### 题目

Given a non-negative integer represented as non-empty a singly linked list of digits, plus one to the integer.

You may assume the integer do not contain any leading zero, except the number 0 itself.

The digits are stored such that the most significant digit is at the head of the list.

Example:

Input:
1->2->3

Output:
1->2->4


### 利用递归模拟“双向链表”

#### 代码

class Solution {
if (carry == 1) {
}
}