Write a Algorithm that counts number of nodes in the circular linked list?

Question

What is the best logic or way to detected linked list has loop ?
And also what is the best way to find out that given linked list is circular ?

Answer 1

Just move one node in a iteration till start node is next node and each iteration increase the count by one.

void count(struct node *last)  //last is the last node
{
    struct node *p;
    int count_node=0;

    if(last==NULL)
    {
       printf("list empty\n");
       return;
    }
    p=last->link;

    do
    {
       count_node++;
       p=p->link;
    }while(p!=last->link);

    printf("\nNo of nodes=%d",count_node);
}

Answer 2

here count gives no of nodes in that list

struct node
{  int data;
   struct node *next;
};
i write just function here
int count(struct node *pp)
{  struct node *start;
  int count=0;
   start=pp->next;
  while(start->next!=pp)
  { start=start->next;  
   count++; }
  return count;
}

Comments

This code will give segmentation fault.If list is empty because you did not check empty case of list

Answer 3

int countNode(struct node*List)
{
struct node*firstNode=List; 
int count=0;
if(List==NULL)
return 0;
while(List->next!=firstNode)
count++,List=List->next;
return coutn;
}