LeetCode # Array # 2-Add Two Numbers

题目：

     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.

Example：

 Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
 Output: 7 -> 0 -> 8
 Explanation: 342 + 465 = 807.

解答：
 由于自己写的比较捉急，所以参考了高赞答案：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode prev = new ListNode(0);
        ListNode head = prev;
        int carry = 0;
        while (l1 != null || l2 != null || carry != 0) {//符合条件的进入循环
             ListNode cur = new ListNode(0);
             int sum = ((l2 == null) ? 0 : l2.val )+ ((l1 == null) ? 0 : l1.val) + carry;//加出当前的和；
             cur.val = sum %10;//将个位数赋值
             carry = sum / 10 ;//将十位数赋值
             prev.next = cur;//将cur保存在prev。next；
             prev = cur;
             
             l1= (l1 == null )? l1 : l1.next;//两个数向后推。
             l2 = (l2 == null)? l2 : l2.next;
            
        }
        return head.next;
    }
}

 代码中，需要明白的是：java中对于类型的引用和赋值过程，是值在变化，还是索引在变化。

参考：

https://www.cnblogs.com/f-zhao/p/6380699.html

https://www.zhihu.com/question/31203609