两数相加

给你两个 非空 的链表，表示两个非负的整数。它们每位数字都是按照 逆序 的方式存储的，并且每个节点只能存储 一位 数字。

请你将两个数相加，并以相同形式返回一个表示和的链表。

你可以假设除了数字 0 之外，这两个数都不会以 0 开头。

示例 1：

• 输入：l1 = [2,4,3], l2 = [5,6,4]
• 输出：[7,0,8]
• 解释：342 + 465 = 807.

示例 2：

• 输入：l1 = [0], l2 = [0]
• 输出：[0]

示例 3：

• 输入：l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
• 输出：[8,9,9,9,0,0,0,1]

示例代码：

# 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
        """
        count = 0
        ret = ListNode()
        tmp = ret
        while l1 or l2 or count:
            num = 0
            if l1:
                num += l1.val
                l1 = l1.next
            if l2:
                num += l2.val
                l2 = l2.next
            if count:
                num += count
                count -= 1
            count, num = divmod(num, 10)
            tmp.next = ListNode(num)
            tmp = tmp.next
        return ret.next
                

测试代码：

#  data structure
class LinkNode(object):
    def __init__(self, val):
        self.val = val
        self.next = None


#  create the LinkList
def create_link(link):
    if not link:
        return
    p = head = LinkNode(link[0])
    for i in link[1:]:
        p.next = LinkNode(i)
        p = p.next
    return head


#  print the link
def print_link(head):
    while head:
        print(head.val, end=' ')
        head = head.next
    print()


#  两数相加
class Add(object):
    def add(self, x, y):
        count = 0
        ret = tmp = LinkNode(None)
        while x or y or count:
            num = 0
            if x:
                num += x.val
                x = x.next
            if y:
                num += y.val
                y = y.next
            if count:
                num += count
                count -= 1
            count, num = divmod(num, 10)
            tmp.next = LinkNode(num)
            tmp = tmp.next
        return ret.next


l1 = [9, 2, 7]
l2 = [5, 9, 5]
obj1 = create_link(l1)
obj2 = create_link(l2)
print_link(obj1)
print_link(obj2)
obj = Add()
result = obj.add(obj1, obj2)
print_link(result)

运行结果：