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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Java

public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int carry = 0;
        ListNode rst = new ListNode(0);
        ListNode dummy = rst;
        ListNode first = l1, second = l2;

        while(first != null || second != null) {
            if(first != null) {
                carry += first.val;
                first = first.next;
            }
            if(second != null) {
                carry += second.val;
                second = second.next;
            }

            rst.next = new ListNode(carry % 10);
            rst = rst.next;
            carry /= 10;
        }

        if(carry != 0) {
            rst.next = new ListNode(carry);
        }
        return dummy.next;
    }
}