loopinlinkedlist.c

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


struct Node
{
	int data;
	struct Node* next;
};

int countNodes(struct Node *n)
{
int res = 1;
struct Node *temp = n;
while (temp->next != n)
{
	res++;
	temp = temp->next;
}
return res;
}

int countNodesinLoop(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)
			return countNodes(slow_p);
	}

	return 0;
}

struct Node *newNode(int key)
{
	struct Node *temp =
		(struct Node*)malloc(sizeof(struct Node));
	temp->data = key;
	temp->next = NULL;
	return temp;
}


int main()
{
	struct Node *head = newNode(1);
	head->next = newNode(2);
	head->next->next = newNode(3);
	head->next->next->next = newNode(4);
	head->next->next->next->next = newNode(5);

	head->next->next->next->next->next = head->next;

	printf("%d \n", countNodesinLoop(head));

	return 0;
}