LeetCode两数之和

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if(l1==null){
            l1=new ListNode(0);
        }
        if(l2==null){
            l2=new ListNode(0);
        }
        if(l1.next==null&&l2.next==null){
            int sum =l1.val+l2.val;
            if(sum>9){
                ListNode node= new ListNode(sum%10);
                node.next=new ListNode(sum/10);
                return node;
            }else{
                return new ListNode(sum);
            }
        }else{
            int sum =l1.val+l2.val;
            if(sum>9){
                sum = sum-10;
                if(l1.next!=null){
                    l1.next.val++;
                }else if(l2.next!=null){
                    l2.next.val++;
                }
            }
             ListNode node=new ListNode(sum);
             node.next=addTwoNumbers(l1.next,l2.next);
             return node;
        }
    }
}