Algorithm:

public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode node = new ListNode(null);
        ListNode p = node;
        int carry = 0;
        while (l1 != null || l2 != null) {
            int sum = carry;
            if (l1 != null && l1.val != null) {
                sum += l1.val;
                l1 = l1.next;
            }
            if (l2 != null && l2.val != null) {
                sum += l2.val;
                l2 = l2.next;
            }
            carry = sum / 10;
            p.next = new ListNode(sum % 10);
            p = p.next;
        }
        if (carry > 0) {
            p.next = new ListNode(1);
        }
        return node.next;
    }

Tip:
Redis过期机制 https://www.jianshu.com/p/0e13fcdc8fa1
Share：
Java内存模型 https://time.geekbang.org/column/article/13484