leetcode: Add Tow Numbers

You are given two linked lists representing two non-negative numbers. 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.

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

这个写法更简洁，新开个数组，而不是原地

/** * 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 == NULL)            return l2;        if( l2 == NULL)            return l1;        int carry = 0;        ListNode *l3 = NULL;        ListNode *p = l3;        while( l1 || l2){            int sum = carry;            if( l1){                sum += l1->val;                l1 = l1->next;            }            if( l2){                sum += l2->val;                l2 = l2->next;            }            carry = sum / 10;            sum = sum % 10;                        ListNode * tmp = new ListNode(sum);            if( !l3){                l3 = tmp;                p = l3;            }            else{                p->next = tmp;                p = p->next;            }        }        if( carry){            ListNode *tmp = new ListNode(carry);            p->next = tmp;        }        return l3;    }};