题目描述：

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

题目大意：

给定两个链表分别代表两个非负整数。数位以倒序存储，并且每一个节点包含一位数字。将两个数字相加并以链表形式返回。

解题思路：

题目难度较低，主要考察链表操作和加法进位的基础知识。

Python代码：

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @return a ListNode
    def addTwoNumbers(self, l1, l2):
        head = ListNode(0)
        l = head
        carry = 0
        while l1 or l2 or carry:
            sum, carry = carry, 0
            if l1:
                sum += l1.val
                l1 = l1.next
            if l2:
                sum += l2.val
                l2 = l2.next
            if sum > 9:
                carry = 1
                sum -= 10
            l.next = ListNode(sum)
            l = l.next
        return head.next

 

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