Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

 思路：新建一个新的链表，头指针指向一个0，但实际从头指针的下一个开始指向计算的结点，当l1，l2其中一个不为空或者carry位不为0，就进行计算，直到条件不成立。

/**
 * 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;
        ListNode *p=new ListNode(0);
        ListNode *q=p;
        while(l1||l2||carry)
        {
            if(l1)
            {
                carry+=l1->val;
                l1=l1->next;
            }
            if(l2)
            {
                carry+=l2->val;
                l2=l2->next;
            }
            p->next=new ListNode(carry%10);
            carry/=10;
            p=p->next;
        }
        return q->next;
    }
};