Leetcode||2. Add Two Numbers

用一个变量记录进位。

//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) {
        ListNode *p1=l1,*p2=l2,*head=new ListNode(0),*p=head;

        int carry=0;
        while(p1||p2)
        {
            int val1=0,val2=0;
            if(p1)
            {
                val1=p1->val;
                p1=p1->next;
            }
            if(p2)
            {
                val2=p2->val;
                p2=p2->next;
            }
            int tmp=carry+val1+val2;
            p->next=new ListNode(tmp%10);
            carry=tmp/10;
            p=p->next;
        }
        if(carry!=0)
        {
            p->next=new ListNode(carry);
        }
        return head->next;
    }
};