Merge two sorted linked lists such that merged list is in reverse order

// C# program to merge two sorted 
// linked list such that merged 
// list is in reverse order

// Linked List Class
using System;

class LinkedList
{

    public Node head; // head of list
    static Node a, b;

    /* Node Class */
    public class Node
    {
        public int data;
        public Node next;

        // Constructor to create a new node
        public Node(int d)
        {
            data = d;
            next = null;
        }
    }

    void printlist(Node node) 
    {
        while (node != null)
        {
            Console.Write(node.data + " ");
            node = node.next;
        }
    }

    Node sortedmerge(Node node1, Node node2)
    {
        
        // if both the nodes are null
        if (node1 == null && node2 == null)
        {
            return null;
        }

        // resultant node
        Node res = null;

        // if both of them have nodes 
        // present traverse them
        while (node1 != null && node2 != null)
        {

            // Now compare both nodes current data
            if (node1.data <= node2.data)
            {
                Node temp = node1.next;
                node1.next = res;
                res = node1;
                node1 = temp;
            } 
            else 
            {
                Node temp = node2.next;
                node2.next = res;
                res = node2;
                node2 = temp;
            }
        }

        // If second list reached end, but first
        // list has nodes. Add remaining nodes of 
        // first list at the front of result list
        while (node1 != null) 
        {
            Node temp = node1.next;
            node1.next = res;
            res = node1;
            node1 = temp;
        }

        // If first list reached end, but second 
        // list has node. Add remaining nodes of 
        // first list at the front of result list
        while (node2 != null)
        {
            Node temp = node2.next;
            node2.next = res;
            res = node2;
            node2 = temp;
        }

        return res;

    }

    // Driver code
    public static void Main(String[] args) 
    {

        LinkedList list = new LinkedList();
        Node result = null;

        /*Let us create two sorted linked lists to test
        the above functions. Created lists shall be
        a: 5->10->15
        b: 2->3->20*/
        LinkedList.a = new Node(5);
        LinkedList.a.next = new Node(10);
        LinkedList.a.next.next = new Node(15);

        LinkedList.b = new Node(2);
        LinkedList.b.next = new Node(3);
        LinkedList.b.next.next = new Node(20);

        Console.WriteLine("List a before merge :");
        list.printlist(a);
        Console.WriteLine("");
        Console.WriteLine("List b before merge :");
        list.printlist(b);

        // merge two sorted linkedlist in decreasing order
        result = list.sortedmerge(a, b);
        Console.WriteLine("");
        Console.WriteLine("Merged linked list : ");
        list.printlist(result);

    }
}

// This code has been contributed by 29AjayKumar

using System;

// Linked list node
public class Node {
    public int data;
    public Node next;
}

public class Program {
    // Given two non-empty linked lists 'a' and 'b',
    // merge them in such a way that the result list
    // will be in reverse order
    public static Node MergeListsReverse(Node a, Node b) {
        Node head = null;  // head of the merged list
        Node tail = null;  // tail of the merged list

        while (a != null && b != null) {
            if (a.data < b.data) {
                Node temp = a.next;
                a.next = head;
                head = a;
                a = temp;
            } else {
                Node temp = b.next;
                b.next = head;
                head = b;
                b = temp;
            }
        }

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

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

        return head;
    }

    // Utility function to insert a node at the beginning of a linked list
    public static void Push(ref Node headRef, int newData) {
        Node newNode = new Node();
        newNode.data = newData;
        newNode.next = headRef;
        headRef = newNode;
    }

    // Utility function to print a linked list
    public static void PrintList(Node head) {
        while (head != null) {
            Console.Write(head.data + " ");
            head = head.next;
        }
        Console.WriteLine();
    }

    // Driver program to test above functions
    public static void Main() {
        Node headA = null;
        Node headB = null;

        // Populate list A
        Push(ref headA, 15);
        Push(ref headA, 10);
        Push(ref headA, 5);

        // Populate list B
        Push(ref headB, 20);
        Push(ref headB, 3);
        Push(ref headB, 2);

        Console.Write("List A before merge: ");
        PrintList(headA);

        Console.Write("List B before merge: ");
        PrintList(headB);

        // Merge the two lists in reverse order
        Node merged = MergeListsReverse(headA, headB);

        Console.Write("Merged list in reverse order: ");
        PrintList(merged);
    }
}