~nerosnm/advela

ref: f938891641ff403ae7816006d3fcfd993639bf26 advela/src/node.rs -rw-r--r-- 11.5 KiB
f9388916Søren Mortensen Implement height and balance calculation 11 months ago
                                                                                
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//! A node in an [AvlTree][crate::tree::AvlTree].

use std::cmp::Ordering;

#[derive(Debug)]
pub struct AvlNode<T>
where
    T: Ord,
{
    /// The value contained in the node.
    val: T,
    /// The left child of this node, if there is one.
    left: Option<Box<AvlNode<T>>>,
    /// The right child of this node, if there is one.
    right: Option<Box<AvlNode<T>>>,
    /// The balance factor of this node, updated after each insertion and
    /// balance.
    ///
    /// Since the tree is balanced after each insertion, this should never be
    /// outside the range `[-2, 2]`.
    balance: i8,
    /// The height of this node, defined as the length of the path to its lowest
    /// child.
    height: u32,
}

impl<T> AvlNode<T>
where
    T: Ord,
{
    /// Create a new node containing the given value, with no children.
    pub fn new(val: T) -> Self {
        Self {
            val,
            left: None,
            right: None,
            balance: 0,
            height: 0,
        }
    }

    /// Set the left child of this node to the given node.
    pub fn set_left<V>(&mut self, val: V)
    where
        V: Into<AvlNode<T>>,
    {
        self.left = Some(val.into().into());
        self.update();
    }

    /// Set the right child of this node to the given node.
    pub fn set_right<V>(&mut self, val: V)
    where
        V: Into<AvlNode<T>>,
    {
        self.right = Some(val.into().into());
        self.update();
    }

    /// Get the balance factor of this node.
    pub fn balance(&self) -> i8 {
        self.balance
    }

    /// Get the height of this node.
    pub fn height(&self) -> u32 {
        self.height
    }

    /// Update the height and balance factor of this node to reflect that a
    /// change in the heights of the child nodes may have occurred.
    pub fn update(&mut self) {
        let left = self.left.as_ref().map(|l| l.height() as i64).unwrap_or(-1);
        let right = self.right.as_ref().map(|r| r.height() as i64).unwrap_or(-1);

        self.height = (left.max(right) + 1) as u32;
        self.balance = (right - left) as i8;
    }

    /// Insert a value into the subtree that has this node as its root.
    ///
    /// If the value already exists in the subtree, nothing will be changed.
    pub fn insert<V>(&mut self, val: V)
    where
        V: Into<T>,
    {
        let val = val.into();

        match val.cmp(&self.val) {
            Ordering::Equal => {
                // We can't insert duplicate values, so don't do anything.
            }
            Ordering::Less => {
                if let Some(ref mut left) = self.left {
                    left.insert(val);
                } else {
                    self.left = Some(val.into());
                }

                self.update();
            }
            Ordering::Greater => {
                if let Some(ref mut right) = self.right {
                    right.insert(val);
                } else {
                    self.right = Some(val.into());
                }

                self.update();
            }
        }
    }

    /// Return whether the given value is present anywhere in the subtree with
    /// this node as its root.
    pub fn contains(&self, val: &T) -> bool {
        match val.cmp(&self.val) {
            Ordering::Equal => true,
            Ordering::Less => self
                .left
                .as_ref()
                .map(|left| left.contains(val))
                .unwrap_or(false),
            Ordering::Greater => self
                .right
                .as_ref()
                .map(|right| right.contains(val))
                .unwrap_or(false),
        }
    }
}

#[cfg(feature = "print")]
impl<T> AvlNode<T>
where
    T: Ord,
    T: std::fmt::Display,
{
    /// Print the subtree that has this node as its root node.
    pub fn print(&self) -> String {
        self.print_at_level(0)
    }

    /// Print the subtree that has this node as its root node, adding `2 *
    /// level` spaces to the beginning of each line, to represent depth in a
    /// containing tree.
    fn print_at_level(&self, level: usize) -> String {
        let mut buf = String::new();

        (0..level).for_each(|_| buf.push_str("  "));
        buf.push_str(&format!("{}", self.val));
        buf.push('\n');

        if let Some(ref left) = self.left {
            buf.push_str(&left.print_at_level(level + 1));
        }

        if let Some(ref right) = self.right {
            buf.push_str(&right.print_at_level(level + 1));
        }

        buf
    }
}

impl<T> From<T> for AvlNode<T>
where
    T: Ord,
{
    fn from(val: T) -> Self {
        Self::new(val)
    }
}

impl<T> From<T> for Box<AvlNode<T>>
where
    T: Ord,
{
    fn from(val: T) -> Self {
        Box::new(val.into())
    }
}

#[cfg(test)]
pub struct AvlNodeBuilder<T>
where
    T: Ord,
{
    val: T,
    left: Option<T>,
    right: Option<T>,
}

