python-实现双链表

　　双链表和单链表进行比较的优点与不同

1. 节点多了一个前驱指针域
2. 在很多基本操作上，多了一种选择，因为双链表可以向前进行移动寻位
3. 如果给每个节点添加一个对应的下标，那么在寻找节点时，我们可以使用二分发来进行节点的寻址工作，这相对于单链表是一个性能的优化

 7  """                      
  8  python实现双链表         
  9  """                      
 10 class Node(object):       
 11     def __init__(self,elem):
 12         self.elem = elem  
 13         self.next = None  
 14         self.front = None 
 15 class linklist(object):   
 16     def __init__(self,node = None):#链表的初始化
 17         self.__head = node
 18         self.curlen = 0   
 19     def empty(self):      
 20         if self.head == None:
 21             raise Exception("链表为空")
 22     def len(self):        
 23         return self.curlen
 24     def add_head(self,item):
 25         node = Node(item) 
 26         node.next = self.__head
 27         self.__head = node
 28         self.curlen += 1  
 29     def add_tail(self,item):
 30         node = Node(item) 
 31         tempnode = self.__head
 32         while tempnode != None:
 33             tempnode = tempnode.next
 34         tempnode.next = node
 35         self.curlen += 1  
 36     def insert(self,location,item):
 37         node = Node(item) 
 38         if location < 0 or location > self.curlen - 1:
 39             raise Exception("插入位置非法")
 40         elif location == 0:
 41             self.add_head(item)
 42         elif location == self.curlen:
 43             tempnode = self.__head
 44             while tempnode.next != None:
 45                 tempnode = tempnode.next
 46             tempnode.next = node
 47             self.curlen += 1
 48         else:             
 49             tempnode = self.__head
 50             for i in range(location - 1):
 51                 tempnode = tempnode.next
 52             node.next = tempnode.next
 53             tempnode.next = node
 54             self.curlen += 1
 55     def delitem(self,item):
 56         if self.__head.elem == item:
 57             self.__head = self.__head.next
 58         else:             
 59             tempnode = self.__head
 60                           
 61             while tempnode!= None:
 62                 if tempnode.next.elem == item:
 63                     break 
 64                 tempnode = tempnode.next
 65             tempnode.next = tempnode.next.next
 66     def change(self,item,changed_item):
 67         tempnode = self.__head
 68         while tempnode != None:
 69             if tempnode.elem == item:
 70                 tempnode.elem = changed_item
 71                 break     
 72     def search(self,item):
 73         tempnode = self.__head
 74         while tempnode != None:
 75             if tempnode.elem == item:
 76                 return True                      
77             tempnode = tempnode.next
 78         return False     
 79     def display(self):   
 80         tempnode = self.__head
 81         while tempnode != None:
 82             print(tempnode.elem,end = " ")
 83             tempnode = tempnode.next
 84         print()          
 85 if __name__ == "__main__":
 86     linklist1 = linklist()
 87     linklist1.add_head(1)
 88     linklist1.add_head(2)
 89     linklist1.insert(0,3)
 90     linklist1.display()  
 91     print(linklist1.curlen)
 92     linklist1.delitem(2)
 93     linklist1.display() 
 94     linklist1.change(3,4)
 95     print(linklist1.search(4))
 96     linklist1.display()               

此代码并没有充分的利用双链表的优点来进行操作，有兴趣的同学可以在此基础上来进行修改