题2描述：
| 2 | Add Two Numbers | 29.10% | Medium |
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.
Example:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.C语言解法：
/*** Definition for singly-linked list.* struct ListNode {* int val;* struct ListNode *next;* };*/struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {struct ListNode *new = (struct ListNode*)malloc(sizeof(struct ListNode));struct ListNode *head = new;int carry = 0;while(l1!=NULL || l2 !=NULL){int d1 = (l1 == NULL) ? 0 :l1->val;int d2 = (l2 == NULL) ? 0 :l2->val;int sum = d1 + d2 + carry;int mod = sum % 10;carry = sum / 10;head->val = mod;if(l1!= NULL)l1 = l1->next;if(l2!= NULL)l2 = l2->next;if(l1 != NULL || l2 != NULL){head->next = (struct ListNode*)malloc(sizeof(struct ListNode));head = head->next;}}head->next = NULL;if(carry==1){head->next = (struct ListNode*)malloc(sizeof(struct ListNode));head->next->val = carry;head->next->next = NULL;}return new;}