#[cfg(test)]
impl<T> AvlNodeBuilder<T>
where
    T: Ord,
{
    pub fn new(val: T) -> Self {
        Self {
            val,
            left: None,
            right: None,
        }
    }

    pub fn left(mut self, val: T) -> Self {
        self.left = Some(val);
        self
    }

    pub fn right(mut self, val: T) -> Self {
        self.right = Some(val);
        self
    }

    pub fn build(self) -> AvlNode<T> {
        let mut node = AvlNode::<T>::new(self.val);

        if let Some(left) = self.left {
            node.set_left(left);
        }

        if let Some(right) = self.right {
            node.set_right(right);
        }

        node
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Test that the height of a node is correctly updated when children are
    /// inserted below it, starting by inserting on the left side (a
    /// lesser-valued child).
    #[test]
    fn update_height_insert_lesser_first() {
        let mut root = AvlNode::new(2);
        assert_eq!(
            root.height(),
            0,
            "the height of a node with no children should be 0"
        );

        //   2
        //  /
        // 1
        root.insert(1);
        assert_eq!(
            root.height(),
            1,
            "the height of a node should be updated when a lesser leaf is \
            inserted"
        );

        //   2
        //  /\
        // 1  3
        root.insert(3);
        assert_eq!(
            root.height(),
            1,
            "the height of a node should not change when a second child is \
            inserted with equal height to the first"
        );

        //   2
        //  /\
        // 1  3
        //    \
        //     4
        root.insert(4);
        assert_eq!(
            root.height(),
            2,
            "the height of a node should be updated when one child's height \
            becomes bigger than the other"
        );
    }

    /// Test that the height of a node is correctly updated when children are
    /// inserted below it, starting by inserting on the right side (a
    /// greater-valued child).
    #[test]
    fn update_height_insert_greater_first() {
        let mut root = AvlNode::new(2);
        assert_eq!(
            root.height(),
            0,
            "the height of a node with no children should be 0"
        );

        // 2
        // \
        //  3
        root.insert(3);
        assert_eq!(
            root.height(),
            1,
            "the height of a node should be updated when a greater leaf is \
            inserted"
        );

        //   2
        //  /\
        // 1  3
        root.insert(1);
        assert_eq!(
            root.height(),
            1,
            "the height of a node should not change when a second child is \
            inserted with equal height to the first"
        );

        //     2
        //    /\
        //   1  3
        //  /
        // 0
        root.insert(0);
        assert_eq!(
            root.height(),
            2,
            "the height of a node should be updated when one child's height \
            becomes bigger than the other"
        );
    }

    /// Test that the height of a node is correctly updated when children are
    /// directly set below it.
    #[test]
    fn update_height_set() {
        let mut root = AvlNode::new(2);
        assert_eq!(
            root.height(),
            0,
            "the height of a node with no children should be 0"
        );

        root.set_left(1);
        assert_eq!(root.height(), 1, "the height of the node should be 1");

        let height_1 = AvlNodeBuilder::new(3).right(4).build();
        root.set_right(height_1);

        assert_eq!(root.height(), 2, "the height of the node should be 2");
    }

    /// Test that the balance of a node is correctly updated when children are
    /// inserted below it, starting by inserting on the left side (a
    /// lesser-valued child).
    #[test]
    fn update_balance_insert_lesser_first() {
        let mut root = AvlNode::new(2);
        assert_eq!(
            root.balance(),
            0,
            "the balance of a node with no children should be 0"
        );

        //   2
        //  /
        // 1
        root.insert(1);
        assert_eq!(
            root.balance(),
            -1,
            "the balance of a node should be updated when a lesser leaf is \
            inserted"
        );

        //   2
        //  /\
        // 1  3
        root.insert(3);
        assert_eq!(
            root.balance(),
            0,
            "the balance of a node should be updated when a second child is \
            inserted with equal height to the first"
        );

        //   2
        //  /\
        // 1  3
        //    \
        //     4
        root.insert(4);
        assert_eq!(
            root.balance(),
            1,
            "the balance of a node should be updated when one child's height \
            becomes bigger than the other"
        );
    }

    /// Test that the balance of a node is correctly updated when children are
    /// inserted below it, starting by inserting on the right side (a
    /// greater-valued child).
    #[test]
    fn update_balance_insert_greater_first() {
        let mut root = AvlNode::new(2);
        assert_eq!(
            root.balance(),
            0,
            "the balance of a node with no children should be 0"
        );

        // 2
        // \
        //  3
        root.insert(3);
        assert_eq!(
            root.balance(),
            1,
            "the balance of a node should be updated when a greater leaf is \
            inserted"
        );

        //   2
        //  /\
        // 1  3
        root.insert(1);
        assert_eq!(
            root.balance(),
            0,
            "the balance of a node should be updated when a second child is \
            inserted with equal height to the first"
        );

        //     2
        //    /\
        //   1  3
        //  /
        // 0
        root.insert(0);
        assert_eq!(
            root.balance(),
            -1,
            "the balance of a node should be updated when one child's height \
            becomes bigger than the other"
        );
    }

    /// Test that the balance of a node is correctly updated when children are
    /// directly set below it.
    #[test]
    fn update_balance_set() {
        let mut root = AvlNode::new(2);
        assert_eq!(
            root.balance(),
            0,
            "the balance of a node with no children should be 0"
        );

        root.set_left(1);
        assert_eq!(root.balance(), -1, "the balance of the node should be -1");

        let balance_1 = AvlNodeBuilder::new(3).right(4).build();
        root.set_right(balance_1);

        assert_eq!(root.balance(), 1, "the balance of the node should be 1");
    }
}