循环链表代码进入无限循环

Question

我是这样定义循环链表的。

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__()

然后我将项目插入到我的列表中

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

我想要一个我的循环列表的字符串表示，但看起来__iter__() 正在无限循环。我可以正确定义我的迭代器，并获得正确的字符串表示吗？

Answer 1

我会分解步骤。

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 - 节点用于保存您的数据，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__ 需要初始化一个 empty 列表。这意味着根本没有节点。为方便起见，我将self.last 定义为非常 简化代码（注意，非常，否则您将遇到困难）。

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

对于insert_first，您需要注意列表为空时的极端情况和一般情况。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

您的__iter__ 方法也应该以实物形式回应。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]

---

完整代码清单

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__()