Remove a loop from a linked list

removeloop.cpp

bool has_cycle(node* head) {
  if (!head || !head->next) return false;
  node* slow, *fast;
  slow = fast = head;
  while (true) {
    slow = slow->next;
    if (fast->next)
      fast = fast->next->next;
    if (slow == nullptr || fast == nullptr)
      return false;
    if (slow == fast) {
      return slow->next != nullptr;
    }
  }
}

void remove_cycle(node* head) {
  if (!head || !head->next) return;
  node* slow, *fast;
  slow = fast = head;
  while (true) {
    slow = slow->next;
    if (fast->next)
      fast = fast->next->next;
    if (slow == fast) {
      if (slow != nullptr)
        slow->next = nullptr;
      return;
    }
  }
}

The loop is always located at the tail of the list. The trick is to move the fast pointer first before checking if both pointers are the same.