[LeetCode] 2. Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        
        ListNode r = new ListNode(0); // dummy node
        ListNode t = r;
        int carrying = 0;
        
        while (l1 != null || l2 != null || carrying != 0) {
            t.next = new ListNode(carrying);
            if (l1 != null) {
                t.next.val += l1.val;
                l1 = l1.next;
            }
            if (l2 != null) {
                t.next.val += l2.val;
                l2 = l2.next;
            }
            if (t.next.val >= 10) {
                t.next.val -= 10;
                carrying = 1;
            } else {
                carrying = 0;
            }
            t = t.next;
        }
        
        return r.next;
    }
}