letCode-2

/**
 * 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 * result = new ListNode(0);
        int carry = 0;
        ListNode* curr = result;
        //有进位，任意链表均有值
        while(l1!=NULL || l2 != NULL | carry!=0){
　　　　　　　//这里分开判断
            if (l1 != NULL){
                carry += l1->val;
                l1 = l1->next;
            }
            if(l2 != NULL){
                carry += l2->val;
                l2 = l2->next;
            }
            ListNode* node = new ListNode(carry%10);
            //向下取整
            carry/=10;
            curr->next = node;
            curr = node;
        }
        return result;
    }
};