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

解题思路:

   大体就是模拟整数相加的过程，需要注意的就是进位的情况.

解题代码:

/** * 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 NULL;        ListNode *head = NULL,*last = NULL;        int add = 0 , tmp = ( l1 ? l1->val : 0 ) + ( l2 ? l2->val : 0) ;        head = last = new ListNode(tmp%10);        if(l1)            l1 = l1->next;        if(l2)            l2 = l2->next;        add = tmp/10;        while(l1 && l2)        {            tmp = l1->val + l2->val + add;            add = tmp/10;            last->next = new ListNode(tmp%10);            last = last->next;            l1 = l1->next , l2 = l2->next;        }        while(l1)        {            tmp = l1->val + add;            add = tmp/10;            last->next = new ListNode(tmp%10);            last = last->next , l1 = l1->next;        }        while(l2)        {            tmp = l2->val + add ;            add = tmp/10;            last->next = new ListNode(tmp%10);            last = last->next , l2 = l2->next;        }        if(add)            last->next = new ListNode(add);        return head;    }};