leetcode 力扣 2 两数相加

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode pre = new ListNode(0);
        ListNode cur = pre;
        int carry = 0;
        int sum = 0;
        while(l1 != null || l2 != null){
            int x = l1 == null ? 0 : l1.val;
            int y = l2 == null ? 0 : l2.val;
            sum = x + y + carry;
            carry = sum / 10;
            sum = sum % 10;

            cur.next = new ListNode(sum);
            cur = cur.next;
            
            if(l1 != null){
                l1 = l1.next;
            }
            if(l2 != null){
                l2 = l2.next;
            }
        }

        if(carry == 1){
            cur.next = new ListNode(1);
        }

        return pre.next;
    }

两个链表从左往右逐个相加，短的链表空结点补0即可，使用尾插法往新的链表插入结果，如果最后一位需要进1，新增一个结点为1即可