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(),end=' ')
            current = current.getNext()
        print()

    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()

 输出：

9
1 2 3 4 5 6 7 8 9
True
5
1 2 3 5 6 7 8 9
1 2 3 100 5 6 7 8 9