Leetcode2.Add Two Numbers两数相加

给定两个非空链表来表示两个非负整数。位数按照逆序方式存储，它们的每个节点只存储单个数字。将两数相加返回一个新的链表。

你可以假设除了数字 0 之外，这两个数字都不会以零开头。

示例：

输入：(2 -> 4 -> 3) + (5 -> 6 -> 4) 输出：7 -> 0 -> 8 原因：342 + 465 = 807

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2)
    {
        int x = 0;
        ListNode* head = NULL;
        ListNode* last = NULL;
        while(l1 && l2)
        {
            int temp = l1 ->val + l2 ->val + x;
            x = temp / 10;
            temp = temp % 10;
            if(head == NULL)
            {
                head = new ListNode(temp);
                last = head;
            }
            else
            {
                last ->next = new ListNode(temp);
                last = last ->next;
            }
            l1 = l1 ->next;
            l2 = l2 ->next;
        }
        while(l1)
        {
            int temp = l1 ->val + x;
            x = temp / 10;
            temp = temp % 10;
            if(head == NULL)
            {
                head = new ListNode(temp);
                last = head;
            }
            else
            {
                last ->next = new ListNode(temp);
                last = last ->next;
            }
            l1 = l1 ->next;
        }
        while(l2)
        {
            int temp = l2 ->val + x;
            x = temp / 10;
            temp = temp % 10;
            if(head == NULL)
            {
                head = new ListNode(temp);
                last = head;
            }
            else
            {
                last ->next = new ListNode(temp);
                last = last ->next;
            }
            l2 = l2 ->next;
        }
        if(x != 0)
        {
            last ->next = new ListNode(x);
            last = last ->next;
        }
        return head;
    }
};