leetCode练习（2）

题目：Add Two Numbers           

难度：medium         

问题描述：

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

错误点：分别计算出l1和l2代表的int值再相加，这是错误解法，因为int会溢出。

解题思路：每位相加注意进位即可。代码如下：