2 - Add Two Numbers

Problem

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.

Code

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode ret = new ListNode(0);
        ListNode t = ret;
        int p = 0;
        while (l1 != null && l2 != null) {
            int tmp = p + l1.val + l2.val;
            t.next = new ListNode(tmp % 10);
            p = tmp / 10;
            l1 = l1.next;
            l2 = l2.next;
            t = t.next;
        }
        while (l1 != null) {
            int tmp = p + l1.val;
            t.next = new ListNode(tmp % 10);
            p = tmp / 10;
            l1 = l1.next;
            t = t.next;
        }
        while (l2 != null) {
            int tmp = p + l2.val;
            t.next = new ListNode(tmp % 10);
            p = tmp / 10;
            l2 = l2.next;
            t = t.next;
        }
        if (p != 0) {
            t.next = new ListNode(p);
        }
        return ret.next == null ? ret : ret.next;
    }
}