数据结构-链表

# 数据结构包括链表、栈、队列和二叉树

# python基本的数据类型也有数据结构的影子，如列表、元组和字典

# 自引用类包含一个指向相同类的对象的成员

# 如Node类拥有两个成员—成员数据和指向一个Node对象的引用成员nextNode

# None引用一般表示数据结构的末尾

3个自引用类的链接对象

# 链表：通过引用链接相连的称为节点的自引用类的线性集合
# 通过指向链表头节点的引用访问
# 可以在链表的任何位置进行插入和删除操作
# 单向环链表：最后一个节点包含指向头结点的引用
# 双向链表允许前后遍历操作

ListModule.py实现了链表类List

  1 # ListModule.py
  2 # Classes List and Node definitions.
  3 
  4 class Node:
  5    """Single node in a data structure"""
  6 
  7    def __init__( self, data ):
  8       """Node constructor"""
  9       
 10       self._data = data
 11       self._nextNode = None
 12     
 13    def __str__( self ):
 14       """Node data representation"""
 15 
 16       return str( self._data )      
 17 
 18 class List:
 19    """Linked list"""
 20 
 21    def __init__( self ):
 22       """List constructor"""
 23 
 24       self._firstNode = None
 25       self._lastNode = None
 26 
 27    def __str__( self ):
 28       """List string representation"""
 29 
 30       if self.isEmpty():
 31          return "empty"
 32 
 33       currentNode = self._firstNode
 34       output = []
 35 
 36       while currentNode is not None:
 37          output.append( str( currentNode._data ) )
 38          currentNode = currentNode._nextNode
 39 
 40       return " ".join( output )      
 41 
 42    def insertAtFront( self, value ):
 43       """Insert node at front of list"""
 44 
 45       newNode = Node( value )
 46 
 47       if self.isEmpty():  # List is empty
 48          self._firstNode = self._lastNode = newNode
 49       else:   # List is not empty
 50          newNode._nextNode = self._firstNode
 51          self._firstNode = newNode
 52         
 53    def insertAtBack( self, value ):
 54       """Insert node at back of list"""
 55 
 56       newNode = Node( value )
 57 
 58       if self.isEmpty():  # List is empty
 59          self._firstNode = self._lastNode = newNode
 60       else:  # List is not empty
 61          self._lastNode._nextNode =  newNode
 62          self._lastNode = newNode
 63 
 64    def removeFromFront( self ):
 65       """Delete node from front of list"""
 66 
 67       if self.isEmpty():  # raise exception on empty list
 68          raise IndexError, "remove from empty list"
 69 
 70       tempNode = self._firstNode
 71 
 72       if self._firstNode is self._lastNode:  # one node in list
 73          self._firstNode = self._lastNode = None
 74       else:
 75          self._firstNode = self._firstNode._nextNode
 76 
 77       return tempNode
 78 
 79    def removeFromBack( self ):
 80       """Delete node from back of list"""
 81 
 82       if self.isEmpty():  # raise exception on empty list
 83          raise IndexError, "remove from empty list"
 84      
 85       tempNode = self._lastNode
 86 
 87       if self._firstNode is self._lastNode:  # one node in list
 88          self._firstNode = self._lastNode = None
 89       else:
 90          currentNode = self._firstNode
 91 
 92          # locate second-to-last node
 93          while currentNode._nextNode is not self._lastNode:
 94                currentNode = currentNode._nextNode
 95                
 96          currentNode._nextNode = None
 97          self._lastNode = currentNode
 98 
 99       return tempNode
100     
101    def isEmpty( self ):
102       """Returns true if List is empty"""
103 
104       return self._firstNode is None

测试List类

 1 # -*- coding: utf-8 -*-
 2 """
 3 Created on Thu Aug 07 23:20:31 2014
 4 
 5 @author: Administrator
 6 """
 7 
 8 # Driver to test class List
 9 
10 from ListModule import List
11 
12 # instructions for user
13 instructions = """Enter one of the following:
14     1 to insert at beginning of list
15     2 to insert at end of list
16     3 to delete from beginning of list
17     4 to delete from end of list
18     5 to end list processing
"""
19 
20 # 创建空的List对象    
21 listObj = List()
22 
23 print instructions
24 
25 # obtain user choice until user chooses to quit ( choice 5 )
26 while 1:
27     choice = raw_input("Enter value:")
28     
29     # insert at front
30     if choice == "1":
31         listObj.insertAtFront(raw_input("Enter value:"))
32         print "The list is:",listObj
33     # insert at end
34     elif choice == "2":
35         listObj.insertAtBack(raw_input("Enter value:"))
36         print "The list is:", listObj
37     # delete from front
38     elif choice == "3":
39         try:
40             value = listObj.removeFromFront()
41         except IndexError, message:
42             print "Fail to remove: ",message
43         else:
44             print value, "removed from list"
45             print "The list is:",listObj
46     # delete from end
47     elif choice == "4":
48         try:
49             value = listObj.removeFromBack()
50         except IndexError, message:
51             print "Fail to remove:",message
52         else:
53             print value,"removed from list"
54             print "The list is:",listObj
55     # exit
56     elif choice == "5":
57         break   # terminate while loop
58     
59     # invalid choice
60     else:
61         print "Invalid choice:", choice
62         print instructions
63         
64 print "End list test
"

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