Leetcode 2. Add Two Numbers (java)

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode l3 = null;
        boolean add = false;
        while (l1 != null || l2 != null) {
            //位数相加
            int plus;
            if (l1 == null) {
                plus = l2.val;
            } else if (l2 == null) {
                plus = l1.val;
            } else {
                plus = l1.val + l2.val;
            }
            if (add) {
                plus++;
                add = false;
            }
            //生成节点
            ListNode temp;
            if (plus >= 10) {
                temp = new ListNode(plus % 10);
                add = true;
            } else {
                temp = new ListNode(plus);
            }
            //拼接节点
            ListNode l3Head = l3;
            if (l3 == null) {
                l3 = temp;
                if (add &&  (l1 == null || l1.next == null) && (l2 == null || l2.next == null)) {
                    l3.next = new ListNode(1);
                }
            } else {
                while (l3Head.next != null) {
                    l3Head = l3Head.next;
                }
                l3Head.next = temp;
                if (add &&  (l1 == null || l1.next == null) && (l2 == null || l2.next == null)) {
                    l3Head.next.next = new ListNode(1);
                }
            }
            //跳到下一位
            if (l1 == null) {
                l2 = l2.next;
            } else if (l2 == null) {
                l1 = l1.next;
            } else {
                l1 = l1.next;
                l2 = l2.next;
            }

        }
        return l3;
    }
}