python - python中的循环链表

Question

我被困在Python中实现循环链​​表的add函数。我有一个头指针，它应该是对节点的引用，但每次我向列表中添加一些内容时，头总是 None 。这是我到目前为止的代码:

class CircleList():

    __slots__ = ('head', 'size')

    def __init__(self):
        self.head = None
        self.size = 0

    def __str__(self):
        result = "<"
        node = self.head
        count = self.size
        while count != 0:
            result = result + str(node.data)
            if count != 1:
                result = result + ", "
            node = node.next
            count -= 1
        result = result + ">"
        return result

    def add(self, element):
        head = self.head
        print(head)
        size = self.size
        if head == None:
            head = Node(element, None)
            head.next = head
        else:
            cursor = head
            while cursor.next != head:
                cursor = cursor.next
            temp = Node(element, head)
            cursor.next = temp
        size += 1


class Node():
    __slots__ = ('data','next')

    def __init__(self, data, next):
        self.data = data
        self.next = next

这是驱动程序:

stream = open('data.txt', 'r')

circlelist = CircleList()

for name in stream
    circlelist.add(name)

print(circlelist)

Answer 1

您只需将新节点分配给 add() 方法中的本地 head 变量，而不是实际的 CircleList 实例成员。

您可能想做类似的事情:

def add(self, element):
    head = self.head
    print(head)
    size = self.size
    if head is None:
        self.head = head = Node(element, None)  # Also set the instance member.
        head.next = head