2. Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order 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.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

Explanation: 342 + 465 = 807.

思路：添加一个进位标志，

代码：python3

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        dummy=cur=ListNode(0)
        carry=0
        while l1 or l2 or carry:
            if l1:
                carry += l1.val
                l1=l1.next
            if l2:
                carry += l2.val
                l2=l2.next
            cur.next=ListNode(carry%10)
            cur=cur.next
            carry//=10
        return dummy.next