Following is C code snippet for detecting a cycle in a singly linked list

loop.c

/*The structure of linked list is the following
struct node
{
int data;
node* next;
};*/
int detectloop(struct node *list){
// your code goes here
     if(list==0)
       return  0;
    if(list->data==-1)
      return 1;
    list->data  = -1;
    return detectloop(list->next);
}

This is simple method to detect cycle in the singly linked list . There is floyd's cycle detecting algorithm , but this is simpler and elegant.
The data in each node can also be restored back using one extra variable . Instead of -1 , any other number can be used which is not in the linked list.