## 369. Plus One Linked List

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

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

Example 1:

```Input: head = [1,2,3]
Output: [1,2,4]
```

Example 2:

```Input: head = 
Output: 
```

Constraints:

• The number of nodes in the linked list is in the range `[1, 100]`.
• `0 <= Node.val <= 9`
• The number represented by the linked list does not contain leading zeros except for the zero itself.

## Rust Solution

``````struct Solution;
use rustgym_util::*;

trait Plus {
}

fn plus(self) -> (ListLink, i32) {
if let Some(mut node) = self {
let val = node.val;
let next = node.next.take();
if next.is_some() {
let (tail, carry) = next.plus();
node.next = tail;
node.val = (val + carry) % 10;
let carry = (val + carry) / 10;
(Some(node), carry)
} else {
node.val = (val + 1) % 10;
let carry = (val + 1) / 10;
(Some(node), carry)
}
} else {
(None, 0)
}
}
}

impl Solution {
if carry == 1 {
} else {
tail
}
}
}

#[test]
fn test() {
let head = list!(1, 2, 3);
let res = list!(1, 2, 4);