Leetcode 2. Add Two Numbers（python）

链表操作 需要维护一个进位

# 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):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        carry=0
        root=last=ListNode(0)
        while l1 or l2 or carry:
            val1=val2=0
            if l1:
                val1=l1.val
                l1=l1.next
            if l2:
                val2=l2.val
                l2=l2.next
            carry,val=divmod(val1+val2+carry,10)
            last.next=ListNode(val)
            last=last.next
        return root.next