Question

public class SinglyLikedList {
   private class Node{
       public int item;
       public Node next;
       public Node(int item, Node next) {
           this.item = item;
           this.next = next;
       }
   }
  
   private Node first;
   public void addFirst(int a) {
       first = new Node(a, first);
   }

}

1. Write the method add(int item, int position), which takes an item and a position, and adds a new item at the provided position. For example, suppose that SinglyLikedList is 5->10->3->15, add(22, 4), the resulting list should be 5->10->3->15->22.

2. Write the method reverseList() for the SinglyLikedList that returns the items in a reverse order. For example, given 5->10->3->15->22, the resulting list should be 22->15->3->10->5.

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. If not, PLEASE let me know before you rate, I’ll help you fix whatever issues. Thanks

Note: I have changed the class name from SinglyLikedList to SinglyLinkedList. You may use whichever name you want. But make sure to update it everywhere.

//SinglyLinkedList.java (name corrected)

public class SinglyLinkedList {

      private class Node {

            public int item;

            public Node next;

            public Node(int item, Node next) {

                  this.item = item;

                  this.next = next;

            }

      }

      private Node first;

      public void addFirst(int a) {

            first = new Node(a, first);

      }

      // method to add item to index=position

      public void add(int item, int position) {

            // if position is negative, exiting method

            if (position < 0) {

                  return;

            }

            // if posi8tion is 0, adding new node before current first

            if (position == 0) {

                  first = new Node(item, first);

                  return;

            }

            // else taking a reference to first

            Node temp = first;

            // advancing it position-1 times. or until temp is null, whichever comes

            // first

            for (int i = 0; i < position - 1 && temp != null; i++) {

                  temp = temp.next;

            }

            // if temp is null, that means position is invalid, in which case we

            // simply exit the method

            if (temp == null) {

                  return;

            }

            // else adding new node between temp and temp.next

            temp.next = new Node(item, temp.next);

      }

      // method to return a reversed list

      public SinglyLinkedList reverseList() {

            // creating a SinglyLinkedList

            SinglyLinkedList result = new SinglyLinkedList();

            // looping through each node in this list

            for (Node n = first; n != null; n = n.next) {

                  // adding data of this node before the current first element of the

                  // result list

                  result.first = new Node(n.item, result.first);

            }

            // returning reversed list

            return result;

      }

}