Split a Circular Linked List into two halves | GeeksforGeeks

1) Store the mid and last pointers of the circular linked list using tortoise and hare algorithm.
2) Make the second half circular.
3) Make the first half circular.
4) Set head (or start) pointers of the two linked lists.

oid 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;

  /* Make second half circular */  

  fast_ptr->next = slow_ptr->next;

  /* Make first half circular */  

  slow_ptr->next = head;      

}

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