LeetCode No.2

public class ListNode {
    int val;
    ListNode next;

    public ListNode(int val) {
        this.val = val;
    }
}
class Solution{
    public ListNode addTwoNumbers(ListNode l1,ListNode l2){
        ListNode pre=new ListNode(0);
        ListNode temp=pre;
        int carry=0;
        while (l1!=null||l2!=null){//当l1,l2都等于null时才跳出
            int x=l1==null?0:l1.val;
            int y=l2==null?0:l2.val;
            int sum=x+y+carry;

            carry=sum/10;
            sum=sum%10;
            temp.next=new ListNode(sum);

            temp=temp.next;
            if (l1!=null){
                l1=l1.next;
            }
            if (l2!=null){
                l2=l2.next;
            }
        }
        if (carry==1){
            temp.next=new ListNode(carry);
        }
        return pre.next;//输出时个位在前
    }
}