In the case of an even number of elements in the linked list, we can easily split the list into two halves.

Store the mid and last pointers of the circular linked list using the tortoise and hare algorithm. Now, make the second half circular and the first half circular. Set the head (or start ) pointers of the two linked lists.

When there is an odd number of elements in a linked list, then we will have one more node in the first list then the second list.

In C++

#include <bits/stdc++.h>
using namespace std;

class Node
{
	public:
	int data;
	Node *next;
};

void splitList(Node *head, Node **head1_ref,
						Node **head2_ref)
{
	Node *slow_ptr = head;
	Node *fast_ptr = head;
	
	if(head == NULL)
		return;
	
	/* If there are odd nodes in the circular list then
	fast_ptr->next becomes head and for even nodes
	fast_ptr->next->next becomes head */
	while(fast_ptr->next != head &&
		fast_ptr->next->next != head)
	{
		fast_ptr = fast_ptr->next->next;
		slow_ptr = slow_ptr->next;
	}
	
	/* If there are even elements in list
	then move fast_ptr */
	if(fast_ptr->next->next == head)
		fast_ptr = fast_ptr->next;
		
	/* Set the head pointer of first half */
	*head1_ref = head;
		
	/* Set the head pointer of second half */
	if(head->next != head)
		*head2_ref = slow_ptr->next;
		
	/* Make second half circular */
	fast_ptr->next = slow_ptr->next;
		
	/* Make first half circular */
	slow_ptr->next = head;
}


void push(Node **head_ref, int data)
{
	Node *ptr1 = new Node();
	Node *temp = *head_ref;
	ptr1->data = data;
	ptr1->next = *head_ref;
		
	/* If linked list is not NULL then
	set the next of last node */
	if(*head_ref != NULL)
	{
		while(temp->next != *head_ref)
		temp = temp->next;	
		temp->next = ptr1;
	}
	else
		ptr1->next = ptr1; /*For the first node */
	
	*head_ref = ptr1;
}


void printList(Node *head)
{
	Node *temp = head;
	if(head != NULL)
	{
		cout << endl;
		do {
		cout << temp->data << " ";
		temp = temp->next;
		} while(temp != head);
	}
}

int main()
{
	int list_size, i;
		
	/* Initialize lists as empty */
	Node *head = NULL;
	Node *head1 = NULL;
	Node *head2 = NULL;
	
	push(&head, 1);
	push(&head, 5);
	push(&head, 2);
	push(&head, 10);
	
	cout << "Original Circular Linked List";
	printList(head);	
	
	splitList(head, &head1, &head2);
	
	cout << "\nFirst Circular Linked List";
	printList(head1);
	
	cout << "\nSecond Circular Linked List";
	printList(head2);
	return 0;
}

The Output

Original Circular Linked List

10 2 5 1

First Circular Linked List

10 2

Second Circular Linked List

5 1

In C

#include<stdio.h>
#include<stdlib.h>

/* structure for a node */
struct Node
{
int data;
struct Node *next;
};


void splitList(struct Node *head, struct Node **head1_ref,
									struct Node **head2_ref)
{
struct Node *slow_ptr = head;
struct Node *fast_ptr = head;

if(head == NULL)
	return;

/* If there are odd nodes in the circular list then
	fast_ptr->next becomes head and for even nodes
	fast_ptr->next->next becomes head */
while(fast_ptr->next != head &&
		fast_ptr->next->next != head)
{
	fast_ptr = fast_ptr->next->next;
	slow_ptr = slow_ptr->next;
}

/* If there are even elements in list then move fast_ptr */
if(fast_ptr->next->next == head)
	fast_ptr = fast_ptr->next;	
	
/* Set the head pointer of first half */
*head1_ref = head;	
	
/* Set the head pointer of second half */
if(head->next != head)
	*head2_ref = slow_ptr->next;
	
fast_ptr->next = slow_ptr->next;
	
slow_ptr->next = head;	
}

void push(struct Node **head_ref, int data)
{
struct Node *ptr1 = (struct Node *)malloc(sizeof(struct Node));
struct Node *temp = *head_ref;
ptr1->data = data;
ptr1->next = *head_ref;
	
if(*head_ref != NULL)
{
	while(temp->next != *head_ref)
	temp = temp->next;		
	temp->next = ptr1;
}
else
	ptr1->next = ptr1; /*For the first node */

*head_ref = ptr1;	
}


void printList(struct Node *head)
{
struct Node *temp = head;
if(head != NULL)
{
	printf("\n");
	do {
	printf("%d ", temp->data);
	temp = temp->next;
	} while(temp != head);
}
}
int main()
{
int list_size, i;
	
struct Node *head = NULL;
struct Node *head1 = NULL;
struct Node *head2 = NULL;

push(&head, 12);
push(&head, 56);
push(&head, 2);
push(&head, 11);

printf("Original Circular Linked List");
printList(head);	

/* Split the list */
splitList(head, &head1, &head2);

printf("\nFirst Circular Linked List");
printList(head1);

printf("\nSecond Circular Linked List");
printList(head2);
	
getchar();
return 0;
}

The output:

