领扣中等版--两数相加（Add Two Numbers）

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

Python3:

# 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
        """
        num1 = ''
        num2 = ''
        while l1:
            num1 += str(l1.val)
            l1 = l1.next
        while l2:
            num2 += str(l2.val)
            l2 = l2.next
            
        num3 = int(num1[::-1]) + int(num2[::-1])
        l3_head = None
        tmp = None
        str_num3 = str(num3)[::-1]
        return [int(x) for x in str_num3]
        # for num in str_num3:
        #     l3 = ListNode(int(num))
        #     if tmp is not None:
        #         tmp.next = l3
        #     tmp = l3
        #     if num == str_num3[0]:
        #         l3_head = l3
        # return l3_head
l1 = ListNode(2)
l11 = ListNode(4)
l12 = ListNode(3)
l1.next = l11  
l11.next = l12
                          
                          
l2 = ListNode(5)
l21 = ListNode(6)
l22 = ListNode(4)
l2.next = l21  
l21.next = l22
    
solution = Solution()
l3 = solution.addTwoNumbers(l1, l2)
return_list = []
# tmp_l3 = l3
# while tmp_l3:
#     return_list.append(tmp_l3.val)
#     tmp_l3 = tmp_l3.next
print(l3)