Adding items to end of linked list

Question

I\'m studying for an exam, and this is a problem from an old test:

We have a singly linked list with a list head with the following declaration:

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Answer 1

loop to the last element of the linked list which have next pointer to null then modify the next pointer to point to a new node which has the data=object and next pointer = null

Answer 2

The above programs might give you NullPointerException. This is an easier way to add an element to the end of linkedList.

public class LinkedList {
    Node head;

    public static class Node{
        int data;
        Node next;

        Node(int item){
            data = item;
            next = null;
        }
    }
    public static void main(String args[]){
        LinkedList ll = new LinkedList();
        ll.head = new Node(1);
        Node second = new Node(2);
        Node third = new Node(3);
        Node fourth = new Node(4);

        ll.head.next = second;
        second.next = third;
        third.next = fourth;
        fourth.next = null;

        ll.printList();
        System.out.println("Add element 100 to the last");
        ll.addLast(100);
        ll.printList();
    }
    public void printList(){
        Node t = head;
        while(n != null){
            System.out.println(t.data);
            t = t.next;
        }

    }

    public void addLast(int item){
        Node new_item = new Node(item);
        if(head == null){
            head = new_item;
            return;
        }
        new_item.next = null;

        Node last = head;
        Node temp = null;
        while(last != null){
            if(last != null)
                temp = last;
            last = last.next;
        }   

        temp.next = new_item;   
        return;
    }
}

Answer 3

If you keep track of the tail node, you don't need to loop through every element in the list.

Just update the tail to point to the new node:

AddValueToListEnd(value) {
    var node = new Node(value);

    if(!this.head) {
        this.head = node;
        this.tail = node;
    } else {
        this.tail.next = node; //point old tail to new node
    }
        
    this.tail = node; //now set the new node as the new tail
}

In plain English:

• Create a new node with the given value
• If the list is empty, point head and tail to the new node
• If the list is not empty, set the old tail.next to be the new node
• In either case, update the tail pointer to be the new node