Question

How to identify linked list is circular? Please share the sample code?

Answer 1

To check whether it is circular or not pass the head or start node address to following function:

void CheckListIsCircularOrNot(struct node *head)
{
    struct node *temp=NULL;
    temp=head;
    while(temp!=NULL)
    {
      if(temp->next==head)
      {
       printf("List is circular ");
       break;
      }
      else
      {
       temp=temp->next;
      }
    }
}

Answer 2

If the last element of linkedlist is not empty but it carries the address of start element ,then our linkedlist will be circular..

Comments

How will u find the last node in circular LL?

---

for eg..

struct node{
int data;
struct node *next;
}; struct node * start=NULL;

void check()
{
struct  node * temp;
temp=start;
while(temp!=NULL)
{
temp=temp->next;
if(temp->next==start)
{
printf("linkedlist is circular");
}
else{
temp=temp->next;
}
}

Answer 3

//Note: Cycle may be generated any node in Linked list , So this problem can be solved by Floyd's cycle finding algorithm
// C program to detect loop in a linked list using Floyd's cycle finding algorithm

int detectcycleinLL(struct node *list)
{
    struct node  *slow_p = list, *fast_p = list;

    while (slow_p && fast_p && fast_p->next )
    {
        slow_p = slow_p->next;
        fast_p  = fast_p->next->next;
        if (slow_p == fast_p)
        {
           printf("Found Loop");
           return 1;
        }
    }
    return 0;
}