leetcode Add Two Numbers 链表加法

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

http://www.cnblogs.com/grandyang/p/4129891.html