If we have two sorted linked list and we want to merge both in a new list without creating new node space then we can use recursive approach for this . This approach takes O(max(m,n)) time complexity for merging.

Like we have a linked list named : list 1 1 -> 2 -> 3 -> 4

and another list named : list2 5 -> 6 -> 7

then resulting linked list will be 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7

here is an coding example for merge operation :

public Node<T> mergeLinkedList(Node<T> list1, Node<T> list2)
{
   if(list1 == null){
       return list2;
    }

   if(list2 == null){
       return list1;
    }

   if(list1.getValue() < list2.getValue()){
      list1.next = mergeLinkedList(list1.next , list2);
      return list1;
   }else{
      list2.next = mergeLinkedList(list2.next , list1);
      return list2;
    }
}