输入：[2,4,3] [5,6,4]

输出：[7,0,8]

过程：342+456=807 7->0->8

解法：无非就是两个链表相加，生成新链表而已，只要遍历链表按照十进制加法运算就行了，注意一下进位保存到一下节点。

代码：

ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* head = NULL;
        ListNode* node = NULL;
        ListNode* tail = NULL;
        ListNode *t1 = l1;
        ListNode *t2 = l2;
        int jinwei = 0;
        int sum;
        for (; t1 || t2 || jinwei; )
        {
            int num1 = 0;
            if (t1)
            {
                num1 = t1->val;
                t1 = t1->next;
            }
            int num2 = 0;
            if (t2)
            {
                num2 = t2->val;
                t2 = t2->next;
            }
            sum = num1 + num2 + jinwei;
            if (sum >= 10) {
                sum -= 10;
                jinwei = 1;
            }
            else
                jinwei = 0;

            //尾插法
            node = (ListNode*)malloc(sizeof(ListNode));
            node->val = sum;
            node->next = NULL;

            if (head == NULL)
            {
                head = node;
                tail = node;
            }
            else
            {
                tail->next = node;
                tail = node;
            }
        }
        return head;
    }