Leetcode 2[medium]-- 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.
思路： 题意简单，无需多说，两个链表的相同位置的node的值相加，如果两者的和大于10，则要考虑进位问题。