cycle.c

struct node 
{
    int info;
    struct node *next;
};

int cycle(struct node *head)
{
    struct node *slow, *fast;

    if (head == NULL)
        return 0;
    slow = head;
    fast = head->next;
    while (slow != fast && slow != NULL) {
        slow = slow->next;
        if (fast->next->next != NULL)
            fast = fast->next->next;
    }
        
    if (slow == fast)
        return 1;
    else
        return 0;
}