Leetcode练习，将两个非负整数相加，整数一字符串的形式保存，逆向存储。要求得到的结果也是字符串。-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