Method add_two_numbers

2. Add Two Numbers/src/main.rs:112–114

(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>)

    }

    pub fn add_two_numbers(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
        Self::add_two_numbers_recursive(l1.as_ref(), l2.as_ref(), 0)
    }
}