C++将二叉树转为双向链表及判断两个链表是否相交

List * isJoined(List * h1,List * h2)
{
  List * ph1,*p1,*p2;
  int flag;
 
  ph1 = h1; 
  while(ph1->next != NULL)
    ph1 = ph1->next;  
  ph1->next = h2;
 
  if(0 == isCycle(h1))
  {
    flag = 0;
  }
  else
  {
    p1 = h1;
    while(p1 != p2)
    {
      p1 = p1->next;
      p2 = p2->next;
    }
    flag = p1;
  }
   
  return flag;
}