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//! Necessary types for storing and interacting with trees. #![deny(missing_docs)] /// An error enum returned when attempting to build a [Sapling][Sapling]. #[derive(Debug, PartialEq)] pub enum Error { /// The sapling is incomplete and not ready to be built. /// /// It is either empty or there are still unfinished nodes. Incomplete, /// The sapling contains more than one root node. /// /// When creating nodes on a sapling it is possible to `pop()` the root node /// and `push(_)` a second root. Trees however must have a unique root. MultipleRoots, } /// An internal struct that stores the payload and relationships of a node on a /// tree. /// /// Every node on the tree is represented by a vertex. The `len` field stores /// the number of descendants the node has; this is the number of nodes in the /// subtree below the node. A leaf node has length `0`. #[derive(Debug, Clone, Copy)] struct Vertex<T> { len: usize, data: T, } /// A builder to construct [Tree][Tree]s. /// /// Saplings are the only way of creating trees. New saplings are initialized /// empty, containing no nodes. Nodes are then added to the sapling until the /// tree is complete. The sapling can then be turned into a tree. /// /// Nodes are added to saplings using `.push(_)`. Adding a new node also selects /// it, meaning later calls of `.push(_)` will attach the new node as a child to /// this one. To close a node once all its child nodes have been added, call /// `.pop()`. When adding a node that will not have any child nodes, use /// `.push_leaf(_)`; this acts the same as `.push(_); .pop();`. /// /// When the sapling is complete, turn it into a tree using `.build()`. This /// function returns a `Result<_, _>` to indicate if the sapling was built /// successfully. To check if a sapling is ready to be built call `.is_ready()`. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// assert!(sap.is_empty()); /// /// sap.push(1); // Add a new node to the tree carrying the payload `1`. /// sap.push_leaf(11); // Add a child node to node `1`. This node will have no children. /// /// sap.push(12); // Add another child node to `1`. Select this node. /// sap.push_leaf(121); // Add leaf nodes to node `12`. /// sap.push_leaf(122); /// /// sap.pop(); // Close node `12`. /// sap.pop(); // Close node `1`. /// /// assert!(sap.is_ready()); /// let _tree = sap.build().unwrap(); /// ``` #[derive(Debug)] pub struct Sapling<T> { path: Vec<usize>, verts: Vec<Vertex<T>>, } impl<T> Sapling<T> { /// Creates a new empty sapling. /// /// An empty sapling is not yet ready to be built. Add at least one node /// before building it into a tree. /// /// ```rust /// let sap = read_tree::Sapling::<usize>::new(); /// assert!(sap.is_empty()); /// assert!(sap.build().is_err()); /// ``` pub fn new() -> Self { Sapling { path: Vec::new(), verts: Vec::new(), } } /// Creates a new empty sapling with enough capacity to store `len` many /// nodes. /// /// The sapling is allowed to receive more than `len` nodes; this may /// however cause additional allocations. /// /// The optional parameter `depth` should predict the maximum depth of the /// tree. If the depth is unknown use `None`. The depth should include the /// root node, can however exclude leaf nodes, if the leaf nodes will be /// added using `.push_leaf(_)`. Essentially every call to `push(_)` /// increases the depth, and every call to `pop()` decreases it. pub fn with_capacity(len: usize, depth: Option<usize>) -> Self { Sapling { path: Vec::with_capacity(depth.unwrap_or(0)), verts: Vec::with_capacity(len), } } /// Adds a new node with the payload `data` to the sapling. /// /// Until `.pop()` is called new nodes will be attached to this new node. To /// avoid changing the selected node use `.push_leaf(_)` instead. /// /// Note that nodes have to be added to the sapling in the correct oder. /// Once a node has been closed using `.pop()` its subtree is finalized and /// can no longer be changed. pub fn push(&mut self, data: T) { self.path.push(self.verts.len()); self.verts.push(Vertex { len: 0, data }); } /// Adds a new leaf node with the payload `data` to the sapling. pub fn push_leaf(&mut self, data: T) { self.verts.push(Vertex { len: 0, data }); } /// Adds another tree to the selected node in the sapling. Does not change /// the selected node, similar to `.push_leaf(_)`. /// /// Empties `tree` in the process and returns it as an empty sapling. pub fn push_tree(&mut self, tree: Tree<T>) -> Sapling<T> { let mut sap = tree.into_sapling(); self.verts.append(&mut sap.verts); sap.clear(); sap } /// Returns a reference to the payload of the selected node. Returns `None` /// if no node is currently selected; this happens when the sapling is empty /// or after a root node was closed. