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

Subscribe to see which companies asked this question.
**题目大意:**342+465=807两个数相加，每个数都是以倒叙排列在链表中。
分析：链表的使用，如何向链表添加元素，以及进位的处理。
代码：

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {            val = x;            next = NULL; } * }; */class Solution {public:    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {        ListNode *answer = new ListNode(0);//新建一个头结点        ListNode *newone;//用来当作链表的指针用        newone = answer;        int sum = 0,temp = 0;        while(l1!=NULL && l2 != NULL)        {            sum = sum + l1->val + l2->val;            temp = sum %10;            sum = sum/10;            newone->next = new ListNode(temp);            newone = newone->next;            l1 = l1->next;            l2 = l2->next;        }        while(l1!=NULL)        {            sum = sum + l1->val;            temp = sum %10;            sum = sum/10;            newone->next = new ListNode(temp);            newone = newone->next;            l1 = l1->next;        }        while(l2 != NULL)        {            sum = sum + l2->val;            temp = sum %10;            sum = sum/10;            newone->next = new ListNode(temp);            newone = newone->next;            l2 = l2->next;        }        if(sum !=0 )        {            newone->next = new ListNode(sum);            newone = newone->next;        }        return answer->next;    }};

也有更为简单的写法，但目前就可以掌握这个，正在学习其他的写法，如有不对，敬请指教