List is empty or not
    if ( isEmpty() )
        throw new EmptyCollectionException("LinkedList");

    Node < T > temp  = contents;

    T  next = contents.getNext().getItem();

    contents = new Node ( next, contents );
    count--;

    return temp.getItem();
}



Remove Last Node

public T removeLast() // fixed
{
 // Checking to see if the List is empty or not
    if (isEmpty())
        throw new EmptyCollectionException("LinkedList");

    // Node<T> temp = contents;
    Node<T> current = contents;  
    Node<T> prev = null;        

    while (current.getNext() != null) 
    {
        prev = current; 
        current = current.getNext();
    } 

    prev.setNext(null); 

    count--;

    return current.getItem();

}

I've looked around the questions already posted but I can't seem to find the answer I'm looking for.
I Know that a node has at least two values
one to hold the data and another to hold the reference to the next node

That's what I think is going on for the first one. But when I call the methods one after another they both get rid off the last node. Idk I will look over my code and update this question if necessary. But can you guys see where I'm going wrong and point me in the right direction. Thank you.

Upvotes: 1

Views: 39959

Answers (4)

htkaya
htkaya

Reputation: 245

I think you need to add head node to your linked list class for defining the first node of the list.

public void deleteFront()
{
   if (head!=null){
   head = head.next;
   }
}

Upvotes: 1

Mahmud Hoque
Mahmud Hoque

Reputation: 11

public T removeFirst() throws EmptyCollectionException {
 if (isEmpty())
    throw new EmptyCollectionException("LinkedList");

Node < T > temp  = contents;

T  next = contents.getNext().getItem();

contents = new Node ( next, contents );
count--;



  return temp.getItem();
}

In this method comment last three statement. then add below three lines

contents=contents.getNext()
count--;
return next;

For removing last node: Its looks fine to me.

Upvotes: 0

gifpif
gifpif

Reputation: 4917

public void removeFirst() {
        if (head == null)
              return;
        else {
              if (head == tail) {
                    head = null;
                    tail = null;
              } else {
                    head = head.next;
              }
        }
  }

Upvotes: 2

ValarDohaeris-fuck-OpenAI
ValarDohaeris-fuck-OpenAI

Reputation: 6298

If you have a list A->B->C, A being the head ("contents") of your list, in order to remove it, you simply have to advance the pointer to B, i.e. the next node in your list:

public T removeFirst() throws EmptyCollectionException {
    // Checking to see if the List is empty or not
    if ( isEmpty() )
        throw new EmptyCollectionException("LinkedList");

    Node<T> first = contents;

    contents = contents.getNext();
    count--;

    return first.getItem();
}

Since you also need to return the data associated with the first node, you need to keep a temporary reference to it. (I called it first)

Upvotes: 2

Related Questions