题目：2. 两数相加 - 力扣（LeetCode）

代码：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """

        #计算l1和l2最长长度
        lenth = 0

        p1 = l1
        p2 = l2
        while(p1!=None or p2!=None):
            if p1 != None:
                p1 = p1.next
                
            if p2 != None:
                p2 = p2.next
            lenth += 1

        p = ListNode()
        head = ListNode()
        
        #保存下一次进位用
        jinWeiN = 0
        for i in range(lenth):
            #jinWei提取上次进位结果
            jinWei = jinWeiN
            temp = 0

            if(l1 == None):
                temp = l2.val
            elif(l2 == None):
                temp = l1.val
            else:
                temp = l1.val + l2.val
            temp += jinWei

            #判断下一位是否要进位
            if(temp >= 10):
                jinWeiN = 1
                temp -= 10
            else : jinWeiN = 0

            n1 = ListNode(temp)
            if i == 0:
                p = n1
                head = p
            else:
                p.next = n1
                p = n1

            if l1 != None:
                l1 = l1.next

            if l2 != None:
                l2 = l2.next
        
        #避免最后加到99+9出现结果为08类似的情况
        if jinWeiN != 0:
            n1 = ListNode(jinWeiN)
            p.next = n1

        return head

这一步可以写成

x = l1.val if l1 else 0
y = l2.val if l2 else 0
total = x + y + remainder