题目
You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Follow up: What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
解题思路
讲两个链表存入栈中，每次pop两个栈顶元素求和，把进位创建到一个新的节点中，最后返回的时候，如果起始节点是0则返回next，1直接返回该节点
代码
class Solution:
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
s1 = []
s2 = []
while l1 is not None:
s1.append(l1.val)
l1 = l1.next
while l2 is not None:
s2.append(l2.val)
l2 = l2.next
tmp = 0
res = ListNode(0)
while len(s1) != 0 or len(s2) != 0:
if len(s1) != 0:
tmp += s1.pop()
if len(s2) != 0:
tmp += s2.pop()
res.val = tmp % 10
head = ListNode(tmp // 10)
head.next = res
res = head
tmp //= 10
return res.next if res.val == 0 else res
