leetcode_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) {
        ListNode* res = new ListNode(-1);
        ListNode* cur = res;
        int carry = 0;
        while(l1 != NULL || l2 != NULL)
        {
            int n1 = l1==NULL?0:l1->val;
            int n2 = l2 == NULL ? 0 : l2->val;
            int sum = n1+n2+carry;
            carry = sum / 10;
            sum = sum % 10;
            ListNode *new_node = new ListNode(sum);
            cur->next = new_node;
            cur = new_node;
            if(l1 != NULL) l1 = l1->next;
            if(l2 != NULL) l2 = l2->next;
        }
        if(carry>0)
        {
            ListNode *new_node = new ListNode(carry);
            cur->next = new_node;            
        }
        return res->next;
    }
};