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  1. Practice
  2. Data Structures
  3. Linked Lists
  4. Insert a Node at the Tail of a Linked List
  5. Discussions

Insert a Node at the Tail of a Linked List

  • Elnaz + 4 comments

    Java implementation :

    if (head == null){
        head = new Node();
        head.data = data;
    }
    else {
        Node node = head;
        while (node.next != null){
            node = node.next;
        }
        node.next = new Node();
        node.next.data = data;
    }
    return head;
    • shahab03 + 1 comment

      what does this do?

      while (node.next != null){ node = node.next; }

      and why is it needed?

      • Elnaz + 0 comments

        The while loop first check if current node next is not null, it traverse the current node to the second node and when current node next become null, current node point to the last node!

    • The_Speck + 2 comments

      Why must you declare a "Node node = head"? Initially I had:

      if(head == null)
    {
        head = new Node();
        head.data = data;
    }
    else{
        while(head.next != null) head = head.next;
        head.next = new Node();
        head.next.data = data;
    }
    return head;

      But this method doesn't work. May you explain why? Thank you!

      • sanipatel2141 + 1 comment

        because the question asks to "return the head of the updated linked list". In your case you're returning the pointer (is that correct Java terminology?) to the last node.

        • vishaltk + 0 comments

          I did the same mistake, initially and was scratching my head to figured where I went wrong. Hence people say understanding the requirement is important. You may right functionally correct code, but if that is not meeting the requirement, then the whole purpose of your program/app is defeated.

      • amstoler + 1 comment

        CORRECTION to above code For Java 8

        public static Node insert(Node head,int data) { //Complete this method if (head == null){ head = new Node(data); head.data = data; } else { Node node = head; while (node.next != null){ node = node.next; } node.next = new Node(data); node.next.data = data; } return head;
        }

        Make sure to pass by value the int data when creating a new instance of Node. The constructor in class Node (line 7 of code) demands that you specify an int when creating a new Node object. Remember a class constructor is the blueprint for stating what parameters (requirements) an object needs before it can be created. Coded for us already is the method signature of our insert function, which tells us that we already have an int data availabe for us to use. It's being passed by value into the funtion. So make sure that this is the value used when creating new Node objects.

        Thank you to Elnaz for your contribution. I was stuck on this one for a while and could not have solved this without you.

        • faizk6797 + 0 comments

          That was really helpful..Thank u so much

    • haripriya_sreer1 + 1 comment
      [deleted]
      • shaikhkamal2012 + 0 comments

        Hope this will work in c SinglyLinkedListNode *ptr,*tmp; tmp = (SinglyLinkedListNode *)malloc(sizeof(SinglyLinkedListNode)); tmp->data = data;

        if(head==NULL){
    head=tmp;
    tmp->next = NULL;
    return head;
}
else{
    ptr=head;
    while(ptr->next!= NULL)
        ptr=ptr->next;
    ptr->next = tmp;
    tmp->next = NULL;
}

return head;
    • cmveal + 1 comment

      Better to track the last node rather than constantly looping over the list.

      static SinglyLinkedListNode last = null;

static SinglyLinkedListNode insertNodeAtTail(SinglyLinkedListNode head, int data) {
    SinglyLinkedListNode newNode = new SinglyLinkedListNode(data);
    if (head == null) {
        head = newNode;
        last = newNode;
    } else {
        last.next = newNode;
        last = newNode;
    }
    return head;
}
      • sdavis12300 + 0 comments

        What is the last.next = newNode line doing? Shouldn't the last element's next be null?