LeetCode第二題：兩數相加

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode head = new ListNode(0);
        ListNode temp = head;
        int sum = 0;
        while(l1!=null || l2!=null || sum!=0){
            if(l1!=null){
                sum+=l1.val;
                l1 =l1.next;
            }
            if(l2!=null){
                sum+=l2.val;
                l2=l2.next;
            }
            int a = sum%10;
            ListNode next_ = new ListNode(a);
            temp.next = next_;
            temp = temp.next;
            sum = sum/10;
        }
        return head.next;
    }
}