AddTwoNumbers.java

public class AddTwoNumbers {
    public static class ListNode {
        int val;
        ListNode next;
        ListNode() {}
        ListNode(int val) { this.val = val; }
        ListNode(int val, ListNode next) { this.val = val; this.next = next; }
    }

    public ListNode addTwoNumbers(ListNode l1, ListNode l2){
        ListNode dummy = new ListNode(0);
        ListNode current = dummy;
        int carry = 0;
        while (l1 != null || l2 != null) {
            int x = (l1 != null) ? l1.val : 0;
            int y = (l2 != null) ? l2.val : 0;
            int sum = x + y + carry;

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

            if (l1 != null){
                l1 = l1.next;
            }else{
                l1 = null;
            }

            if (l2 != null){
                l2 = l2.next;
            }else{
                l2 = null;
            }
        }
        if (carry > 0) {
            current.next = new ListNode(carry);
        }
        return dummy.next;
    }

    public static void main(String[] args) {
        AddTwoNumbers solution = new AddTwoNumbers();
        ListNode l1 = new ListNode(2, new ListNode(4, new ListNode(3)));
        ListNode l2 = new ListNode(5, new ListNode(6, new ListNode(4)));
        ListNode result = solution.addTwoNumbers(l1, l2);
        while (result != null) {
            System.out.println(result.val);
            result = result.next;
        }
    }
}