链接：https://leetcode.com/problems/add-two-numbers/
原题：
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

分析:
这道题实际上就是倒叙的链表，最终算出和，并以链接的形式呈现。
还是循环，但要注意可能有进1位 以及 两个数字长度不同的问题

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        ListNode l1tmp = l1;
        ListNode l2tmp = l2;
        int add1 = 0;
        while (true) {
            int l1num = l1tmp.val;
            int l2num = l2tmp ==null?0:l2tmp.val;
            int value = l1num + l2num + add1;
            add1 = value / 10;
            value = value % 10;
            l1tmp.val = value;
            if (l1tmp.next == null) {
                if((l2tmp!=null &&  l2tmp.next!=null)|| add1!=0) {
                    l1tmp.next = new ListNode(0);
                } else {
                    break;
                }
            }
            l1tmp = l1tmp.next;
            l2tmp = l2tmp == null?null:l2tmp.next;
        }
        return l1;
    }

代码效率没有很高，待优化