第七节 双向链表简单介绍和python代码实现

　　双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。一般我们都构造双向循环链表。

　

  1 class Node():
  2     '''节点类'''
  3     def __init__(self, elem):
  4         '''节点的两个参数，本身值elem以及指向下一个节点的地址next'''
  5         self.elem = elem
  6         self.next = None
  7         self.prev = None
  8 
  9 
 10 class DoubleLinkList():
 11     '''双链表'''
 12     def __init__(self, node = None):
 13         self.__head = None
 14 
 15     def sing_append(self, elem):
 16         '''链表尾部添加元素'''
 17         node = Node(elem)
 18         if self.is_empty():
 19             self.__head = node
 20         else:
 21             cur = self.__head
 22             while cur.next != None:
 23                 cur = cur.next
 24             cur.next = node
 25             node.prev = cur
 26 
 27     def is_empty(self):
 28         '''判断链表是否为空，第一次传入数据以后self.__head将永远指向node1对象'''
 29         return self.__head is None
 30 
 31     def sing_length(self):
 32         '''链表长度'''
 33         cur = self.__head
 34         # 将第一个元素的node实例赋值给cur，
 35         count = 0
 36         while cur != None:
 37             count+=1
 38             cur = cur.next
 39         return count
 40 
 41     def sing_travel(self):
 42         '''遍历整个列表'''
 43         cur = self.__head
 44         # 即将node1对象赋值给cur
 45         while cur != None:
 46             print(cur.elem)
 47             cur = cur.next
 48 
 49     def sing_add(self, item):
 50         node = Node(item)
 51         node.next = self.__head
 52         self.__head = node
 53         node.next.prev = node
 54 
 55     def sint_insert(self, pos, item):
 56         if pos <= 0:
 57             self.sing_add(item)
 58         elif pos > self.sing_length()-1:
 59             self.sing_append(item)
 60         else:
 61             cur = self.__head
 62             count = 0
 63             while count < pos:
 64                 count += 1
 65                 cur = cur.next
 66             node = Node(item)
 67             node.next = cur
 68             node.prev = cur.prev
 69             cur.prev.next = node
 70             cur.prev = node
 71 
 72     def sing_search(self,item):
 73         cur = self.__head
 74         while cur != None:
 75             cur = cur.next
 76             if item == cur.elem:
 77                 return True
 78             return False
 79 
 80     def sing_remove(self, item):
 81         cur = self.__head
 82         while cur != None:
 83             if item == cur.elem:
 84                 if cur == self.__head:
 85                     self.__head = cur.next
 86                     if cur.next:
 87                         # 判断链表是否只有一个节点
 88                         cur.next.prev = self.__head
 89                     break
 90                 else:
 91                     cur.prev.next = cur.next
 92                     if cur.next:
 93                         cur.next.prev = cur.prev
 94                     break
 95             else:
 96                 cur = cur.next
 97 
 98 if __name__ == "__main__":
 99     ll = DoubleLinkList()
100     ll.sing_append(1)
101     ll.sing_append(2)
102     # ll.sing_add(8)
103     ll.sing_append(3)
104     ll.sint_insert(-1,5)
105     ll.sing_travel()
106     print(ll.sing_search(5))
107     ll.sing_remove(3)
108     ll.sing_travel()