class Link():def __init__(self):#永远指向链表中第一个节点self._head = Nonedef isEmpty(self):return self._head is Nonedef add(self,item):node = Node(item)node.next = self._headself._head = nodedef length(self):count = 0if self.isEmpty():return countelse:cur = self._headwhile cur is not None:count += 1cur = cur.nextreturn countdef travel(self):cur = self._headwhile cur is not None:print(cur)cur = cur.nextdef append(self,item):node = Node(item)cur = self._headif self.isEmpty():self._head = nodeelse:while cur is not None:#因为循环遍历结束后cur会指向空并非最后一个节点pre_cur = curcur = cur.nextpre_cur.next = nodedef search(self,item):ex = Falsecur = self._headwhile cur is not None:if cur.item == item:ex = Truebreakcur = cur.nextreturn exdef insertTo(self,item,index):cur = self._headex = 0node = Node(item)#插入到第一个节点位置if index <= 0:self.add(item)#插入到最后一个节点位置elif index >= self.length():self.append(item)else:while cur is not None:pre = cur cur = cur.next#此处插入的一定不是第一个节点和最后一个节点位置，因此index要减1if ex == index-1:node.next = curpre.next = nodebreakex += 1def remove(self,item):pre = Nonecur = self._head#删除的是第一个节点if cur.item == item:self._head = cur.nextelse:while cur is not None:pre = curcur = cur.nextif cur.item == item:pre.next = cur.nextcur.next = Nonecur = cur.next

    def getlinkloopstart(self):if self._head is None:return Nonefirst = self._headsecond = self._headwhile first.next is not None and second.next is not None:first = first.next.nextsecond = second.nextif first == second:breakif first == second:second = self._headwhile first != second:first = first.nextsecond = second.nextreturn secondelse:return None