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(0); /// sap.push(1); /// /// assert_eq!(sap.pop(), Some(&1)); /// /// assert_eq!(sap.peek(), Some(&0)); /// assert_eq!(sap.pop(), Some(&0)); /// /// sap.build().unwrap(); /// ``` pub fn peek(&self) -> Option<&T> { let i = *self.path.last()?; Some(&self.verts[i].data) } /// Closes the current node. /// /// The subtree under the current node is complete and will be closed. From /// now on new nodes will be attached to the parent of the closed node. /// /// Returns a reference to the payload of the closed node. Returns `None` if /// no node is currently selected; this happens when the sapling is empty or /// after a root node was closed. /// /// # Examples /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(0); /// assert_eq!(sap.pop(), Some(&0)); /// sap.build().unwrap(); /// ``` /// /// ```rust /// let mut sap = read_tree::Sapling::<usize>::new(); /// assert_eq!(sap.pop(), None); /// ``` /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push_leaf(0); /// assert_eq!(sap.pop(), None); /// ``` pub fn pop(&mut self) -> Option<&T> { let i = self.path.pop()?; self.verts[i].len = self.verts.len() - i - 1; Some(&self.verts[i].data) } /// Closes all open nodes. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(0); /// sap.push(1); /// sap.push(2); /// sap.pop_all(); /// /// let _tree = sap.build().unwrap(); /// ``` pub fn pop_all(&mut self) { while let Some(i) = self.path.pop() { self.verts[i].len = self.verts.len() - i - 1; } } /// Closes the current node and makes it a leaf node. /// /// Any nodes that were attached to the current node will be attached to its /// parent node instead. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(0); /// sap.push(1); /// sap.push_leaf(2); /// /// // make `1` a leaf node; changing `2` to be a child of `0` /// sap.pop_as_leaf(); /// sap.pop(); /// let tree = sap.build().unwrap(); /// let mut iter = tree.root().children(); /// /// assert_eq!(iter.next().unwrap().data(), &1); /// assert_eq!(iter.next().unwrap().data(), &2); /// ``` pub fn pop_as_leaf(&mut self) -> Option<&T> { let i = self.path.pop()?; Some(&self.verts[i].data) } /// Closes all open nodes and makes them all leaf nodes. /// /// If there are open nodes in the sapling, this will cause multiple root /// nodes. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(0); /// sap.push(1); /// sap.pop_as_leaf_all(); /// assert_eq!(sap.build().unwrap_err().1, read_tree::Error::MultipleRoots); /// ``` pub fn pop_as_leaf_all(&mut self) { self.path.clear(); } /// Removes all nodes from the sapling, making it empty. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push_leaf(0); /// assert_eq!(sap.is_empty(), false); /// /// sap.clear(); /// assert_eq!(sap.is_empty(), true); /// ``` pub fn clear(&mut self) { self.path.clear(); self.verts.clear(); } /// Returns `true` if the sapling contains no nodes. Use `push(_)` to add /// nodes. pub fn is_empty(&self) -> bool { self.verts.is_empty() } /// Return `true` if the sapling is ready to be built. /// /// Verifies that the sapling is not empty and has no open nodes. It does /// not verify the number of root nodes of the sapling. Building into a /// [Tree][Tree] may still fail because trees do not allow multiple root /// nodes. pub fn is_ready(&self) -> bool { self.path.is_empty() && !self.verts.is_empty() } /// Builds the sapling into a tree. /// /// Consumes the sapling in the process. Fails when the sapling is /// incomplete or has multiple roots. When failing to build the sapling, the /// sapling is returned unmodified with the error. pub fn build(self) -> Result<Tree<T>, (Sapling<T>, Error)> { if !self.is_ready() { return Err((self, Error::Incomplete)); } if self.verts[0].len < self.verts.len() - 1 { return Err((self, Error::MultipleRoots)); } Ok(Tree { path: self.path, verts: self.verts, }) } } impl<T: Clone> Sapling<T> { /// Clones the contents of a node and attaches the cloned subtree to the /// sapling. /// /// This is a relatively expensive step. The tree that `node` references is /// unaffected. pub fn push_node(&mut self, node: Node<T>) { self.verts.extend_from_slice(node.verts); } } /// A read-only tree data structure. /// /// Trees are created by [Sapling][Sapling]s. Most interactions with trees /// happen on slices of them called [Node][Node]s. Get a node representing the /// entire tree using `.root()`. #[derive(Debug)] pub struct Tree<T> { path: Vec<usize>, verts: Vec<Vertex<T>>, } impl<T> Tree<T> { /// Returns the unique root node of the tree representing the entire tree. /// /// You can think of this as taking the complete slice of the tree similar /// to `&vec[..]