4.用链表实现两个大数相加

/**
* 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 *p = l1, *q = l2;
ListNode *head = new ListNode(0);
ListNode *h = head;
int flag = 0;
while (p != NULL || q != NULL)
{
ListNode *newNode = new ListNode(((p != NULL ? p->val : 0) + (q != NULL ? q->val : 0) + flag) % 10);
flag = ((p != NULL ? p->val : 0) + (q != NULL ? q->val : 0) + flag) / 10;
h->next = newNode;
h = h->next;
if (p != NULL) p = p->next;
if (q != NULL) q = q->next;
}
if (flag)
{
ListNode *newNode = new ListNode(flag);
h->next = newNode;
}
return head->next;
}
};