2. 两数相加 - 力扣(Leetcode)
class Solution {public ListNode addTwoNumbers(ListNode l1, ListNode l2) {if (l1==null&&l2==null){return null;}if (l1==null){l1=new ListNode(0);}if (l2==null){l2=new ListNode(0);}int sum=l1.val+l2.val;if (sum>9){if (l1.next==null){l1.next=new ListNode(0);}l1.next.val++;return new ListNode(sum%10,addTwoNumbers(l1.next,l2.next));}return new ListNode(sum,addTwoNumbers(l1.next,l2.next));}
}