两数相加

/**
 * 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&&!l2)
            return nullptr;
        else if(!l1||!l2)
            return (!l1)?l2:l1;
        
        int carry=0;
        ListNode *res=new ListNode(-1);
        ListNode *t1=l1,*t2=l2,*t=res;
        while(t1||t2||carry)
        {
            int num=0;
            if(t1)
                num+=t1->val;
            if(t2)
                num+=t2->val;
            num+=carry;
            
            t->next=new ListNode(num%10);
            carry=num/10;
            
            t=t->next;
            t1=t1?t1->next:nullptr;
            t2=t2?t2->next:nullptr;
        }
        ListNode *res1=res->next;
        res->next=nullptr;
        delete res;
        return res1;
    }
};