1 class Node(object):
 2     
 3     def __init__(self, value=None):
 4         self.value = value
 5         self.next, self.prev = None, None
 6 
 7 class Circular_Double_Linked_List(object):
 8     
 9     def __init__(self, maxsize=None):
10         self.root = Node()
#我習慣於從空的鏈表開始就是個循環鏈表
 
11         self.root.next = self.root
12         self.root.prev = self.root
13         self.count = 0
14         self.maxsize = maxsize
15     
16     def __len__(self):
17         return self.count
18     
19     def append(self, value):
#這裏的意思是如果maxsize不為None的前提下 len(self) >= self.maxsize
 
20         if self.maxsize is not None and len(self) >= self.maxsize:
21             raise Exception("Linked List Full")
22         node = Node(value)
23         tailnode = self.root.prev
24         tailnode.next = node
25         node.next = self.root
26         self.root.prev = node
27         node.prev = tailnode
 
28         self.count += 1
29     
30     def append_left(self, value):
31         if self.maxsize is not None and len(self) >= self.maxsize:
32             raise Exception("Linked List Full")
33         headnode = self.root.next
34         node = Node(value)
35         self.root.next = node
36         node.next = headnode
37         headnode.prev = node
38         node.prev = self.root
39         self.count += 1
40     
41     def iter_node(self):
42         curnode = self.root.next
43         while curnode is not self.root:
44             yield curnode
45             curnode = curnode.next
46     
47     def __iter__(self):
48         for node in self.iter_node():
49             yield node.value
50     
51     def find(self, value):
52         for index,node in enumerate(self.iter_node()):
53             if node.value == value:
54                 return index
55         return -1
56     
57     def remove(self, node):
58         if node is self.root:
59             raise Exception(‘remove empty Liked List‘)
60         prevnode = node.prev
61         nextnode = node.next
62         prevnode.next = nextnode
63         nextnode.prev = prevnode
64         value = node.value
65         del node
66         self.count -= 1
67         return value
#這裏也可以實現 O(1)操作的pop和popleft

def popleft(self):
        if self.root.next is self.root:
            raise Exception(‘pop from a empty linked list‘)
        headnode = self.root.next
        self.root.next = headnode.next
        headnode.next.prev = self.root
        value = headnode.value
        del headnode
        self.count -= 1
        return value

def pop(self):
        if self.root.next is self.root:
            raise Exception(‘pop from a empty linked list‘)
        tailnode = self.root.prev
        self.root.prev = tailnode.prev
        tailnode.prev.next = self.root
        value = tailnode.value
        del tailnode
        self.count -= 1
        return value

68     
69 if __name__ == "__main__":
70     cl = Circular_Double_Linked_List()
71     assert list(cl) == []
72     for i in range(5):
73         cl.append(i)
74     assert len(cl) == 5
75     assert list(cl) == [0, 1, 2, 3, 4]
76     assert cl.find(3) == 3
77     assert cl.find(5) == -1

python 實現循環雙端鏈表Circular_Double_Linked_List