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.

要注意的是两个链表可能不一样长度。

还有不能还原成数字，因为不知道链表的长度，可能链表的长度很大，超过了int的范围，或者超过了double的范围。

只能一位一位的变化。

代码是抄的LeetCode的代码。

自己没有写出来。

public static ListNode addTwoNumbers(ListNode l1, ListNode l2){        ListNode dummyHead = new ListNode(0);        ListNode p = l1, q = l2, curr = dummyHead;        int carry = 0;        while (p != null || q != null) {            int x = (p != null) ? p.val : 0;            int y = (q != null) ? q.val : 0;            int sum = carry + x + y;            carry = sum / 10;            curr.next = new ListNode(sum % 10);            curr = curr.next;            if (p != null) p = p.next;            if (q != null) q = q.next;        }        if (carry > 0) {            curr.next = new ListNode(carry);        }        return dummyHead.next;    }