题目：

题解：

struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {struct ListNode *head = NULL, *tail = NULL;int carry = 0;while (l1 || l2) {int n1 = l1 ? l1->val : 0;int n2 = l2 ? l2->val : 0;int sum = n1 + n2 + carry;if (!head) {head = tail = malloc(sizeof(struct ListNode));tail->val = sum % 10;tail->next = NULL;} else {tail->next = malloc(sizeof(struct ListNode));tail->next->val = sum % 10;tail = tail->next;tail->next = NULL;}carry = sum / 10;if (l1) {l1 = l1->next;}if (l2) {l2 = l2->next;}}if (carry > 0) {tail->next = malloc(sizeof(struct ListNode));tail->next->val = carry;tail->next->next = NULL;}return head;
}