leetcode 2. Add Two Numbers

題目：

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.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode start = new ListNode(0);
        ListNode cur = start;
        //標記是否有進位
        int count = 0;
        while (l1 != null && l2 != null) {
            int val = l1.val + l2.val + count;
            count = val / 10;
            val = val % 10;
            ListNode tmp = new ListNode(val);
            cur.next = tmp;
            cur = tmp;
            l1 = l1.next;
            l2 = l2.next;
        }
        while (l1 != null) {
            int val = l1.val + count;
            count = val / 10;
            val = val % 10;
            ListNode tmp = new ListNode(val);
            cur.next = tmp;
            cur = tmp;
            l1 = l1.next;
        }
        while (l2 != null) {
            int val = l2.val + count;
            count = val / 10;
            val = val % 10;
            ListNode tmp = new ListNode(val);
            cur.next = tmp;
            cur = tmp;
            l2 = l2.next;
        }
        if (count > 0) {
            ListNode tmp = new ListNode(count);
            cur.next = tmp;
        }
        return start.next;
    }
}