Create mergeSort

mergeSort

@@ -0,0 +1,132 @@
+// C++ program for merge sort on doubly linked list
+#include <bits/stdc++.h>
+using namespace std;
+class Node
+{
+	public:
+	int data;
+	Node *next, *prev;
+};
+
+Node *split(Node *head);
+
+// Function to merge two linked lists
+Node *merge(Node *first, Node *second)
+{
+	// If first linked list is empty
+	if (!first)
+		return second;
+
+	// If second linked list is empty
+	if (!second)
+		return first;
+
+	// Pick the smaller value
+	if (first->data < second->data)
+	{
+		first->next = merge(first->next,second);
+		first->next->prev = first;
+		first->prev = NULL;
+		return first;
+	}
+	else
+	{
+		second->next = merge(first,second->next);
+		second->next->prev = second;
+		second->prev = NULL;
+		return second;
+	}
+}
+
+// Function to do merge sort
+Node *mergeSort(Node *head)
+{
+	if (!head || !head->next)
+		return head;
+	Node *second = split(head);
+
+	// Recur for left and right halves
+	head = mergeSort(head);
+	second = mergeSort(second);
+
+	// Merge the two sorted halves
+	return merge(head,second);
+}
+
+// A utility function to insert a new node at the
+// beginning of doubly linked list
+void insert(Node **head, int data)
+{
+	Node *temp = new Node();
+	temp->data = data;
+	temp->next = temp->prev = NULL;
+	if (!(*head))
+		(*head) = temp;
+	else
+	{
+		temp->next = *head;
+		(*head)->prev = temp;
+		(*head) = temp;
+	}
+}
+
+// A utility function to print a doubly linked list in
+// both forward and backward directions
+void print(Node *head)
+{
+	Node *temp = head;
+	cout<<"Forward Traversal using next pointer\n";
+	while (head)
+	{
+		cout << head->data << " ";
+		temp = head;
+		head = head->next;
+	}
+	cout << "\nBackward Traversal using prev pointer\n";
+	while (temp)
+	{
+		cout << temp->data << " ";
+		temp = temp->prev;
+	}
+}
+
+// Utility function to swap two integers
+void swap(int *A, int *B)
+{
+	int temp = *A;
+	*A = *B;
+	*B = temp;
+}
+
+// Split a doubly linked list (DLL) into 2 DLLs of
+// half sizes
+Node *split(Node *head)
+{
+	Node *fast = head,*slow = head;
+	while (fast->next && fast->next->next)
+	{
+		fast = fast->next->next;
+		slow = slow->next;
+	}
+	Node *temp = slow->next;
+	slow->next = NULL;
+	return temp;
+}
+
+// Driver program
+int main(void)
+{
+	Node *head = NULL;
+	insert(&head, 5);
+	insert(&head, 20);
+	insert(&head, 4);
+	insert(&head, 3);
+	insert(&head, 30);
+	insert(&head, 10);
+	head = mergeSort(head);
+	cout << "Linked List after sorting\n";
+	print(head);
+	return 0;
+}
+
+// This is code is contributed by rathbhupendra