[LeetCode] Add Two Numbers

public class AddTwoNumbers {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode answer = new ListNode();
        ListNode node = answer;
 
        int carry = 0;
 
        while (l1 != null || l2 != null){
            int sum = carry;
            if(l1 != null){
                sum += l1.val;
                l1 = l1.next;
            }
            if(l2 != null){
                sum += l2.val;
                l2 = l2.next;
            }
 
            carry = sum/10;
            sum %= 10;
 
            ListNode temp = new ListNode(sum);
            node.next = temp;
            node = node.next;
        }
        if(carry > 0){
            ListNode temp = new ListNode(carry);
            node.next = temp;
        }
 
        return answer.next;
    }
}
 
 
public class ListNode {
    public int val;
    public ListNode next;
 
    ListNode() {
    }
 
    ListNode(int val) {
        this.val = val;
    }
 
    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }
}