LeetCode:Add Two 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

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;
    }
};