链表

链表的定义：

　　链表(linked list)是由一组被称为结点的数据元素组成的数据结构，每个结点都包含结点本身的信息和指向下一个结点的地址。由于每个结点都包含了可以链接起来的地址信息，所以用一个变量就能够访问整个结点序列。也就是说，结点包含两部分信息：一部分用于存储数据元素的值，称为信息域；另一部分用于存储下一个数据元素地址的指针，称为指针域。链表中的第一个结点的地址存储在一个单独的结点中，称为头结点或首结点。链表中的最后一个结点没有后继元素，其指针域为空。　　

如下图所示：

 

单链表的结构：

单链表的插入和删除示意图：

 

python实现代码：

#!/usr/bin/python# -*- coding: utf-8 -*-class Node(object):    def __init__(self,val,p=0):        self.data = val        self.next = pclass LinkList(object):    def __init__(self):        self.head = 0    def __getitem__(self, key):        if self.is_empty():            print 'linklist is empty.'            return        elif key <0  or key > self.getlength():            print 'the given key is error'            return        else:            return self.getitem(key)    def __setitem__(self, key, value):        if self.is_empty():            print 'linklist is empty.'            return        elif key <0  or key > self.getlength():            print 'the given key is error'            return        else:            self.delete(key)            return self.insert(key)    def initlist(self,data):        self.head = Node(data[0])        p = self.head        for i in data[1:]:            node = Node(i)            p.next = node            p = p.next    def getlength(self):        p =  self.head        length = 0        while p!=0:            length+=1            p = p.next        return length    def is_empty(self):        if self.getlength() ==0:            return True        else:            return False    def clear(self):        self.head = 0    def append(self,item):        q = Node(item)        if self.head ==0:            self.head = q        else:            p = self.head            while p.next!=0:                p = p.next            p.next = q    def getitem(self,index):        if self.is_empty():            print 'Linklist is empty.'            return        j = 0        p = self.head        while p.next!=0 and j <index:            p = p.next            j+=1        if j ==index:            return p.data        else:            print 'target is not exist!'    def insert(self,index,item):        if self.is_empty() or index<0 or index >self.getlength():            print 'Linklist is empty.'            return        if index ==0:            q = Node(item,self.head)            self.head = q        p = self.head        post  = self.head        j = 0        while p.next!=0 and j<index:            post = p            p = p.next            j+=1        if index ==j:            q = Node(item,p)            post.next = q            q.next = p    def delete(self,index):        if self.is_empty() or index<0 or index >self.getlength():            print 'Linklist is empty.'            return        if index ==0:            q = Node(item,self.head)            self.head = q        p = self.head        post  = self.head        j = 0        while p.next!=0 and j<index:            post = p            p = p.next            j+=1        if index ==j:            post.next = p.next    def index(self,value):        if self.is_empty():            print 'Linklist is empty.'            return        p = self.head        i = 0        while p.next!=0 and not p.data ==value:            p = p.next            i+=1        if p.data == value:            return i        else:            return -1l = LinkList()l.initlist([1,2,3,4,5])print l.getitem(4)l.append(6)print l.getitem(5)l.insert(4,40)print l.getitem(3)print l.getitem(4)print l.getitem(5)l.delete(5)print l.getitem(5)l.index(5)

结果：

5
6
4
40
5
6