Original Circular Linked List

11 2 56 12

First Circular Linked List

11 2

Second Circular Linked List

56 12

In Python

class Node:
	
	# Constructor to create a new node
	def __init__(self, data):
		self.data = data
		self.next = None


# Class to create a new Circular Linked list
class CircularLinkedList:
	
	# Constructor to create a empty circular linked list
	def __init__(self):
		self.head = None

	# Function to insert a node at the beginning of a
	# circular linked list
	def push(self, data):
		ptr1 = Node(data)
		temp = self.head
		
		ptr1.next = self.head

		# If linked list is not None then set the next of
		# last node
		if self.head is not None:
			while(temp.next != self.head):
				temp = temp.next
			temp.next = ptr1

		else:
			ptr1.next = ptr1 # For the first node

		self.head = ptr1

	# Function to print nodes in a given circular linked list
	def printList(self):
		temp = self.head
		if self.head is not None:
			while(True):
				print ("%d" %(temp.data),end=' ')
				temp = temp.next
				if (temp == self.head):
					break


	# Function to split a list (starting with head) into
	# two lists. head1 and head2 are the head nodes of the
	# two resultant linked lists
	def splitList(self, head1, head2):
		slow_ptr = self.head
		fast_ptr = self.head
	
		if self.head is None:
			return
		
		# If there are odd nodes in the circular list then
		# fast_ptr->next becomes head and for even nodes
		# fast_ptr->next->next becomes head
		while(fast_ptr.next != self.head and
			fast_ptr.next.next != self.head ):
			fast_ptr = fast_ptr.next.next
			slow_ptr = slow_ptr.next

		# If there are even elements in list then
		# move fast_ptr
		if fast_ptr.next.next == self.head:
			fast_ptr = fast_ptr.next

		# Set the head pointer of first half
		head1.head = self.head

		# Set the head pointer of second half
		if self.head.next != self.head:
			head2.head = slow_ptr.next

		# Make second half circular
		fast_ptr.next = slow_ptr.next
	
		# Make first half circular
		slow_ptr.next = self.head


head = CircularLinkedList()
head1 = CircularLinkedList()
head2 = CircularLinkedList()

head.push(12)
head.push(56)
head.push(2)
head.push(11)

print ("Original Circular Linked List")
head.printList()

head.splitList(head1 , head2)

print ("\nFirst Circular Linked List")
head1.printList()

print ("\nSecond Circular Linked List")
head2.printList()

The output:

Original Circular Linked List

11 2 56 12

First Circular Linked List

11 2

Second Circular Linked List

56 12

In Java

class LinkedList {

	static Node head, head1, head2;

	static class Node {

		int data;
		Node next, prev;

		Node(int d) {
			data = d;
			next = prev = null;
		}
	}

	/* Function to split a list (starting with head) into two lists.
	head1_ref and head2_ref are references to head nodes of
	the two resultant linked lists */
	void splitList() {
		Node slow_ptr = head;
		Node fast_ptr = head;

		if (head == null) {
			return;
		}

		/* If there are odd nodes in the circular list then
		fast_ptr->next becomes head and for even nodes
		fast_ptr->next->next becomes head */
		while (fast_ptr.next != head
				&& fast_ptr.next.next != head) {
			fast_ptr = fast_ptr.next.next;
			slow_ptr = slow_ptr.next;
		}

		/* If there are even elements in list then move fast_ptr */
		if (fast_ptr.next.next == head) {
			fast_ptr = fast_ptr.next;
		}

		/* Set the head pointer of first half */
		head1 = head;

		/* Set the head pointer of second half */
		if (head.next != head) {
			head2 = slow_ptr.next;
		}
		/* Make second half circular */
		fast_ptr.next = slow_ptr.next;

		/* Make first half circular */
		slow_ptr.next = head;
	}

	/* Function to print nodes in a given singly linked list */
	void printList(Node node) {
		Node temp = node;
		if (node != null) {
			do {
				System.out.print(temp.data + " ");
				temp = temp.next;
			} while (temp != node);
		}
	}

	public static void main(String[] args) {
		LinkedList list = new LinkedList();

		
		list.head = new Node(12);
		list.head.next = new Node(56);
		list.head.next.next = new Node(2);
		list.head.next.next.next = new Node(11);
		list.head.next.next.next.next = list.head;

		System.out.println("Original Circular Linked list ");
		list.printList(head);

		list.splitList();
		System.out.println("");
		System.out.println("First Circular List ");
		list.printList(head1);
		System.out.println("");
		System.out.println("Second Circular List ");
		list.printList(head2);
		
	}
}

The output:

Original Circular Linked List

11 2 56 12

First Circular Linked List

11 2

Second Circular Linked List

56 12

Time and Space Complexity

Time Complexity: O(n) As we are only moving once through the list

Auxiliary Space: O(1) As no extra space is required

Split the Circular Linked List into two halves in C/C++/Java/Python

In C++

In C

In Python

In Java

Time and Space Complexity

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In C++

In C

In Python

In Java

Time and Space Complexity

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