面试题快慢链表和快慢指针

int GetMidNode(LinkList *L,int elem){
  LinkList *search,*mid;
  mid = search = L; //指向头结点
  while (search->next != NULL){ //当存在下个结点的时候 
    if (search->next->next!=NULL) {//检查下个的下个节点是否为空 
      search = search->next->next;
      mid = mid->next;
    } 
    else
      search = search->next;
  }
  elem = mid->data;
  return elem;
}