浅谈Python单向链表的实现

链表由一系列不必在内存中相连的结构构成，这些对象按线性顺序排序。每个结构含有表元素和指向后继元素的指针。最后一个单元的指针指向NULL。为了方便链表的删除与插入操作，可以为链表添加一个表头。

删除操作可以通过修改一个指针来实现。

插入操作需要执行两次指针调整。

1. 单向链表的实现

1.1 node实现

每个Node分为两部分。一部分含有链表的元素，可以称为数据域；另一部分为一指针，指向下一个Node。

class Node():
  __slots__=['_item','_next']  #限定Node实例的属性
  def __init__(self,item):
    self._item=item
    self._next=None   #Node的指针部分默认指向None
  def getItem(self):
    return self._item
  def getNext(self):
    return self._next
  def setItem(self,newitem):
    self._item=newitem
  def setNext(self,newnext):
    self._next=newnext

1.2 SinglelinkedList的实现

class SingleLinkedList(): 
  def __init__(self):
    self._head=None  #初始化链表为空表
    self._size=0

1.3 检测链表是否为空

def isEmpty(self):
  return self._head==None 

1.4 add在链表前端添加元素

def add(self,item):
  temp=Node(item)
  temp.setNext(self._head)
  self._head=temp

1.5 append在链表尾部添加元素

def append(self,item):
  temp=Node(item)
  if self.isEmpty():
    self._head=temp  #若为空表，将添加的元素设为第一个元素
  else:
    current=self._head
    while current.getNext()!=None:
      current=current.getNext()  #遍历链表
    current.setNext(temp)  #此时current为链表最后的元素
  

1.6 search检索元素是否在链表中

def search(self,item):
  current=self._head
  founditem=False
  while current!=None and not founditem:
    if current.getItem()==item:
      founditem=True
    else:
      current=current.getNext()
  return founditem

1.7 index索引元素在链表中的位置

def index(self,item):
  current=self._head
  count=0
  found=None
  while current!=None and not found:
    count+=1
    if current.getItem()==item:
      found=True
    else:
      current=current.getNext()
  if found:
    return count
  else:
    raise ValueError,'%s is not in linkedlist'%item

1.8 remove删除链表中的某项元素

def remove(self,item):
  current=self._head
  pre=None
  while current!=None:
    if current.getItem()==item:
      if not pre:
        self._head=current.getNext()
      else:
        pre.setNext(current.getNext())
      break
    else:
      pre=current
      current=current.getNext()

1.9 insert链表中插入元素

def insert(self,pos,item):
  if pos<=1:
    self.add(item)
  elif pos>self.size():
    self.append(item)
  else:
    temp=Node(item)
    count=1
    pre=None
    current=self._head
    while count<pos:
      count+=1
      pre=current
      current=current.getNext()
    pre.setNext(temp)
    temp.setNext(current)

全部代码

class Node():
  __slots__=['_item','_next']
  def __init__(self,item):
    self._item=item
    self._next=None
  def getItem(self):
    return self._item
  def getNext(self):
    return self._next
  def setItem(self,newitem):
    self._item=newitem
  def setNext(self,newnext):
    self._next=newnext
     
class SingleLinkedList(): 
  def __init__(self):
    self._head=None #初始化为空链表
  def isEmpty(self):
    return self._head==None
  def size(self):
    current=self._head
    count=0
    while current!=None:
      count+=1
      current=current.getNext()
    return count
  def travel(self):
    current=self._head
    while current!=None:
      print current.getItem()
      current=current.getNext()
  def add(self,item):
    temp=Node(item)
    temp.setNext(self._head)
    self._head=temp
 
  def append(self,item):
    temp=Node(item)
    if self.isEmpty():
      self._head=temp  #若为空表，将添加的元素设为第一个元素
    else:
      current=self._head
      while current.getNext()!=None:
        current=current.getNext()  #遍历链表
      current.setNext(temp)  #此时current为链表最后的元素
  def search(self,item):
    current=self._head
    founditem=False
    while current!=None and not founditem:
      if current.getItem()==item:
        founditem=True
      else:
        current=current.getNext()
    return founditem
  def index(self,item):
    current=self._head
    count=0
    found=None
    while current!=None and not found:
      count+=1
      if current.getItem()==item:
        found=True
      else:
        current=current.getNext()
    if found:
      return count
    else:
      raise ValueError,'%s is not in linkedlist'%item       
  def remove(self,item):
    current=self._head
    pre=None
    while current!=None:
      if current.getItem()==item:
        if not pre:
          self._head=current.getNext()
        else:
          pre.setNext(current.getNext())
        break
      else:
        pre=current
        current=current.getNext()           
  def insert(self,pos,item):
    if pos<=1:
      self.add(item)
    elif pos>self.size():
      self.append(item)
    else:
      temp=Node(item)
      count=1
      pre=None
      current=self._head
      while count<pos:
        count+=1
        pre=current
        current=current.getNext()
      pre.setNext(temp)
      temp.setNext(current)
 
if __name__=='__main__':
  a=SingleLinkedList()
  for i in range(1,10):
    a.append(i)
  print a.size()
  a.travel()
  print a.search(6)
  print a.index(5)
  a.remove(4)
  a.travel()
  a.insert(4,100)
  a.travel()