mirror of https://github.com/smol-rs/vec-arena
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Stjepan Glavina
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4e6040f247
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89b77b634c
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@ -23,7 +23,8 @@ struct Splay<T> {
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root: usize,
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}
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impl<T> Splay<T> where T: Ord + Eq + Clone {
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impl<T> Splay<T> where T: Ord {
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/// Constructs a new, empty splay tree.
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fn new() -> Splay<T> {
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Splay {
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arena: VecArena::new(),
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@ -31,83 +32,120 @@ impl<T> Splay<T> where T: Ord + Eq + Clone {
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}
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}
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// #[inline(always)]
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fn rotate(&mut self, a: usize, b: usize) {
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let p = self.arena[a].parent;
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let dir = if self.arena[a].children[0] == b { 0 } else { 1 };
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let t = self.arena[b].children[dir ^ 1];
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self.arena[a].children[dir] = t;
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if t != !0 {
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self.arena[t].parent = a;
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/// Links nodes `p` and `c` as parent and child with the specified direction.
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#[inline(always)]
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fn link(&mut self, p: usize, c: usize, dir: usize) {
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self.arena[p].children[dir] = c;
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if c != !0 {
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self.arena[c].parent = p;
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}
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self.arena[b].children[dir ^ 1] = a;
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self.arena[a].parent = b;
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}
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if p == !0 {
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self.root = b;
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self.arena[b].parent = !0;
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/// Performs a rotation on node `c`, whose parent is node `p`.
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#[inline(always)]
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fn rotate(&mut self, p: usize, c: usize) {
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// Variables:
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// - `c` is the child node
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// - `p` is it's parent
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// - `g` is it's grandparent
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// Find the grandparent.
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let g = self.arena[p].parent;
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// The direction of p-c relationship.
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let dir = if self.arena[p].children[0] == c { 0 } else { 1 };
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// This is the child of `c` that needs to be reassigned to `p`.
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let t = self.arena[c].children[dir ^ 1];
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self.link(p, t, dir);
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self.link(c, p, dir ^ 1);
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if g == !0 {
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// There is no grandparent, so `c` becomes the root.
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self.root = c;
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self.arena[c].parent = !0;
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} else {
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let dir = if self.arena[p].children[0] == a { 0 } else { 1 };
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self.arena[p].children[dir] = b;
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self.arena[b].parent = p;
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// Link `g` and `c` together.
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let dir = if self.arena[g].children[0] == p { 0 } else { 1 };
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self.link(g, c, dir);
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}
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}
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fn splay(&mut self, a: usize) {
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/// Splays node
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fn splay(&mut self, c: usize) {
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loop {
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let b = self.arena[a].parent;
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if b == !0 {
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// Variables:
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// - `c` is the current node
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// - `p` is it's parent
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// - `g` is it's grandparent
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// Find the parent.
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let p = self.arena[c].parent;
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if p == !0 {
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// There is no parent. That means `c` is the root.
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break;
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}
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let c = self.arena[b].parent;
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if c == !0 {
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self.rotate(b, a);
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// Find the grandparent.
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let g = self.arena[p].parent;
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if g == !0 {
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// There is no grandparent. Just one rotation is left.
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// Zig step.
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self.rotate(p, c);
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break;
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}
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let is_l = self.arena[c].children[0] == b && self.arena[b].children[0] == a;
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let is_r = self.arena[c].children[1] == b && self.arena[b].children[1] == a;
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if is_l || is_r {
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self.rotate(c, b);
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self.rotate(b, a);
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if (self.arena[g].children[0] == p) == (self.arena[p].children[0] == c) {
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// Zig-zig step.
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self.rotate(g, p);
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self.rotate(p, c);
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} else {
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self.rotate(b, a);
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self.rotate(c, a);
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// Zig-zag step.
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self.rotate(p, c);
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self.rotate(g, c);
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}
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}
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}
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/// Inserts a new node with specified `value`.
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fn insert(&mut self, value: T) {
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let node = self.arena.insert(Node::new(value));
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// Variables:
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// - `n` is the new node
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// - `p` will be it's parent
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// - `c` is the present child of `p`
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let n = self.arena.insert(Node::new(value));
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if self.root == !0 {
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self.root = node;
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self.root = n;
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} else {
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let mut curr = self.root;
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let mut p = self.root;
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loop {
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let dir = if self.arena[node].value < self.arena[curr].value { 0 } else { 1 };
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let next = self.arena[curr].children[dir];
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// Decide whether to go left or right.
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let dir = if self.arena[n].value < self.arena[p].value { 0 } else { 1 };
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let c = self.arena[p].children[dir];
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if next == !0 {
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self.arena[curr].children[dir] = node;
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self.arena[node].parent = curr;
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self.splay(node);
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if c == !0 {
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self.link(p, n, dir);
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self.splay(n);
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break;
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} else {
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curr = next;
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}
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p = c;
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}
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}
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}
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/// Pretty-prints the subtree rooted at `node`, indented by `depth` spaces.
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fn print(&self, node: usize, depth: usize) where T: std::fmt::Display {
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if node != !0 {
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// Print the left subtree.
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self.print(self.arena[node].children[0], depth + 1);
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// Print the current node.
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println!("{:width$}{}", "", self.arena[node].value, width = depth * 3);
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// Print the right subtree.
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self.print(self.arena[node].children[1], depth + 1);
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}
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}
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@ -116,10 +154,13 @@ impl<T> Splay<T> where T: Ord + Eq + Clone {
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fn main() {
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let mut splay = Splay::new();
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// Insert a bunch of pseudorandom numbers.
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let mut num = 1u32;
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for _ in 0..1000000 {
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for _ in 0..30 {
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num = num.wrapping_mul(17).wrapping_add(255);
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splay.insert(num);
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}
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// splay.print(splay.root, 0);
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// Display the whole splay tree.
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splay.print(splay.root, 0);
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}
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