[LeetCode_2] Add Two Numbers

LeetCode: 2. 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 )
    {
        int carry = 0;// 是否需要进位
        ListNode * tail = new ListNode(0);
        ListNode * ptr = tail;// 当前指针
        
        while(l1 != NULL || l2 != NULL){
            int val1 = 0,val2 = 0;
            if (l1 != NULL){
                val1 = l1 -> val;
                l1 = l1 -> next;
            }
            if (l2 != NULL){
                val2 = l2 -> val;
                l2 = l2 -> next;
            }
            ptr -> val = (val1 + val2 + carry) % 10 ;
            carry = ( val1 + val2 + carry )/ 10;
            // 增加        
            if (l1 != NULL || l2 != NULL){
                ptr -> next = new ListNode(0);
                ptr = ptr -> next;
            }
        }
        if (carry == 1){
                ptr -> next = new ListNode(1);
        }
        return tail;
    }

};