给定两个非空链表来表示两个非负整数。位数按照逆序方式存储，它们的每个节点只存储单个数字。将两数相加返回一个新的链表。
你可以假设除了数字 0 之外，这两个数字都不会以零开头。
示例：
输入：(2 -> 4 -> 3) + (5 -> 6 -> 4) 输出：7 -> 0 -> 8 原因：342 + 465 = 807
1 # Definition for singly-linked list. 2 # class ListNode(object): 3 # def __init__(self, x): 4 # self.val = x 5 # self.next = None 6 7 class Solution(object): 8 def addTwoNumbers(self, l1, l2): 9 """ 10 :type l1: ListNode 11 :type l2: ListNode 12 :rtype: ListNode 13 """ 14 if l1 == None: return l2 15 if l2 == None: return l1 16 // 使用dummyHead指向头结点，最后返回dummyHead.next 17 dummy_head = ListNode(0) 18 // 指针 19 pt = dummy_head 20 // 是否进位 21 carry = 0 22 while l1 and l2: 23 pt.next = ListNode((l1.val + l2.val + carry) % 10) 24 carry = (l1.val + l2.val + carry) / 10 25 pt = pt.next; 26 l1 = l1.next; 27 l2 = l2.next 28 if l1: 29 while l1: 30 pt.next = ListNode((l1.val + carry) % 10) 31 carry = (l1.val + carry) / 10 32 pt = pt.next; 33 l1 = l1.next 34 if carry == 1: 35 pt.next = ListNode(1) 36 return dummy_head.next 37 if l2: 38 while l2: 39 pt.next = ListNode((l2.val + carry) % 10) 40 carry = (l2.val + carry) / 10 41 pt = pt.next; 42 l2 = l2.next 43 if carry == 1: 44 pt.next = ListNode(1) 45 return dummy_head.next 46 if carry == 1: 47 pt.next = ListNode(1) 48 return dummy_head.next