Leetcode. Add two numbers task

Task

You are given two non-empty linked lists representing two non-negative integers. 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. You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        return addTwoNumbers(l1,l2,0);
    }

    private ListNode addTwoNumbers(ListNode l1, ListNode l2, int delta) {
        if ((l1 == null) && (l2 == null) && (delta == 0)) return null;

        int val1 = (l1 == null) ? 0 : l1.val;
        int val2 = (l2 == null) ? 0 : l2.val;

        int val = val1 + val2 + delta;

        delta = 0;
        if (val > 9) {
            val = val - 10;
            delta = 1;
        }
        ListNode l3 = new ListNode(val);

        ListNode nl1 = (l1 == null) ? null : l1.next;
        ListNode nl2 = (l2 == null) ? null : l2.next;
        l3.next = addTwoNumbers(nl1,nl2, delta);
        return l3;
    }

}

Results

• Runtime: 1 ms, faster than 100.00% of Java online submissions for Add Two Numbers.
• Memory Usage: 39.2 MB, less than 100.00% of Java online submissions for Add Two Numbers.