2. Add Two Numbers

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

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* addTwoNumbers(ListNode* L1, ListNode* L2) {        ListNode res(0);        ListNode *tail = &res;        div_t sum = {0, 0};        while(sum.quot > 0 || L1 || L2){            if(L1){                sum.quot += L1->val;                L1 = L1->next;            }            if(L2){                sum.quot += L2->val;                L2 = L2->next;            }            sum = div(sum.quot, 10);            tail->next = new ListNode(sum.rem);//注意 这里不是头结点res， 而是变量tail->            tail = tail->next;        }        return res.next;//注意这里 不是 res->next;    }};