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.

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

需要考虑以下特殊情况：
【5】+ 【5】-> 【0，1】
【9，9】+ 【1】 -> 【0，0，1】

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     struct ListNode *next; * }; */struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {    struct ListNode *head = (struct ListNode *)malloc(sizeof(struct ListNode));    struct ListNode *curr = head;    struct ListNode *temp = NULL;    int carry = 0;//进位    while(l1 != NULL || l2 != NULL || carry != 0)    {        int x = (l1 != NULL) ? l1->val : 0;        int y = (l2 != NULL) ? l2->val : 0;        int sum = carry + x + y;        carry = sum/10;        temp = (struct ListNode *)malloc(sizeof(struct ListNode));        temp->val = sum%10;        temp->next = NULL;        //尾插法        curr->next = temp;        curr = temp;        if(l1 != NULL)            l1 = l1->next;        if(l2 != NULL)            l2 = l2->next;    }    return head->next;}