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// @Title: 两数相加 (Add Two Numbers)
// @Author: 15816537946@163.com
// @Date: 2020-10-20 18:23:16
// @Runtime: 8 ms
// @Memory: 2 MB
// Definition for singly-linked list.
// #[derive(PartialEq, Eq, Clone, Debug)]
// pub struct ListNode {
//   pub val: i32,
//   pub next: Option<Box<ListNode>>
// }
//
// impl ListNode {
//   #[inline]
//   fn new(val: i32) -> Self {
//     ListNode {
//       next: None,
//       val
//     }
//   }
// }

impl Solution {
    pub fn add_two_numbers(
        l1: Option<Box<ListNode>>,
        l2: Option<Box<ListNode>>,
    ) -> Option<Box<ListNode>> {
        match (l1, l2) {
            (None, None) => None,
            (Some(n), None) | (None, Some(n)) => Some(n),
            (Some(n1), Some(n2)) => {
                let sum = n1.val + n2.val;
                if sum < 10 {
                    Some(Box::new(ListNode {
                        val: sum,
                        next: Solution::add_two_numbers(n1.next, n2.next),
                    }))
                } else {
                    let carry = Some(Box::new(ListNode::new(1)));
                    Some(Box::new(ListNode {
                        val: sum - 10,
                        next: Solution::add_two_numbers(
                            Solution::add_two_numbers(carry, n1.next),
                            n2.next,
                        ),
                    }))
                }
            }
        }
    }
}