rust-reference

rust-reference.rs

// bad
pub fn remove_linked_list_elements(head: Option<Box<ListNode>>, val: i32) -> Option<Box<ListNode>> {
    let mut dummy = Some(Box::new(ListNode{val: 0, next: None}));
    let mut prev = dummy.as_mut();
    let mut curr = head;

    while let Some(mut node) = curr {
        curr = node.next.take();

        if node.val != val {
            // bad here
            prev.unwrap().next = Some(node);
            // but it's good
            // prev.as_mut().unwrap().next = Some(node);
            prev = prev.unwrap().next.as_mut();
        }
    }

    dummy?.next
}

// good
pub fn remove_linked_list_elements(head: Option<Box<ListNode>>, val: i32) -> Option<Box<ListNode>> {
    let mut dummy = Some(Box::new(ListNode{val: 0, next: None}));
    let mut prev = dummy.as_mut();
    let mut curr = head;

    while let Some(mut node) = curr {
        curr = node.next.take();

        if node.val != val {
            // good
            let pnode = prev.unwrap();
            pnode.next = Some(node);
            prev = pnode.next.as_mut();
        }
    }

    dummy?.next
}

// good
impl Solution {
    pub fn remove_elements(mut head: Option<Box<ListNode>>, val: i32) -> Option<Box<ListNode>> {
        let mut dummy = Some(Box::new(ListNode::new(0)));
        let mut next = dummy.as_mut();
        while let Some(mut inner) = head {
            head = inner.next.take();
            if inner.val != val {
                // good
                next.as_mut().unwrap().next = Some(inner);
                next = next.unwrap().next.as_mut();
            }
        }
        dummy.unwrap().next
    }
}

// good
pub fn remove_nth_from_end(head: Option<Box<ListNode>>, n: i32) -> Option<Box<ListNode>> {
    let mut length = 0;

    {
        let mut p = head.as_ref();
        while let Some(node) = p {
            length += 1;
            p = node.next.as_ref();
        }
    }

    let mut dummy = Some(Box::new(ListNode{val: 0, next: head}));
    let mut p = dummy.as_mut();

    for _ in 0..(length-n) {
        p = p.unwrap().next.as_mut();
    }

    // good
    let curr = p.unwrap();
    let del = curr.next.as_mut()?;
    curr.next = del.next.take();

    return dummy.unwrap().next;
}