python - 循环链表代码陷入无限循环

Question

我已经这样定义了循环链表。

class Link(object):
    def __init__ (self, data, next = None):
        self.data = data
        self.next = next


class CircularList(object):

    def __init__ ( self ):
        self.first = Link(None, None)
        self.first.next = self.first

    def insert_first ( self, item ):
        new_link = Link(item)
        new_link.next = self.first
        self.first = new_link

    def __iter__(self):
        current = self.first
        first = current
        while current.next != first:
            yield current
            current = current.next

    def __str__(self):
        return str([Link.data for Link in self])

    def __repr__(self):
        return self.__str__()

然后我将项目插入我的列表

a = CircularList()
a.insert_first(4)
a.insert_first(5)

我想要循环列表的字符串表示形式，但看起来 __iter__() 正在无限循环。我可以正确定义迭代器，并获得正确的字符串表示形式吗？

Answer 1

我将分解步骤。

首先，我将 Link 重命名为 Node。

class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

链接与节点不同 - 节点保存数据，链接将两个节点连接在一起。

接下来，CircularList 类需要进行一些更改。

__init__ 将需要初始化一个空列表。这意味着根本没有节点。为了方便起见，我定义了 self.last 来极大地简化代码(注意，极大，你将会遇到困难否则)。

class CircularList(object):
    def __init__(self):
        self.first = self.last = None

对于insert_first，您需要处理列表为空时的特殊情况以及一般情况。相应地更新 self.first 和 self.last。

def insert_first(self, item):
    if self.first is None:
        self.first = self.last = Node(item)
        self.first.next = self.first
    else:
        self.first = Node(item, self.first)
        self.last.next = self.first

你的__iter__方法也应该以同样的方式响应。内嵌评论。

def __iter__(self):
    # corner case - yield empty list
    if not self.first:
        yield []
    else:
        # start by yielding the head node
        yield self.first
        cur = self.first.next
        # iterate as long as you do not see the head node again 
        while cur is not self.first:
            yield cur
            cur = cur.next

其他方法保持不变。测试代码:

a = CircularList()
for i in [5, 4, 3, 2, 1]:
    a.insert_first(i)

print(a)
[1, 2, 3, 4, 5]

<小时/>

完整代码列表

class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

class CircularList(object):
    def __init__(self):
        self.first = self.last = None

    def insert_first(self, item):
        if self.first is None:
            self.first = self.last = Node(item)
            self.first.next = self.first    
        else:
            self.first = Node(item, self.first)
            self.last.next = self.first

    def __iter__(self):
        if not self.first:
            yield []
        else:
            yield self.first
            cur = self.first.next
            while cur is not self.first:
                yield cur
                cur = cur.next

    def __str__(self):
        return str([Link.data for Link in self])

    def __repr__(self):
        return self.__str__()