` for a [Vec][std::vec::Vec]. pub fn root(&self) -> Node<'_, T> { Node { depth: 0, verts: &self.verts[..], } } /// Returns the number of nodes in the tree. pub fn len(&self) -> usize { self.verts.len() } /// Turns the tree back into a sapling. No nodes are removed from the /// tree; building the returned sapling will result in an equivalent tree. pub fn into_sapling(self) -> Sapling<T> { Sapling { path: self.path, verts: self.verts, } } } /// A slice of a [Tree][Tree]. /// /// A node is essentially the same as a tree, only that it does not own its /// data. You can navigate a node using iterators. #[derive(Debug)] pub struct Node<'a, T> { depth: usize, verts: &'a [Vertex<T>], } impl<'a, T> Node<'a, T> { /// Returns a reference to the payload of the node. pub fn data(&self) -> &T { &self.verts[0].data } /// Returns the depth of the node within the tree. The root node returns /// depth `0`. pub fn depth(&self) -> usize { self.depth } /// Returns the number of nodes within the subtree of this node. /// /// The count includes the node itself; a leaf node returns length `1`. pub fn len(&self) -> usize { self.verts.len() } /// Returns `true` if the node has no child nodes. pub fn is_leaf(&self) -> bool { self.verts.len() == 1 } /// Returns a depth first iterator of nodes. It iterates all nodes in the /// subtree of the node, including the node itself. See /// [Descendants][Descendants] for more information. pub fn iter(&self) -> Descendants<'a, T> { Descendants { depth: self.depth, verts: self.verts, pos: 0, } } /// Returns an iterator over the child nodes of the node. See /// [Children][Children] for more information. pub fn children(&self) -> Children<'a, T> { Children { child_depth: self.depth + 1, verts: &self.verts[1..], } } } impl<'a, T: Clone> Node<'a, T> { /// Clones the subtree of the node into a new tree. /// /// This step may be expensive and should be avoided if possible. pub fn into_tree(self) -> Tree<T> { let mut verts = Vec::new(); verts.extend_from_slice(self.verts); Tree { path: Vec::new(), verts, } } } /// A depth first iterator of nodes. It iterates all nodes in the subtree of the /// node, including the node itself. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(1); /// sap.push_leaf(11); /// sap.push(12); /// sap.push_leaf(121); /// sap.pop(); /// sap.pop(); /// let tree = sap.build().unwrap(); /// let mut iter = tree.root().iter(); /// /// assert_eq!(iter.next().unwrap().data(), &1); /// assert_eq!(iter.next().unwrap().data(), &11); /// assert_eq!(iter.next().unwrap().data(), &12); /// assert_eq!(iter.next().unwrap().data(), &121); /// assert!(iter.next().is_none()); /// ``` #[derive(Debug)] pub struct Descendants<'a, T> { depth: usize, verts: &'a [Vertex<T>], pos: usize, } impl<'a, T> Iterator for Descendants<'a, T> { type Item = Node<'a, T>; fn next(&mut self) -> Option<Self::Item> { let verts = &self.verts[self.pos..self.pos + self.verts.get(self.pos)?.len + 1]; let mut depth = self.depth; let mut i = 0; while i < self.pos { let len = self.verts[i].len; if i + len < self.pos { i += len + 1; } else { depth += 1; i += 1; } } self.pos += 1; Some(Node { depth, verts }) } fn size_hint(&self) -> (usize, Option<usize>) { (self.verts.len(), Some(self.verts.len())) } fn count(self) -> usize { self.verts.len() } } /// An iterator of child nodes. /// /// # Example /// /// ```rust /// let mut sap = read_tree::Sapling::new(); /// sap.push(1); /// sap.push_leaf(11); /// sap.push(12); /// sap.push_leaf(121); /// sap.pop(); /// sap.pop(); /// let tree = sap.build().unwrap(); /// let mut iter = tree.root().children(); /// /// assert_eq!(iter.next().unwrap().data(), &11); /// assert_eq!(iter.next().unwrap().data(), &12); /// assert!(iter.next().is_none()); /// ``` #[derive(Debug)] pub struct Children<'a, T> { child_depth: usize, verts: &'a [Vertex<T>], } impl<'a, T> Iterator for Children<'a, T> { type Item = Node<'a, T>; fn next(&mut self) -> Option<Self::Item> { let (verts, remainder) = &self.verts.split_at(self.verts.get(0)?.len + 1); self.verts = remainder; Some(Node { depth: self.child_depth, verts, }) } fn size_hint(&self) -> (usize, Option<usize>) { if self.verts.is_empty() { (0, Some(0)) } else { (1, Some(self.verts.len())) } } }