Reverse singly linkedlist

reverse_singly_linkedlist.rs

#[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 }
    }
}

fn reverse_until<'a>(
    begin: Option<Box<ListNode>>,
    end: Option<&'a Box<ListNode>>,
) -> Option<Box<ListNode>> {
    let mut prev = None;
    let mut cur = begin;

    while cur.as_ref() != end {
        let mut cur_unwrap = cur.unwrap();
        let next = cur_unwrap.next.take();
        cur_unwrap.next = prev.take();

        prev = Some(cur_unwrap);
        cur = next;
    }

    return prev;
}

fn reverse(begin: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
    reverse_until(begin, None)
}