Merge Sort for Doubly Linked List

// C# Program for merge sort
// on doubly linked list

using System;

class Node {
    public int data;
    public Node next;
    public Node prev;

    public Node(int data) {
        this.data = data;
        this.next = null;
        this.prev = null;
    }
}

class GfG {
  
    // Function to split the doubly linked list into two
    // halves
    static Node Split(Node head) {
        Node fast = head;
        Node slow = head;

        // Move fast pointer two steps and slow pointer one
        // step until fast reaches the end
        while (fast != null && fast.next != null
               && fast.next.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }

        // Split the list into two halves
        Node temp = slow.next;
        slow.next = null;
        if (temp != null) {
            temp.prev = null;
        }
        return temp;
    }

    // Function to merge two sorted doubly linked lists
    static Node Merge(Node first, Node second) {
      
        // If either list is empty, return the other list
        if (first == null)
            return second;
        if (second == null)
            return first;

        // Pick the smaller value between first and second
        // nodes
        if (first.data < second.data) {
          
            // Recursively merge the rest of the lists and
            // link the result to the current node
            first.next = Merge(first.next, second);
            if (first.next != null) {
                first.next.prev = first;
            }
            first.prev = null;
            return first;
        }
        else {
            // Recursively merge the rest of the lists and
            // link the result to the current node
            second.next = Merge(first, second.next);
            if (second.next != null) {
                second.next.prev = second;
            }
            second.prev = null;
            return second;
        }
    }

    // Function to perform merge sort on a doubly linked
    // list
    static Node MergeSort(Node head){
      
        // Base case: if the list is empty or has only one
        // node, it's already sorted
        if (head == null || head.next == null) {
            return head;
        }

        // Split the list into two halves
        Node second = Split(head);

        // Recursively sort each half
        head = MergeSort(head);
        second = MergeSort(second);

        // Merge the two sorted halves
        return Merge(head, second);
    }

    static void PrintList(Node head) {
        Node curr = head;
        while (curr != null) {
            Console.Write(curr.data + " ");
            curr = curr.next;
        }
        Console.WriteLine();
    }

    static void Main(string[] args) {
      
      	// Create a hard-coded doubly linked list:
  		// 10 <-> 8 <-> 5 <-> 2
        Node head = new Node(10);
        head.next = new Node(8);
        head.next.prev = head;
        head.next.next = new Node(5);
        head.next.next.prev = head.next;
        head.next.next.next = new Node(2);
        head.next.next.next.prev = head.next.next;

        head = MergeSort(head);
      
        PrintList(head);
    }
}