129 lines
3.4 KiB
Rust
129 lines
3.4 KiB
Rust
#[derive(Debug)]
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enum BinaryTree<T> {
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Empty,
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NonEmpty(Box<TreeNode<T>>)
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}
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#[derive(Debug)]
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struct TreeNode<T> {
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element: T,
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left: BinaryTree<T>,
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right: BinaryTree<T>
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}
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impl<T> BinaryTree<T> {
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fn iter(&self) -> TreeIter<T> {
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let mut iter = TreeIter { unvisited: Vec::new() };
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iter.push_left_edge(self);
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iter
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}
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}
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impl<T: Ord> BinaryTree<T> {
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fn add(&mut self, value: T) {
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match *self {
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BinaryTree::Empty => *self = BinaryTree::NonEmpty(Box::new(TreeNode {
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element: value,
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left: BinaryTree::Empty,
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right: BinaryTree::Empty,
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})),
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BinaryTree::NonEmpty(ref mut node) => {
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if value <= node.element {
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node.left.add(value);
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} else {
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node.right.add(value);
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}
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}
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}
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}
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}
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impl<'a, T: 'a> IntoIterator for &'a BinaryTree<T> {
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type Item = &'a T;
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type IntoIter = TreeIter<'a, T>;
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fn into_iter(self) -> Self::IntoIter {
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self.iter()
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}
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}
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use self::BinaryTree::*;
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// The state of an in-order traversal of a `BinaryTree`
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struct TreeIter<'a, T: 'a> {
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// A stack of references to tree nodes. Since we use `Vec`'s
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// `push` and `pop` methods, the top of the stack is the end of the
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// vector.
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//
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// The node the iterator will visit next is at the top of the stack,
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// with those ancestors still unvisited below it. If the stack is empty,
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// the iteration is over
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unvisited: Vec<&'a TreeNode<T>>
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}
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impl<'a, T:'a> TreeIter<'a, T> {
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fn push_left_edge(&mut self, mut tree: &'a BinaryTree<T>) {
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while let NonEmpty(ref node) = *tree {
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self.unvisited.push(node);
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tree = &node.left;
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}
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}
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}
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impl<'a, T> Iterator for TreeIter<'a, T> {
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type Item = &'a T;
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fn next(&mut self) -> Option<&'a T> {
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// Find the node this iteration must produce,
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// or finish the iteration
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let node = match self.unvisited.pop() {
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None => return None,
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Some(n) => n,
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};
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// The next node after this one is the leftmost child of
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// this node's right child, so push the path from here down.
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self.push_left_edge(&node.right);
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// Produce a reference to this node's value.
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Some(&node.element)
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}
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}
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fn make_node<T>(left: BinaryTree<T>, element: T, right: BinaryTree<T>) -> BinaryTree<T> {
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NonEmpty(Box::new(TreeNode { left, element, right }))
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}
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fn main() {
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let mut tree = BinaryTree::Empty;
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tree.add("Mercury");
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tree.add("Venus");
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tree.add("Earth");
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tree.add("Mars");
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tree.add("Jupiter");
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tree.add("Saturn");
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tree.add("Uranus");
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tree.add("Neptune");
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tree.add("Pluto");
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println!("Tree: {:?}", tree);
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// Build a small tree
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let subtree_l = make_node(Empty, "mecha", Empty);
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let subtree_rl = make_node(Empty, "droid", Empty);
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let subtree_r = make_node(subtree_rl, "robot", Empty);
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let tree2 = make_node(subtree_l, "Jaeger", subtree_r);
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// Iterate over it.
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let mut v = Vec::new();
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for kind in &tree2 {
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v.push(*kind);
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}
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assert_eq!(v, ["mecha", "Jaeger", "droid", "robot"]);
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assert_eq!(tree2.iter()
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.map(|name| format!("mega-{}", name))
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.collect::<Vec<_>>(),
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vec!["mega-mecha", "mega-Jaeger", "mega-droid", "mega-robot"]
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);
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}
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