/**

* 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) {

int carry = 0;

if(l1==NULL) return l2;

if(l2==NULL) return l1;

ListNode* h = l1;

ListNode* pre = l1;

while(l1!=NULL)

{

int l2val = l2?l2->val:0;

l1->val += l2val+carry;

carry = l1->val/10;

l1->val= l1->val%10;

pre = l1;

l1 = l1->next;

l2 = l2?l2->next:NULL;

if(l1 == NULL) {

pre->next = l2;

l2 = NULL;

l1 = pre->next;

}

}

if(carry!=0){

pre->next = new ListNode(1);

}

return h;

}

};