class Node:
  def __init__(self,dataval=None):
    self.dataval=dataval
    self.nextval=None


class SLinkList:
  def __init__(self):
    self.headval=None

  # 遍歷列表
  def traversal_slist(self):
    head_node=self.headval
    while head_node is not None:
      print(head_node.dataval)

      head_node=head_node.nextval


#   表頭插入結點
  def head_insert(self,newdata):
    Newdata=Node(newdata)
    Newdata.nextval=self.headval
    self.headval=Newdata

  # 表尾插入結點
  def tail_insert(self,newdata):
    Newdata=Node(newdata)

    if self.headval is None:
      self.headval=Newdata
      return
    head_node = self.headval
    while head_node.nextval :
      head_node=head_node.nextval
    head_node.nextval=Newdata

#   在兩個數據結點之間插入
  def middle_insert(self,middle_node,newdata):
    Newdata=Node(newdata)
    if middle_node is None:
      return
    Newdata.nextval=middle_node.nextval
    middle_node.nextval=Newdata

#   刪除結點
  def remove_node(self,newdata):
    head_node=self.headval
    if head_node==None:
      return
    if head_node.dataval == newdata:
      self.headval = head_node.nextval
      head_node = None
      return
    while head_node is not None:
      prev=head_node
      head_node=head_node.nextval
      if head_node:
        if head_node.dataval==newdata:
          prev.nextval=head_node.nextval
          
          
lis=SLinkList()
lis.headval=Node('aa')
ee=Node('bb')
lis.headval.nextval=ee

lis.head_insert('cc')
lis.tail_insert('dd')
lis.middle_insert(ee,"Fri")
lis.remove_node('bb')

lis.traversal_slist()