【力扣题目】两数相加（链表）

https://leetcode.cn/problems/add-two-numbers/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
       
        ListNode root = new ListNode();           // 返回值
        ListNode cursor = root;                     // 游标
        int carry = 0;          // 进位
        
        while(l1 != null || l2 != null || carry != 0){
           
            // 循环计算节点位(节点1+节点2—— 进位)
            int sumVal = (l1 != null ? l1.val : 0 ) + (l2 != null ? l2.val : 0) + carry;
            carry = sumVal /10; 
            // 添加新结点，并下移两个结点
            ListNode sumNode = new ListNode(sumVal%10);
            cursor.next =  sumNode;
            cursor = cursor.next;
            
            
          l1 = (l1 != null ? l1.next:l1);
          l2 = (l2 != null? l2.next : l2);
        }
        return root.next;
    }
}