Python Leetcode在列表节点中添加两个sum'；未定义错误

2#@返回一个ListNode 3个def addtwo编号（self、l1、l2）： ---->4虚拟=cur=列表节点（0） 5进位=0 6当l1或l2或运载时：

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NameError:名称“ListNode”未定义

ListNode应由LeetCode定义，ListNode由LeetCode定义的Playerd按钮中有调试代码

最初在编辑器面板中提供，如Python2所示：

class Solution:
# @return a ListNode
    def addTwoNumbers(self, l1, l2):
        dummy = cur = ListNode(0)
        carry = 0
        while l1 or l2 or carry:
            if l1:
                carry += l1.val
                l1 = l1.next
            if l2:
                carry += l2.val
                l2 = l2.next
            cur.next = ListNode(carry%10)
            cur = cur.next
            carry //= 10
        return dummy.next

l1 = [203] # Array of numbers
l2 = [433]
s = Solution()
print(s.addTwoNumbers(l1, l2)) 

下面是在Python中使用while循环的完整解决方案，但是，使用递归调用要好得多：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

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嗯，您还没有在任何地方定义

ListNode

类，所以。。。为什么您希望这段代码能工作？您能编写ListNode类吗？对于那些不使用Leetcode的人来说，它会派上用场。我的答案中提供了ListNode。

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2, carry = 0):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        # Initialize the tmp result and the returned result
        head_result = tmp_result = ListNode(0)
        # While loop until there are neither nodes or carries left
        while l1 != None or l2 != None or carry > 0:
            # Store the values of the linked lists into variables, and set zero if no more nodes
            x = (l1.val if l1 != None else 0)
            y = (l2.val if l2 != None else 0)
            # Calculate the sum
            sum_res = x + y + carry
            # Make the tens of the sum be the carry
            carry = sum_res // 10
            # Store the units of the sum in the result's next node
            tmp_result.next = ListNode(sum_res % 10)
            # Traverse to the next result's node
            tmp_result = tmp_result.next
            # Traverse to the next nodes in the linked lists
            l1 = (l1.next if l1 else None)
            l2 = (l2.next if l2 else None)
        # Make sure no carries are left
        if carry > 0: tmp_result.next = ListNode(carry)
        # Set the head of the result to skip the zero intialization, if there's something in the next node
        if head_result.next != None: head_result = head_result.next
        return head_result