AddTwoNumbers.java

package leetcode.list;

import leetcode.helpers.ListNode;

public class AddTwoNumbers {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode result = new ListNode(0);
        ListNode current = result;
        int carry = 0;

        while (l1 != null || l2 != null) {
            if (l1 != null && l2 != null) {
                current.next = new ListNode((l1.val + l2.val + carry) % 10);
                carry = (l1.val + l2.val + carry) / 10;
                l1 = l1.next;
                l2 = l2.next;
            } else if (l1 != null) {
                current.next = new ListNode((l1.val + carry) % 10);
                carry = (l1.val + carry) / 10;
                l1 = l1.next;
            } else {
                current.next = new ListNode((l2.val + carry) % 10);
                carry = (l2.val + carry) / 10;
                l2 = l2.next;
            }

            current = current.next;
        }

        if (carry != 0) {
            current.next = new ListNode(carry);
        }

        return result.next;
    }
}