leetcode练习 Add Two Numbers

/**
* 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) {
if (l1 == NULL) return l2;
if (l2 == NULL) return l1;
ListNode* result = new ListNode(0);
ListNode* tail = new ListNode(0);
int flag = 0;
result->next = tail;
tail->val = (l1->val+l2->val)%10;
if ((l1->val+l2->val) >= 10) {
flag = 1;
} else {
flag = 0;
}
ListNode* temp1 = l1->next;
ListNode* temp2 = l2->next;
while (temp1 != NULL && temp2 != NULL) {
ListNode* n = new ListNode((temp1->val+temp2->val+flag)%10);
tail->next = n;
tail = n;
if ((temp1->val+temp2->val+flag) >= 10) {
flag = 1;
} else {
flag = 0;
}
temp1 = temp1->next;
temp2 = temp2->next;
}
if (!temp1) {
while (temp2) {
ListNode* n = new ListNode((temp2->val+flag)%10);
if ((temp2->val+flag) >= 10) {
flag = 1;
} else {
flag = 0;
}
tail->next = n;
tail = n;
temp2 = temp2->next;
}
}
else if (!temp2) {
while (temp1) {
ListNode* n = new ListNode((temp1->val+flag)%10);
if ((temp1->val+flag) >= 10) {
flag = 1;
} else {
flag = 0;
}
tail->next = n;
tail = n;
temp1 = temp1->next;
}
}
if (flag) {
ListNode* f = new ListNode(flag);
tail->next = f;
tail = f;
}
result = result->next;
return result;
}
};