LeetCode 2. Add Two Numbers

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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

思路:
将长度较短的链表在末尾补零使得两个连表长度相等，再一个一个元素对其相加（考虑进位）
1.获取两个链表所对应的长度
2.在较短的链表末尾补零
3.对齐相加考虑进位

Solution:

public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode r = new ListNode(0);
        ListNode h = r;
        ListNode beforeend = r;

        while(l1 != null && l2!= null){
            r.val += l1.val + l2.val;

            r.next = new ListNode(r.val / 10);
            r.val %= 10;

            beforeend = r;
            r = r.next;
            l1 = l1.next;
            l2 = l2.next;
        }

        ListNode rest;
        if (l1 == null) rest = l2; else rest =l1;

        while(rest != null){
            r.val += rest.val;

            r.next = new ListNode(r.val / 10);
            r.val %= 10;

            beforeend = r;
            r = r.next;
            rest = rest.nest;
        }
        if(beforeend.next != null && beforeend.next.val == 0) beforeend.next=null;

        return h;
    }
}