Merge a linked list into another linked list at alternate positions in Java

We are given two data structures as linked list Let’s say, List_1 and List_2. The task is to merge the elements of linked list ‘List_2’ into the linked list ‘List_1’ at an alternate position and if we are left with the elements which can't be merged into ‘List_1’ then it will be printed as the ‘List_2’ remaining elements.

For Example-:

In −

List_1 =

List_2 =

Out − Merged List is-:

Explanation − we are given with two lists i.e. List_1 and List_2. We had merged the possible elements of list_2 into List_1 at alternate positions. So, elements after merging in List_1 are 10- >3->2->1->1->4->2->5->5 and in List_2 are 7->2.

In −

List_1 = 11 -> 12 -> 13

List_2 = 14 -> 15 -> 16 -> 17 -> 18

Out −Merged List is -: 11 -> 14 -> 12 -> 15 -> 13

Explanation −we are given with two lists i.e. List_1 and List_2. We had merged the possible elements of list_2 into List_1 at alternate positions. So, elements after merging in List_1 are 11 - > 14 -> 12 -> 15 -> 13 and in List_2 are 16->17->18.

Approach used in the below program is as follows −

• Create a head node that will point to the first node of a linked list.

• Create a class of Node to create the linked list which will have value and next as data members. Define a default constructor as Node(int val) and set value as val and next as NULL.

• Inside a method in add(int updated_value) to add the elements to a linked list.

  • Create an object as new_node and pass updated_value to the default constructor.

  • Set new_node.next to head and head to new_node

• Inside a function in mergeList(TutorialPoint list)

  • Create an object as n1_curr and set to head and n2_curr to list.head

  • Create an object as n1_next and n2_next

  • Start While as n1_curr != null AND n2_curr != null. Inside the While set n1_next to n1_curr.next, n2_next to n2_curr.next, n2_curr.next to n1_next, n1_curr.next to n2_curr, n1_curr to n1_next and n2_curr to n2_next

  • Set list.head to n2_curr

• Inside the main() method

  • Create an object as TutorialPoint list_1 to new TutorialPoint() and TutorialPoint list_2 to new TutorialPoint()

  • Add elements to list_1 as list_1.add(13), list_1.add(12) and list_1.add(11).

  • Add elements to list_2 as list_2.add(18), list_2.add(17), list_2.add(16), list_2.add(15) and list_2.add(14)

  • Call the mergeList method to merge the elements of list_2 to list_1 as list_1.mergeList(list_2)

  • Print the final list as an output.

Example

public class TutorialPoint{
   Node head;
   class Node{
      int value;
      Node next;
      Node(int val){
         value = val;
         next = null;
      }
   }
   void add(int updated_value){
      Node new_node = new Node(updated_value);
      new_node.next = head;
      head = new_node;
   }
   void mergeList(TutorialPoint list){
      Node n1_curr = head, n2_curr = list.head;
      Node n1_next, n2_next;

      while (n1_curr != null && n2_curr != null){
         n1_next = n1_curr.next;
         n2_next = n2_curr.next;

         n2_curr.next = n1_next;
         n1_curr.next = n2_curr;

         n1_curr = n1_next;
         n2_curr = n2_next;
      }
      list.head = n2_curr;
   }
   public static void main(String args[]){
      TutorialPoint list_1 = new TutorialPoint();
      TutorialPoint list_2 = new TutorialPoint();
      list_1.add(13);
      list_1.add(12);
      list_1.add(11);
      list_2.add(18);
      list_2.add(17);
      list_2.add(16);
      list_2.add(15);
      list_2.add(14);
      list_1.mergeList(list_2);
      System.out.println("Merged list is:");
      Node temp = list_1.head;
      while (temp != null){
         System.out.print(temp.value + " ");
         temp = temp.next;
      }
      System.out.println();
   }
}

Output

If we run the above code it will generate the following Output

Merged list is:
11 14 12 15 13 16